Middle School Physical Science: Atoms - Inside the Atom — Flashcards

Atoms are the basic building blocks of matter. An atom consists of a central nucleus that is surrounded by one or more negatively charged electrons. The nucleus is positively charged and contains one or more relatively heavy particles known as protons and neutrons. 

Sometimes atoms lose or gain electrons and become ions. Ions are particles that have a positive or negative charge.    
That's because they do not have the same number of electrons as protons. If atoms lose electrons, they become positive ions, or cations. If atoms gain electrons, they become negative ions, or anions. 

Example: A fluorine atom has nine protons and nine electrons, so it is electrically neutral.    
If a fluorine atom gains an electron, it becomes a fluoride ion with a negative charge of minus one.    
Some atoms of the same element differ in their number of neutrons. These atoms are called isotopes. Many isotopes occur naturally. Usually one or two isotopes of an element are the most stable and common.

Different isotopes of an element generally have the same chemical properties. That's because they have the same numbers of protons and electrons. Isotopes are generally named for their mass number.

For example, carbon atoms with the usual 6 neutrons have a mass number of 12 (6 protons + 6 neutrons = 12), so they are called carbon-12. Carbon atoms with 7 neutrons have an atomic mass of 13 (6 protons + 7 neutrons = 13). These atoms are the isotope called carbon-13.