General Science Review: Chemistry

Atoms
Matter refers to substances that have mass and occupy space (or volume). The traditional definition of matter describes it as having three states: solid, liquid, and gas. These different states are caused by differences in the distances and angles between molecules or atoms, which result in differences in the energy that binds them. Solid structures are rigid or nearly rigid and have strong bonds. Molecules or atoms of liquids move around and have weak bonds, although they are not weak enough to readily break. 

Molecules or atoms of gases move almost independently of each other, are typically far apart, and do not form bonds. The current definition of matter describes it as having four states. The fourth is plasma, which is an ionized gas that has some electrons that are described as free because they are not bound to an atom or molecule.

All matter consists of atoms.
Atoms consist of a nucleus and electrons. The nucleus consists of protons and neutrons. The properties of these are measurable; they have mass and an electrical charge. The nucleus is positively charged due to the presence of protons. Electrons are negatively charged and orbit the nucleus. The nucleus has considerably more mass than the surrounding electrons. Atoms can bond together to make molecules. Atoms that have an equal number of protons and electrons are electrically neutral. If the number of protons and electrons in an atom is not equal, the atom has a positive or negative charge and is an ion.

An element is matter with one particular type of atom. It can be identified by its atomic number, or the number of protons in its nucleus. There are approximately 117 elements currently known, 94 of which occur naturally on Earth.  Elements from the periodic table include hydrogen, carbon, iron, helium, mercury, and oxygen. Atoms combine to form molecules. For example, two atoms of hydrogen (H) and one atom of oxygen (O) combine to form water (H2O).

Compounds are substances containing two or more elements.

Compounds are formed by chemical reactions and frequently have different properties than the original elements. Compounds are decomposed by a chemical reaction rather than separated by a physical one.  Solutions are homogeneous mixtures composed of two or more substances that have become one.  Mixtures contain two or more substances that are combined but have not reacted chemically with each other. Mixtures can be separated using physical methods, while compounds cannot.

A solution is a homogeneous mixture. A mixture is two or more different substances that are mixed together, but not combined chemically.

Homogeneous mixtures are those that are uniform in their composition. Solutions consist of a solute (the substance that is dissolved) and a solvent (the substance that does the dissolving). An example is sugar water. The solvent is the water and the solute is the sugar. The intermolecular attraction between the solvent and the solute is called solvation. Hydration refers to solutions in which water is the solvent. Solutions are formed when the forces between the molecules of the solute and the solvent are as strong as the forces holding the solute together. An example is that salt (NaCl) dissolves in water to create a solution. The Na+ and the Cl- ions in salt interact with the molecules of water and vice versa to overcome the intramolecular forces of the solute.

Elements are represented in upper case letters. If there is no subscript, it indicates there is only one atom of the element. Otherwise, the subscript indicates the number of atoms. In molecular formulas, elements are organized according to the Hill system. Carbon is first, hydrogen comes next, and the remaining elements are listed in alphabetical order. If there is no carbon, all elements are listed alphabetically. There are a couple of exceptions to these rules. First, oxygen is usually listed last in oxides.

Second, in ionic compounds the positive ion is listed first, followed by the negative ion. In CO2, for example, C indicates 1 atom of carbon and O2 indicates 2 atoms of oxygen. The compound is carbon dioxide. The formula for ammonia (an ionic compound) is NH3, which is one atom of nitrogen and three of hydrogen. H2O is two atoms of hydrogen and one of oxygen. Sugar is C6H12O6, which is 6 atoms of carbon, 12 of hydrogen, and 6 of oxygen. An atom is one of the most basic units of matter. An atom consists of a central nucleus surrounded by electrons. The nucleus of an atom consists of protons and neutrons. It is positively charged, dense, and heavier than the surrounding electrons. The plural form of nucleus is nuclei.  Neutrons are the uncharged atomic particles contained within the nucleus. The number of neutrons in a nucleus can be represented as 'N.'  Along with neutrons, protons make up the nucleus of an atom. The number of protons in the nucleus determines the atomic number of an element. Carbon atoms, for example, have six protons. The atomic number of carbon is 6. Nucleon refers collectively to neutrons and protons.  Electrons are atomic particles that are negatively charged and orbit the nucleus of an atom.  The number of protons minus the number of electrons indicates the charge of an atom.

The atomic number of an element refers to the number of protons in the nucleus of an atom. It is a unique identifier. It can be represented as Z. Atoms with a neutral charge have an atomic number that is equal to the number of electrons. Atomic mass is also known as the mass number. The atomic mass is the total number of protons and neutrons in the nucleus of an atom. It is referred to as 'A.' The atomic mass (A) is equal to the number of protons (Z) plus the number of neutrons (N). This can be represented by the equation A = Z + N. The mass of electrons in an atom is basically insignificant because it is so small.  Atomic weight may sometimes be referred to as 'relative atomic mass,' but should not be confused with atomic mass. Atomic weight is the ratio of the average mass per atom of a sample (which can include various isotopes of an element) to 1/12 of the mass of an atom of carbon-12.

Chemical properties are qualities of a substance which can't be determined by simply looking at the substance and must be determined through chemical reactions.  Some chemical properties of elements include: atomic number, electron configuration, electrons per shell, electronegativity, atomic radius, and isotopes.

In contrast to chemical properties, physical properties can be observed or measured without chemical reactions.  These include properties such as color, elasticity, mass, volume, and temperature.  Mass is a measure of the amount of substance in an object.   Weight is a measure of the gravitational pull of Earth on an object.  Volume is a measure of the amount of space occupied. There are many formulas to determine volume. For example, the volume of a cube is the length of one side cubed (a3) and the volume of a rectangular prism is length times width times height (l ∙ w

∙ h). The volume of an irregular shape can be determined by how much water it displaces.  Density is a measure of the amount of mass per unit volume.

The formula to find density is mass divided by volume (D=m/V). It is expressed in terms of mass per cubic unit, such as grams per cubic centimeter (g/cm3). 

Specific gravity is a measure of the ratio of a substance's density compared to the density of water.

Both physical changes and chemical reactions are everyday occurrences. Physical changes do not result in different substances. For example, when water becomes ice it has undergone a physical change, but not a chemical change. It has changed its form, but not its composition. It is still H2O. Chemical properties are concerned with the constituent particles that make up the physicality of a substance. Chemical properties are apparent when chemical changes occur. The chemical properties of a substance are influenced by its electron configuration, which is determined in part by the number of protons in the nucleus (the atomic number). Carbon, for example, has 6 protons and 6 electrons. It is an element's outermost valence electrons that mainly determine its chemical properties. Chemical reactions may release or consume energy.

Periodic Table

The periodic table groups elements with similar chemical properties together. The grouping of elements is based on atomic structure. It shows periodic trends of physical and chemical properties and identifies families of elements with similar properties. It is a common model for organizing and understanding elements. In the periodic table, each element has its own cell that includes varying amounts of information presented in symbol form about the properties of the element. Cells in the table are arranged in rows (periods) and columns (groups or families). At minimum, a cell includes the symbol for the element and its atomic number. The cell for hydrogen, for example, which appears first in the upper left corner, includes an 'H' and a '1' above the letter. Elements are ordered by atomic number, left to right, top to bottom.


In the periodic table, the groups are the columns numbered 1 through 18 that group elements with similar outer electron shell configurations. Since the configuration of the outer electron shell is one of the primary factors affecting an element's chemical properties, elements within the same group have similar chemical properties. Previous naming conventions for groups have included the use of Roman numerals and upper-case letters.

Currently, the periodic table groups are: Group 1, alkali metals; Group 2, alkaline earth metals; Groups 3-12, transition metals; Group 13, boron family;

Group 14; carbon family; Group 15, pnictogens; Group 16, chalcogens; Group 17, halogens; Group 18, noble gases.

In the periodic table, there are seven periods (rows), and within each period there are blocks that group elements with the same outer electron subshell (more on this in the next section).  The number of electrons in that outer shell determines which group an element belongs to within a given block.  Each row's number (1, 2, 3, etc.) corresponds to the highest number electron shell that is in use.  For example, row 2 uses only electron shells 1 and 2, while row 7 uses all shells from 1-7.

Atomic radii will decrease from left to right across a period (row) on the periodic table. In a group (column), there is an increase in the atomic radii of elements from top to bottom. Ionic radii will be smaller than the atomic radii for metals, but the opposite is true for non-metals. From left to right, electronegativity, or an atom's likeliness of taking another atom's electrons, increases. In a group, electronegativity decreases from top to bottom. Ionization energy or the amount of energy needed to get rid of an atom's outermost electron, increases across a period and decreases down a group. Electron affinity will become more negative across a period but will not change much within a group. The melting point decreases from top to bottom in the metal groups and increases from top to bottom in the non-metal groups.


Electrons

Electrons are subatomic particles that orbit the nucleus at various levels commonly referred to as layers, shells, or clouds. The orbiting electron or electrons account for only a fraction of the atom's mass. They are much smaller than the nucleus, are negatively charged, and exhibit wave-like characteristics. Electrons are part of the lepton family of elementary particles. Electrons can occupy orbits that are varying distances away from the nucleus, and tend to occupy the lowest energy level they can. If an atom has all its electrons in the lowest available positions, it has a stable electron arrangement. The outermost electron shell of an atom in its uncombined state is known as the valence shell. The electrons there are called valence electrons, and it is their number that determines bonding behavior. Atoms tend to react in a manner that will allow them to fill or empty their valence shells.

There are seven electron shells. One is closest to the nucleus and seven is the farthest away. Electron shells can also be identified with the letters K, L, M, N, O, P, and Q. Traditionally, there were four subshells identified by the first letter of their descriptive name: s (sharp), p (principal), d (diffuse), and f (fundamental).  The maximum number of electrons for each subshell is as follows: s is 2, p is 6, d is 10, and f is

14. Every shell has an s subshell, the second shell and those above also have a p subshell, the third shell and those above also have a d subshell, and so on.

Each subshell contains atomic orbitals, which describes the wave-like characteristics of an electron or a pair of electrons expressed as two angles and the distance from the nucleus. Atomic orbital is a concept used to express the likelihood of an electron's position in accordance with the idea of wave-particle duality.

Electron configuration: This is a trend whereby electrons fill shells and subshells in an element in a particular order and with a particular number of electrons. The chemical properties of the elements reflect their electron configurations. Energy levels (shells) do not have to be completely filled before the next one begins to be filled.  An example of electron configuration notation is 1s22s22p5, where the first number is the row (period), or shell. The letter refers to the subshell of the shell, and the number in superscript is the number of electrons in the subshell. A common shorthand method for electron configuration notation is to use a noble gas (in a bracket) to abbreviate the shells that elements have in common. For example, the electron configuration for neon is 1s22s22p6.

The configuration for phosphorus is 1s22s22p63s23p3, which can be written as [Ne]3s23p3. Subshells are filled in the following manner: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, and 7p.

Most atoms are neutral since the positive charge of the protons in the nucleus is balanced by the negative charge of the surrounding electrons. Electrons are transferred between atoms when they come into contact with each other. This creates a molecule or atom in which the number of electrons does not equal the number of protons, which gives it a positive or negative charge. A negative ion is created when an atom gains electrons, while a positive ion is created when an atom loses electrons. An ionic bond is formed between ions with opposite charges. The resulting compound is neutral.

Ionization refers to the process by which neutral particles are ionized into charged particles. Gases and plasmas can be partially or fully ionized through ionization.

Atoms interact by transferring or sharing the electrons furthest from the nucleus. Known as the outer or valence electrons, they are responsible for the chemical properties of an element. Bonds between atoms are created when electrons are paired up by being transferred or shared. If electrons are transferred from one atom to another, the bond is ionic. If electrons are shared, the bond is covalent. Atoms of the same element may bond together to form molecules or crystalline solids. When two or more different types of atoms bind together chemically, a compound is made. The physical properties of compounds reflect the nature of the interactions among their molecules. These interactions are determined by the structure of the molecule, including the atoms they consist of and the distances and angles between them.

Isotopes and Molecules

The number of protons in an atom determines the element of that atom.  For instance, all helium atoms have exactly two protons, and all oxygen atoms have exactly eight protons.  If two atoms have the same number of protons, then they are the same element. However, the number of neutrons in two atoms can be different without the atoms being different elements.  Isotope is the term used to distinguish between atoms that have the same number of protons but a different number of neutrons.  The names of isotopes have the element name with the mass number.  Recall that the mass number is the number of protons plus the number of neutrons.  For example, carbon-12 refers to an atom that has 6 protons, which makes it carbon, and 6 neutrons. In other words, 6 protons + 6 neutrons = 12.  Carbon-13 has six protons and seven neutrons, and carbon-14 has six protons and eight neutrons.  Isotopes can also be written with the mass number in superscript before the element symbol.  For example, carbon-12 can be written as ¹²C.

The important properties of water (H2O) are high polarity, hydrogen bonding, cohesiveness, adhesiveness, high specific heat, high latent heat, and high heat of vaporization. It is essential to life as we know it, as water is one of the main if not the main constituent of many living things. Water is a liquid at room temperature. The high specific heat of water means it resists the breaking of its hydrogen bonds and resists heat and motion, which is why it has a relatively high boiling point and high vaporization point. It also resists temperature change. Water is peculiar in that its solid-state floats in its liquid state. Most substances are denser in their solid forms. Water is cohesive, which means it is attracted to itself. It is also adhesive, which means it readily attracts other molecules. If water tends to adhere to another substance, the substance is said to be hydrophilic. Because of its cohesive and adhesive properties, water makes a good solvent. Substances, particularly those with polar ions and molecules, readily dissolve in water.

Electrons in an atom can orbit different levels around the nucleus. They can absorb or release energy, which can change the location of their orbit or even allow them to break free from the atom. The outermost layer is the valence layer, which contains the valence electrons. The valence layer tends to have or share eight electrons. Molecules are formed by a chemical bond between atoms, a bond that occurs at the valence level. Two basic types of bonds are covalent and ionic. A covalent bond is formed when atoms share electrons. An ionic bond is formed when an atom transfers an electron to another atom. A cation or positive ion is formed when an atom loses one or more electrons. An anion or negative ion is formed when an atom gains one or more electrons. A hydrogen bond is a weak bond between a hydrogen atom of one molecule and an electronegative atom (such as nitrogen, oxygen, or fluorine) of another molecule. The Van der Waals force is a weak force between molecules.

This type of force is much weaker than actual chemical bonds between atoms.

Reactions
Chemical reactions measured in human time can take place quickly or slowly. They can take fractions of a second or billions of years. The rates of chemical reactions are determined by how frequently reacting atoms and molecules interact. Rates are also influenced by the temperature and various properties (such as shape) of the reacting materials. Catalysts accelerate chemical reactions, while inhibitors decrease reaction rates. Some types of reactions release energy in the form of heat and light. Some types of reactions involve the transfer of either electrons or hydrogen ions between reacting ions, molecules, or atoms. In other reactions, chemical bonds are broken down by heat or light to form reactive radicals with electrons that will readily form new bonds. Processes such as the formation of ozone and greenhouse gases in the atmosphere and the burning and processing of fossil fuels are controlled by radical reactions.



Reactions
Chemical equations describe chemical reactions. The reactants are on the left side before the arrow and the products are on the right side after the arrow. The arrow indicates the reaction or change. The coefficient, or stoichiometric coefficient, is the number before the element, and indicates the ratio of reactants to products in terms of moles. The equation for the formation of water from hydrogen and oxygen, for example, is
2H2(g) + O2(g) → 2H2O(l). The 2 preceding hydrogen and water is the coefficient, which means there are 2 moles of hydrogen and 2 of water. There is 1 mole of oxygen, which does not have to be indicated with the number 1. In parentheses, g stands for gas, l stands for liquid, s stands for solid, and aq stands for aqueous solution (a substance dissolved in water). Charges are shown in superscript for individual ions, but not for ionic compounds. Polyatomic ions are separated by parentheses so the ion will not be confused with the number of ions. A. unbalanced equation is one that does not follow the law of conservation of mass, which states that matter can only be changed, not created. If an equation is unbalanced, the numbers of atoms indicated by the stoichiometric coefficients on each side of the arrow will not be equal. Start by writing the formulas for each species in the reaction. Count the atoms on each side and determine if the number is equal. Coefficients must be whole numbers. Fractional amounts, such as half a molecule, are not possible.

Equations can be balanced by multiplying the coefficients by a constant that will produce the smallest possible whole number coefficient. H2 + O2→ H2O is an example of an unbalanced equation. The balanced equation is 2H2 + O2 → 2H2O, which indicates that it takes two moles of hydrogen and one of oxygen to produce two moles of water.

One way to organize chemical reactions is to sort them into two categories: oxidation/reduction reactions (also called redox reactions) and metathesis reactions (which include acid/base reactions). Oxidation/reduction reactions can involve the transfer of one or more electrons, or they can occur as a result of the transfer of oxygen, hydrogen, or halogen atoms. The species that loses electrons is oxidized and is referred to as the reducing agent. The species that gains electrons is reduced and is referred to as the oxidizing agent. The element undergoing oxidation experiences an increase in its oxidation number, while the element undergoing reduction experiences a decrease in its oxidation number. Single replacement reactions are types of oxidation/reduction reactions. In a single replacement reaction, electrons are transferred from one chemical species to another. The transfer of electrons results in changes in the nature and charge of the species.

Single substitution, displacement, or replacement reactions are when one reactant is displaced by another to form the final product (A + BC
→ B + AC). Single substitution reactions can be cationic or anionic. When a piece of copper (Cu) is placed into a solution of silver nitrate (AgNO3), the solution turns blue. The copper appears to be replaced with a silvery-white material. The equation is 2AgNO3 + Cu → Cu (NO3)2 + 2Ag.

When this reaction takes place, the copper dissolves and the silver in the silver nitrate solution precipitates (becomes a solid), thus resulting in copper nitrate and silver. Copper and silver have switched places in the nitrate.

Combination, or synthesis, reactions: In a combination reaction, two or more reactants combine to form a single product (A + B → C).

These reactions are also called synthesis or addition reactions. An example is burning hydrogen in air to produce water. The equation is 2H2 (g) +
O2 (g) → 2H2O (l). Another example is when water and sulfur trioxide react to form sulfuric acid. The equation is H2O + 
SO3 → H2SO4.

Double displacement, double replacement, substitution, metathesis, or ion exchange reactions are when ions or bonds are exchanged by two compounds to form different compounds (AC + BD → AD + BC). An example of this is that silver nitrate and sodium chloride form two different products (silver chloride and sodium nitrate) when they react. The formula for this reaction is AgNO3 + NaCl → AgCl + NaNO3.

Double replacement reactions are metathesis reactions. In a double replacement reaction, the chemical reactants exchange ions but the oxidation state stays the same. One of the indicators of this is the formation of a solid precipitate. In acid/base reactions, an acid is a compound that can donate a proton, while a base is a compound that can accept a proton. In these types of reactions, the acid and base react to form a salt and water. When the proton is donated, the base becomes water and the remaining ions form a salt.

One method of determining whether a reaction is an oxidation/reduction or a metathesis reaction is that the oxidation number of atoms does not change during a metathesis reaction.

A neutralization, acid-base, or proton transfer reaction is when one compound acquires H+ from another. These types of reactions are also usually double displacement reactions. The acid has an H+ that is transferred to the base and neutralized to form a salt.

Decomposition (or desynthesis, decombination, or deconstruction) reactions; in a decomposition reaction, a reactant is broken down into two or more products (A → B + C).

These reactions are also called analysis reactions. Thermal decomposition is caused by heat. Electrolytic decomposition is due to electricity. An example of this type of reaction is the decomposition of water into hydrogen and oxygen gas. The equation is 2H2O → 2H2 + O2. 

Decomposition is considered a chemical reaction whereby a single compound breaks down into component parts or simpler compounds. When a compound or substance separates into these simpler substances, the byproducts are often substances that are different from the original. Decomposition can be viewed as the opposite of combination reactions. Most decomposition reactions are endothermic. Heat needs to be added for the chemical reaction to occur.

Separation processes can be mechanical or chemical, and usually involve re-organizing a mixture of substances without changing their chemical nature.

The separated products may differ from the original mixture in terms of chemical or physical properties. Types of separation processes include filtration, crystallization, distillation, and chromatography. Basically, decomposition breaks down one compound into two or more compounds or substances that are different from the original; separation sorts the substances from the original mixture into like substances.



Endothermic reactions are chemical reactions that absorb heat and exothermic reactions are chemical reactions that release heat.

Reactants are the substances that are consumed during a reaction, while products are the substances that are produced or formed. A balanced equation is one that uses reactants, products, and coefficients in such a way that the number of each type of atom (law of conservation of mass) and the total charge remains the same. The reactants are on the left side of the arrow and the products are on the right. The heat difference between endothermic and exothermic reactions is caused by bonds forming and breaking. If more energy is needed to break the reactant bonds than is released when they form, the reaction is endothermic.

Heat is absorbed and the environmental temperature decreases. If more energy is released when product bonds form than is needed to break the reactant bonds, the reaction is exothermic. Heat is released and the environmental temperature increases.

The collision theory states that for a chemical reaction to occur, atoms or molecules have to collide with each other with a certain amount of energy. A certain amount of energy is required to breach the activation barrier. Heating a mixture will raise the energy levels of the molecules and the rate of reaction (the time it takes for a reaction to complete). Generally, the rate of reaction is doubled for every 10 degrees Celsius temperature increase. However, the increase needed to double a reaction rate increases as the temperature climbs. This is due to the increase in collision frequency that occurs as the temperature increases. Other factors that can affect the rate of reaction are surface area, concentration, pressure, and the presence of a catalyst.

The particles of an atom's nucleus (the protons and neutrons) are bound together by nuclear force, also known as residual strong force. Unlike chemical reactions, which involve electrons, nuclear reactions occur when two nuclei or nuclear particles collide. This results in the release or absorption of energy and products that are different from the initial particles. The energy released in a nuclear reaction can take various forms, including the release of kinetic energy of the product particles and the emission of very high energy photons known as gamma rays. Some energy may also remain in the nucleus. Radioactivity refers to the particles emitted from nuclei as a result of nuclear instability. There are many nuclear isotopes that are unstable and can spontaneously emit some kind of radiation. The most common types of radiation are alpha, beta, and gamma radiation, but there are several other varieties of radioactive decay.

Inorganic and Organic

The terms inorganic and organic have become less useful over time as their definitions have changed. Historically, inorganic molecules were defined as those of a mineral nature that were not created by biological processes. Organic molecules were defined as those that were produced biologically by a 'life process' or 'vital force.' It was then discovered that organic compounds could be synthesized without a life process. Currently, molecules containing carbon are considered organic. Carbon is largely responsible for creating biological diversity, and is more capable than all other elements of forming large, complex, and diverse molecules of an organic nature. Carbon often completes its valence shell by sharing electrons with other atoms in four covalent bonds, which is also known as tetravalence.

The main trait of inorganic compounds is that they lack carbon. Inorganic compounds include mineral salts, metals and alloys, non-metallic compounds such as phosphorus, and metal complexes. A metal complex has a central atom (or ion) bonded to surrounding ligands (molecules or anions). The ligands sacrifice the donor atoms (in the form of at least one pair of electrons) to the central atom. Many inorganic compounds are ionic, meaning they form ionic bonds rather than share electrons. They may have high melting points because of this. They may also be colorful, but this is not an absolute identifier of an inorganic compound. Salts, which are inorganic compounds, are an example of inorganic bonding of cations and anions. Some examples of salts are magnesium chloride (MgCl2) and sodium oxide (Na2O). Oxides, carbonates, sulfates, and halides are classes of inorganic compounds. They are typically poor conductors, are very water soluble, and crystallize easily. Minerals and silicates are also inorganic compounds.

Two of the main characteristics of organic compounds are that they include carbon and are formed by covalent bonds. Carbon can form long chains, double and triple bonds, and rings. While inorganic compounds tend to have high melting points, organic compounds tend to melt at temperatures below 300° C. They also tend to boil, sublimate, and decompose below this temperature. Unlike inorganic compounds, they are not very water soluble.

Organic molecules are organized into functional groups based on their specific atoms, which helps determine how they will react chemically. A few groups are alkanes, nitro, alkenes, sulfides, amines, and carbolic acids. The hydroxyl group (-OH) consists of alcohols. These molecules are polar, which increases their solubility. By some estimates, there are more than 16 million organic

Nomenclature refers to the manner in which a compound is named. First, it must be determined whether the compound is ionic (formed through electron transfer between cations and anions) or molecular (formed through electron sharing between molecules). When dealing with an ionic compound, the name is determined using the standard naming conventions for ionic compounds. This involves indicating the positive element first (the charge must be defined when there is more than one option for the valency) followed by the negative element plus the appropriate suffix. The rules for naming a molecular compound are as follows: write elements in order of increasing group number and determine the prefix by determining the number of atoms. Exclude mono for the first atom. The name for CO2, for example, is carbon dioxide. The end of oxygen is dropped and 'ide' is added to make oxide, and the prefix 'di' is used to indicate there are two atoms of oxygen.


Acids and Bases

The potential of hydrogen
(pH) is a measurement of the concentration of hydrogen ions in a substance in terms of the number of moles of H+ per liter of solution. All substances fall between 0 and 14 on the pH scale. A lower pH indicates a higher H+ concentration, while a higher pH indicates a lower H+ concentration. Pure water has a neutral pH, which is 7. Anything with a pH lower than water (0-7) is considered acidic. Anything with a pH higher than water (7-14) is a base. Drain cleaner, soap, baking soda, ammonia, egg whites, and sea water are common bases. Urine, stomach acid, citric acid, vinegar, hydrochloric acid, and battery acid are acids. A pH indicator is a substance that acts as a detector of hydrogen or hydronium ions. It is halochromic, meaning it changes color to indicate that hydrogen or hydronium ions have been detected.

When they are dissolved in aqueous solutions, some properties of acids are that they conduct electricity, change blue litmus paper to red, have a sour taste, react with bases to neutralize them, and react with active metals to free hydrogen. A weak acid is one that does not donate all of its protons or disassociate completely. Strong acids include hydrochloric, hydriodic, hydrobromic, perchloric, nitric, and sulfuric. They ionize completely. Superacids are those that are stronger than 100 percent sulfuric acid. They include fluoroantimonic, magic, and perchloric acids. Acids can be used in pickling, a process used to remove rust and corrosion from metals. They are also used as catalysts in the processing of minerals and the production of salts and fertilizers. Phosphoric acid (H3PO4) is added to sodas and other acids are added to foods as preservatives or to add taste.



When they are dissolved in aqueous solutions, some properties of bases are that they conduct electricity, change red litmus paper to blue, feel slippery, and react with acids to neutralize their properties. A weak base is one that does not completely ionize in an aqueous solution, and usually has a low pH. Strong bases can free protons in very weak acids.

Examples of strong bases are hydroxide compounds such as potassium, barium, and lithium hydroxides. Most are in the first and second groups of the periodic table. A superbase is extremely strong compared to sodium hydroxide and cannot be kept in an aqueous solution. Superbases are organized into organic, organometallic, and inorganic classes. Bases are used as insoluble catalysts in heterogeneous reactions and as catalysts in hydrogenation.

Some properties of salts are that they are formed from acid base reactions, are ionic compounds consisting of metallic and nonmetallic ions, dissociate in water, and are comprised of tightly bonded ions. Some common salts are sodium chloride (NaCl), sodium bisulfate, potassium dichromate
(K2Cr2O7), and calcium chloride (CaCl2).

Calcium chloride is used as a drying agent, and may be used to absorb moisture when freezing mixtures. Potassium nitrate (KNO3) is used to make fertilizer and in the manufacture of explosives. Sodium nitrate (NaNO3) is also used in the making of fertilizer. Baking soda (sodium bicarbonate) is a salt, as are Epsom salts [magnesium sulfate (MgSO4)]. Salt and water can react to form a base and an acid. This is called a hydrolysis reaction.

A buffer is a solution whose pH remains relatively constant when a small amount of an acid or a base is added. It is usually made of a weak acid and its conjugate base (proton receiver) or one of its soluble salts. It can also be made of a weak base and its conjugate acid (proton donator) or one of its salts. A constant pH is necessary in living cells because some living things can only live within a certain pH range. If that pH changes, the cells could die. Blood is an example of a buffer. A pKa is a measure of acid dissociation or the acid dissociation constant. Buffer solutions can help keep enzymes at the correct pH. They are also used in the fermentation process, in dyeing fabrics, and in the calibration of pH meters. An example of a buffer is

HC2H3O (a weak acid) and NaC2H3O2
(a salt containing the C2H3O2- ion).


General Concepts

Lewis formulas: These show the bonding or nonbonding tendency of specific pairs of valence electrons. Lewis dot diagrams use dots to represent valence electrons. Dots are paired around an atom. When an atom forms a covalent bond with another atom, the elements share the dots as they would electrons. Double and triple bonds are indicated with additional adjacent dots.

Methane (CH4), for instance, would be shown as a C with 2 dots above, below, and to the right and left and an H next to each set of dots. In structural formulas, the dots are single lines.

Kekulé diagrams: Like Lewis dot diagrams, these are two-dimensional representations of chemical compounds. Covalent bonds are shown as lines between elements. Double and triple bonds are shown as two or three lines and unbonded valence electrons are shown as dots.

Molar mass: This refers to the mass of one mole of a substance (element or compound), usually measured in grams per mole (g/mol).
This differs from molecular mass in that molecular mass is the mass of one molecule of a substance relative to the atomic mass unit (amu).

Atomic mass unit (amu) is the smallest unit of mass, and is equal to 1/12 of the mass of the carbon isotope carbon-12. A mole (mol) is a measurement of molecular weight that is equal to the molecule's amu in grams.

For example, carbon has an amu of 12, so a mole of carbon weighs 12 grams. One mole is equal to about 6.0221415 x 1023 elementary entities, which are usually atoms or molecules. This amount is also known as the Avogadro constant or Avogadro's number (NA). Another way to say this is that one mole of a substance is the same as one Avogadro's number of that substance. One mole of chlorine, for example, is 6.0221415 x 1023 chlorine atoms. The charge on one mole of electrons is referred to as a Faraday.

The kinetic theory of gases assumes that gas molecules are small compared to the distances between them and that they are in constant random motion. The attractive and repulsive forces between gas molecules are negligible. Their kinetic energy does not change with time as long as the temperature remains the same. The higher the temperature is, the greater the motion will be. As the temperature of a gas increases, so does the kinetic energy of the molecules. In other words, gas will occupy a greater volume as the temperature is increased and a lesser volume as the temperature is decreased. In addition, the same amount of gas will occupy a greater volume as the temperature increases, but pressure remains constant. At any given temperature, gas molecules have the same average kinetic energy. The ideal gas law is derived from the kinetic theory of gases.

Charles's law: This states that gases expand when they are heated. It is also known as the law of volumes.

Boyle's law: This states that gases contract when pressure is applied to them. It also states that if temperature remains constant, the relationship between absolute pressure and volume is inversely proportional.

When one increases, the other decreases. Considered a specialized case of the ideal gas law, Boyle's law is sometimes known as the Boyle-Mariotte law.

The ideal gas law is used to explain the properties of a gas under ideal pressure, volume, and temperature conditions. It is best suited for describing monatomic gases (gases in which atoms are not bound together) and gases at high temperatures and low pressures. It is not well-suited for instances in which a gas or its components are close to their condensation point. All collisions are perfectly elastic and there are no intermolecular attractive forces at work. The ideal gas law is a way to explain and measure the macroscopic properties of matter. It can be derived from the kinetic theory of gases, which deals with the microscopic properties of matter. The equation for the ideal gas law is PV = nRT, where 'P' is absolute pressure, 'V' is absolute volume, and 'T' is absolute temperature. 'R' refers to the universal gas constant, which is 8.3145 J/mol Kelvin, and 'n' is the number of moles.