Chem Exam 3 Review

Z*

Net or effective nuclear charge that is “felt” by an e^- of interest (attraction between nucleus and electron

Valance Electrons

They do not screen each other effectively

Comparing 3s vs 3p Z*

3s has a greater Z* due to the greater number of secondary maxima, which allows electron to penetrate the core e^- density 

Electron Orbital Energy  (En,l)

Is just the negative/opposite of ionization energy 

Z* Left to Right

Increase as only valance electrons are being added and they don’t screen effectively, so the atom with the greater amount of protons will have a greater Z* due to Columbic force 

Z* Going Down

Z* increases but not as much as the increase of protons is overpowered by the additional filled core levels as n increases, overpowering P, and the valance e^- are higher in energy 

Ionization energy

The main energy required to remove (eject) electron from the highest energy orbital in a ground gaseous state atom/ion 

1st IE

X(g) → X^+(g) + e^- (ejected with 0 KE), becomes the threshold

IE going across

Increases in Z*, En,l becomes more negative, so IE increases

IE going down

Increases n (dominant factor), En,l becomes less negative, IE decreases

2nd IE

Z* increases for everyone, needs more nergy and all orbital energy decreases X^+(g) → X²+(g) + e^-(ejected with 0 KE)

2nd IE > 1st IE

For a given series of elements, IEn is always greatest when the electron being removed has the largest Z* and smallest n, espically when there are no core electrons 

Electron Affinity

Minimum energy required to remove the highest energy valance electron from X^-(g) in its ground state, X^- → X(g) +e^- (ejected with 0 KE and always reported as neutral atom) Follows the trend of IE and noble gases are exceptions because X^- is just next subshell and don’t need that much energy to remove electron

Atomic Radii Across

Increasing Z*, coulombic attraction increases b/w E^- and nucleus, electron orbital contracts, size is smaller

Atomic Radii Down

Increases n, spatial extent of orbital increases, size increases

Ionic Radii

Anion: Z* down means radius increases and opposite for cation

Electronegativity

The ability of an atom in a molecule to attract e^- to itself and way from neighobring atoms: (IE+EA)/2, same trend on periodic table 

Bond Strength

Larger Bond Order, mean shorter bond length, and Greater BDE (the average amount of energy required to break a bond, and overal stronger bond 

BDE

Is equal to -zeropoint level (total energy of the bond)

Repulsion-order Rule

Lone pair (2x) > lone + bond > bond pair (2x)

SN=5

Has axial position and equatorial position, move electronegative atoms in axial position to reduce repulsion 

SN=6

2nd lone pair should be not touching for less repulsion 

Localized Electron Model (LEM)

Model that describe how electrons are arranged in molecules, assume that electrons are localized in the ground state, accounts for wave nature of electrons and results in molecular geometry

HYbridization

(Adding two waves on the same atom): sp (180), sp² (120), sp³ (109) 

Sigma Bonds

Form when two orbitals overlap directly head-on b/w two atoms, straight along line connecting the nuclei, the electron density is all in one continuous region, no empty plane node 

Pi bonds

From from side-by-side overlap, which leaves a node right between the atoms

Bond Rotation

Pi bonds Overlap of unhybridized p-orbitals, When the p-orbitals are no longer parallel, their sideways overlap is lost, which effectively breaks the pi bond. Breaking this bond requires a significant amount of energy. So under number conditions, double bonds are essentially rigid

Failures of LEM

1.Use of Localized bonds when electrons are delocalized 2. Can’t do exited states due to hybridization 3. Predicts the wrong magnetic properties as it assumes all electrons are localized pairs, hiding unpaired electrons that exist. 

Molecular Orbital Theory (MOT)

Formed by mixing (sp) atomic orbitals on different atoms, describe ground stae and exited states of molecules/ions

Bonding

Mixings aos constructive interference, greaters dot density around nuclei and 2nd is in between the two atoms

Anti-bonding

result from destructive interference, where they cancel out is node (planar and perpendicular to bond) and also 2nd greatest density be-hide the nuclei (opposite of bonding) .. also change signs 

Bond Order of MO

1/2(Bonding - Antibonding) (not possible with bond less than 0)

1st row homonucleuar diatomics

congi: (sigma 1s)^n and has 1s and sigma 1s

2nd order diagram

Li2-N2 and ions, starts with sigma 2s, but then top starts with pi 2px pi 2py, then sigma 2pz and then antibonding pi 2px

1st order diagram

O2-Ne2 and ions, starts with sigma 2s, but then top starts with sigma 2px, then pi 2px pi 2py, then antibonding pi 2px

Homo 

Highest Energy Occupied Molecular Orbital 

LUMO

Lowest Unoccupied Molecular Orbital (always have this down)  

Homonuclear

Non-polar covalent bond, has an equal electronegativity 

Polar covalent bond

When subtraction electronegativity, it is either less than or equal to 2 

In bonding, with not symmetric bonding…

Make the large molecular the more electronegative one as they contribute more (stronger attraction for electrons)  to bonding and the opposite for anti-bonding (electronegative one is closer(lower) to bonding and further form anti-bonding) 

When combing LEM/MO

LEM to describe localized electrons via sigma frame work, and MOT to describe delocalized electrons via pi framework 

Use Combined MOT + LEM Model when.. 

some electrons are localized and some are delocalized 

Paramagnetic

Has Unpaired electrons Ia single electron in orbital) attracted to magnets

Diamagnetic

All electrons are paired, all electrons are in a pair , repelled by magnets

Lewis Structures Resonance Bond Order

(total number of bonds)/(number of bonding position in that is possible)