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By the end of this topic, students will be able to:
Electron configuration is the arrangement of electrons in an atom. It is a way of describing the energy levels and orbitals that electrons occupy. The electron configuration of an atom determines its chemical properties, such as its reactivity and the types of compounds it can form.
The electron configuration of an atom can be represented using a notation system called the Aufbau principle. This principle states that electrons occupy the lowest available energy levels, and that each energy level can hold a maximum of two electrons with opposite spins.
The Aufbau principle can be used to write the electron configuration of an atom. For example, the electron configuration of carbon is 1s² 2s² 2p². This means that the first energy level (1s) is occupied by two electrons, the second energy level (2s) is occupied by two electrons, and the second energy level (2p) is occupied by two electrons.
Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. This means that isotopes have the same atomic number but different atomic masses.
Isobars, on the other hand, are atoms of different elements that have the same mass number (i.e., the sum of protons and neutrons). This means that isobars have different atomic numbers but the same atomic mass.
For example, carbon-12 and carbon-13 are isotopes of carbon, while chlorine-35 and argon-40 are isobars.
The periodic table is a tabular arrangement of elements that are grouped according to their atomic number and electron configuration. The periodic table can be used to identify and describe the electron configuration of elements.
The periodic table is arranged in a way that elements with similar electron configurations are placed in the same group (vertical column). This means that elements in the same group have similar chemical properties.
Write the electron configuration of the element sodium (Na).
To write the electron configuration of sodium, we need to follow the Aufbau principle. Sodium has an atomic number of 11, which means it has 11 electrons.
The first energy level (1s) can hold a maximum of two electrons, so we start by filling this energy level with two electrons.
Next, we move to the second energy level (2s), which can hold a maximum of two electrons. We fill this energy level with two electrons.
Finally, we move to the second energy level (2p), which can hold a maximum of six electrons. We fill this energy level with six electrons.
The electron configuration of sodium is therefore 1s² 2s² 2p?.
Identify the following as isotopes or isobars:
To answer this question, we need to recall the definition of isotopes and isobars.
Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. Isobars, on the other hand, are atoms of different elements that have the same mass number (i.e., the sum of protons and neutrons).
Carbon-12 and carbon-13 are isotopes because they are atoms of the same element (carbon) with the same number of protons (6) but different numbers of neutrons (12 and 13, respectively).
Chlorine-35 and argon-40 are isobars because they have the same mass number (35 and 40, respectively) but are atoms of different elements.
What is the electron configuration of the element oxygen (O)?
A) 1s² 2s² 2p? B) 1s² 2s² 2p? C) 1s² 2s² 2p? D) 1s² 2s² 3s²
Correct answer: B) 1s² 2s² 2p?
Why the distractors fail: A) is incorrect because oxygen has 8 electrons, not 4. C) is incorrect because oxygen has 8 electrons, not 8 in the 2p orbital. D) is incorrect because oxygen has 8 electrons, not 4 in the 3s orbital.
Which of the following is an example of an isotope?
A) Carbon-12 and carbon-13 B) Chlorine-35 and argon-40 C) Oxygen-16 and oxygen-32 D) Nitrogen-14 and nitrogen-28
Correct answer: A) Carbon-12 and carbon-13
Why the distractors fail: B) is incorrect because chlorine-35 and argon-40 are isobars, not isotopes. C) is incorrect because oxygen-16 and oxygen-32 are isotopes, but the question asks for an example of an isotope. D) is incorrect because nitrogen-14 and nitrogen-28 are isotopes, but the question asks for an example of an isotope.
Write the electron configuration of the element chromium (Cr).
A) 1s² 2s² 2p? 3s² 3p? 4s² 3d? B) 1s² 2s² 2p? 3s² 3p? 4s² 3d? C) 1s² 2s² 2p? 3s² 3p? 4s² 3d? D) 1s² 2s² 2p? 3s² 3p? 4s² 3d?
Correct answer: A) 1s² 2s² 2p? 3s² 3p? 4s² 3d?
Why the distractors fail: B) is incorrect because chromium has 24 electrons, not 25. C) is incorrect because chromium has 24 electrons, not 26. D) is incorrect because chromium has 24 electrons, not 25.
A) Isotopes: oxygen-16 and oxygen-32, Nitrogen-14 and nitrogen-28 B) Isobars: oxygen-16 and oxygen-32, Nitrogen-14 and nitrogen-28 C) Isotopes: oxygen-16 and oxygen-32, Isobars: Nitrogen-14 and nitrogen-28, Chlorine-35 and argon-40 D) Isobars: oxygen-16 and oxygen-32, Isotopes: Nitrogen-14 and nitrogen-28, Chlorine-35 and argon-40
Correct answer: C) Isotopes: oxygen-16 and oxygen-32, Isobars: Nitrogen-14 and nitrogen-28, Chlorine-35 and argon-40
Why the distractors fail: A) is incorrect because oxygen-16 and oxygen-32 are isotopes, but nitrogen-14 and nitrogen-28 are isobars. B) is incorrect because oxygen-16 and oxygen-32 are isotopes, and nitrogen-14 and nitrogen-28 are isobars. D) is incorrect because oxygen-16 and oxygen-32 are isotopes, and chlorine-35 and argon-40 are isobars.
Write the electron configuration of the element copper (Cu).
Why the distractors fail: B) is incorrect because copper has 29 electrons, not 28. C) is incorrect because copper has 29 electrons, not 27. D) is incorrect because copper has 29 electrons, not 26.
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