AP Chemistry · Summary

Unit 1 summary

1. Grams to moles is $n = \frac{m}{M}$; moles to particles is $N = n \times N_A$. Always say moles of what, molecules or atoms.
2. Average atomic mass is the weighted average of the isotope masses; turn peak heights into fractions of the total first.
3. For an empirical formula, use mole ratios, never mass ratios: grams to moles, divide by the smallest, then clear any fraction.
4. Fill subshells 1s 2s 2p 3s 3p 4s 3d 4p; remove electrons from the highest shell first, so transition metals lose 4s before 3d.
5. In a photoelectron spectrum, each peak is a subshell, its position is the binding energy and its height is the number of electrons.
6. Across a period, more protons in the same shell means smaller atoms and higher ionization energy; down a group, an added shell means larger atoms and lower ionization energy.
7. A big jump in successive ionization energies marks the first core electron, and so counts the valence electrons.