Unit 1

molarity, electron config, ionization energy, photon spectroscopy, periodic trends

what does mass spectroscopy do and why

separates components of a sample by mass in order to determine # isotopes present, atomic mass of each isotope, and relative abundance of each isotope

what is an isotope’s relative abundance

% of atoms in sample with the specific atomic mass of that isotope (# neutrons + # protons)

formula for avg atomic mass of an element

∑(relative abundance %)(atomic mass)

how to find empirical formula

1. change all elements from percentages to mass (grams)

2. find each elements’ # of moles using molar mass

3. divide each mole value by the lowest mole value

4. round to whole numbers

how to find molecular formula

1. find mass of total empirical formula of particle

2. (GIVEN molar mass of particle)/emp.mass => factor

3. multiply empirical formula by factor

shells vs subshells vs orbitals

shells: 1, 2, 3, 4…

subshells: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p…

orbitals: hold a max. of 2 e- each

Coulomb’s Law

F ∝ q₁q₂/(r²)

Aufbau Principle (e- configuration)

e- are added to lowest subshells (eg. s then p)

Hund’s Rule (e- configuration)

each subshell should have one e- before they’re paired up

Pauli Exclusion Principle (e- configuration)

can’t have 2 arrows pointing in same direction when drawing orbital diagram

The four exceptions to e- configuration and why

Cu, Ag, Cr, Mo

b/c they are one electron short of a completely half full or full subshell, so one electron from the prev. shell moves to that shell

When filling in an orbital diagram, what direction should the first arrow (represents an e-) be?

up

what do photoelectron spectroscopy graphs show and how can i use them?

the number of e- vs. ionization energies

typically there are ‘spikes’ for each subshell, so given that the 1s subshell always has 2e-, u can figure out identity of the element by finding the furthest spike and seeing how many e- it has

*note: the ionization energy increases towards the LEFT, not the right, since the highest value of ionization energy is for the innermost e-

particle movement: microwave vs. infrared vs. ultraviolet spectroscopy

rotational; vibrational; translational (transitions in electronic energy levels since e- move from ground state to excited state)

effective nuclear charge and shielding

ENC: the net charge on valence e- by protons

Shielding decreases the effective nuclear charge bc the inner e- shield nuclear attraction from valence e-

Ionization Energy and IE Trends

the energy required to remove the outermost e- from the gas form of an atom

• decreases down a group/column: as you go down the table, the atoms have more e- levels/shells so e- are further from the nucleus and have a lower coulombic attraction. shielding also occurs

• increases across a period/row: atoms gain one more proton and the atomic radius decreases, which results in greater coulombic attraction

ionization energy exceptions

Group 2 and Group 13

• Ex: Beryllium (left) and Boron (right): B requires less IE than Be to remove an e- bc the outermost e- is in the 2p orbital, which is further from the nucleus so it takes less energy to remove.

Group 15 and Group 16

• Ex: Nitrogen and Oxygen: O requires less IE than N bc the electrons in O are sharing the 2p orbital so they have greater repulsions, which makes it easier to remove an e-.

atomic radius trends across PT

• decreases across a period: increasing number of protons increases the effective nuclear charge

• increases down a group: there are more e- shells

electron affinity and trends

amount of energy released when an atom gains an e-

• increases across a group bc the valence shell of the atom is filled

• decreases down GROUP 1 ONLY bc the additional e- is less attracted to nucleus so would release less energy

electronegativity and trends

the ability to attract shared e- (polar covalent bond: unequal sharing of electrons)

• increases across a period as number of atoms increases

• decreases down a group bc there are more electron shells and shielding

• fluorine is the most electronegative element

ionic bond

a bond that involves the transfer of e- from the lesser electronegative atom to the more electronegative one