AP Chemistry Unit 1 Thou Shalt Not Forget

1: When reading measurements from a graduated instrument(e.g. graduate cylinder, burette, ruler)…

you must estimate by reading in between the graduated markings. This gives you one more sig. fig. in your measurement.

BONUS: 1 - When measuring with a burette…

measure by subtracting NOT by reading bottom-up

2: Ranking measuring devices from least to most precise…

beaker, graduated cylinder, volumetric flasks, burette

BONUS: 2 - The volumetric flask has…

only ONE line on it to measure one specific volume

3: Density =

mass/volume, you can use it in stoichiometry problems to convert between mass and volume

4: The percent composition by mass for a pure compound …

does not change

5: Mass spectroscopy graphs …

depict the atomic masses and relative abundances of isotopes

6: Coulomb’s Law

the attractive force between an atom’s protons and electrons is directly proportional to the number of protons (effective charge = Z eff) and indirectly proportional to the square of the distance between the nucleus and the electrons

7: When an electron is in a higher energy level…

it is farther away from the nucleus and therefore has less Coulombic attraction to the nucleus and is therefore easier to remove(i.e. it has a lower 1st ionization energy)

8: Moving across a row on the periodic table…

Z eff increases, therefore the valence electrons are more attracted to the nucleus, therefore the atomic radius decreases and the ionization energy increases

9: When reading a PES graph, the higher the peak…

the more electrons there are in that sublevel

10: When reading a PES graph, a larger binding energy means…

the electrons are closer to the nucleus

11: According to Aufbau: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ . However, AP…

Doesn’t care if you put 4s before or after 3d ( or 5s before 4d, etc.) as long as you have the right number of electrons in each sublevel

12: When writing the electron configuration for a cation…

remove the valence electrons first…starting with the highest p-orbital (if there is one) and then the highest s-orbital. After that you can remove d-orbital electrons if necessary.

13: Isotopes of an element have…

the same number of protons, but different numbers of neutrons, and hence a different mass number

14: Elements of the same group (vertical columns) have…

similar chemical and physical properties

15: On the periodic table…

metals are on the left side of the zig-zag line and nonmetals are on the right side of this line

16: Cations(+) are…

smaller than their atoms since you are removing valence electrons that are farther from the nucleus

17: Anions(-) are…

larger than their atoms since adding extra electrons increases electron-electron repulsions without increasing nuclear charge

18: Percent yield =

experimental mass/theoretical mass

19: percent error =

(experimental - theoretical)/theoretical

H₂ O₂ N₂ Cl₂ Br₂ I₂ F₂ are…

diatomic elements. This property only applies when they are by themselves. When they are in a compound, their number of atoms can vary