lecture 1 recap lecture

Question 1

what elements count as main group elements

Answer 1

elements in the s and p block

Question 2

what is Zeff

Answer 2

the effective nuclear charge felt by the outermost electron

Question 3

what rules do we use to predict Zeff

Answer 3

slaters rules

Question 4

equation for Zeffective

Answer 4

Zeff = Z - shielding constant

where Z is the nuclear charge

Question 5

Zeff trendssss

Answer 5

across a period ➡️: Zeff increases
down a group⬇️: Zeff decreases

Question 6

Zeff trends explained

Answer 6

as u go across a period,, the number of protons and electrons increase by1.

e- are in the same or different shells which makes them unale to shield the outermost e- from the increase in nuclear charge.

Question 7

which orbital is the best at shielding

Answer 7

s>p>d>f

bc its closer to the nuc + has a larger shielding ability.

Question 8

how does Zeff change as atom radius//size increases

Answer 8

as the atom gets larger,,, the Zeff decreases

theyre inversely proportional

Question 9

how does Zeff affect atom size

Answer 9

as Zeff increases the atoms size decreases.

due to larger attraction between the outer electron and the nucleus.

Question 10

what are the 2 different contractions seen in the periodic table used to explain trends seen in the atomic radii

Answer 10

d block contraction
and lanthanide // f block contractions

Question 11

explain the contractions

Answer 11

atoms below each other may have very similar atomic radii // size.

this is due to added e- being put in the d or f orbital (lots of space) and so they cannot shield the outermost electron from the added nuclear charge

this causes the atom to be much smaller than expected.

Question 12

what is electronegativity

Answer 12

it is the ability of an atom in a molecule to attract e- towards itself.

Question 13

what element is the most electronegative

Answer 13

Flourineeee

Question 14

different definitions for electronegativity

Answer 14

allred rochow
pauling
muliken

Question 15

muliken electronegativity scale

Answer 15

based on the mean of the sum of IE and EA + constants

Question 16

pauling electronegativity scale

Answer 16

based on bond strength
heteronuclear bonds are stronger than homonuclear bonds due to the electronegativity difference

and therefore increase in ionic character.

Question 17

allred rochow electronegativity scale

Answer 17

based on Zeff and covalent radius

Zeff being effective nuclear charge.

Question 18

allred rochow little arrow diagram thing

Answer 18

as the atom size increases
its electronegactivity decreases

Question 19

what electronegativity explain

Answer 19

it can explain the e- distribution is a bond

Question 20

if a bond is polarised itttt

Answer 20

its a polar bond
has an uneven distribution of e-
theres an electronegatvity diffference between the 2 atoms in the molecule.

Question 21

the more elctronegative moelcule will have a

Answer 21

partial negactive charge

Question 22

the less electronegative molecule will have a

Answer 22

partial positive charge

Question 23

when is a bond ionic

Answer 23

when there is a large electronegativity difference

one that is more than 2 units

it forms A+ and B-

no partial +/-

Question 24

electronegativity has what symbol

Answer 24

X

Question 25

are the X values the same for the same moelcule

Answer 25

nope they can change depending on the chemical environment its O.S,,, bonding partners,, EWDG, EDG

Question 26

if X can change,, what are the given vales of X

Answer 26

the elements X in an average chemical environment

Question 27

describe the reaction with NMe3 and BH3

Answer 27

N lone pair attacks the B which has an empty p orbital NMe3 is now (+) as it has given away its lone pair. HOWEVER,, N is still more elctronegative than C, so it has a partial negative charge. the B is now (-) as its accepted e-. however B is less electronegaative than H,, and so has a partial positive charge.

Question 28

describe the bond strengths trends of homonuclear bonds

Answer 28

down a group = weaker bond = less effective overlap of orbitals due to larger atom size

Question 29

homonuclear bonds that go against the trends

Answer 29

the CNF homonuclear bonds theyre no small that their lone pairs repel eachother giving a decrease in efficient orbital overlap which weakens the bond. lone pair lone pair repulsion

Question 30

are heteronuclear or homonuclear bonds stronger

Answer 30

usually heteronuclear bonds bc theres a difference in electronegatvity so more ionic character bond strength is proportional to (Xa - Xb)^2 the bond is stronger but could be more reactive due to being polarised

Question 31

is NF3 thermodynamically stable

Answer 31

yessss the N-F bond is stronger than the homonuclear NN or FF bonds due to the difference in electronegativity + ionic character.

Question 32

is NCl3 a stronger or weaker bond than NF3

Answer 32

its a weaker bond as there is no electronegativity difference. meaning less ionic character. as the bond isnt polarised due to the same X values.

Question 33

what do we consider to deduce ionic bond strength

Answer 33

we consider lattice energy cation + anion + ionic radius

Question 34

what is lattice energy proportional to

Answer 34

q+ q- /// r+ + r-

Question 35

VSEPR

Answer 35

when we can predict the shape of a molcule by the number of valence e- pairs it has.