3 STRUCTURE AND BONDING

Question 1

what is ionic bonding? when does it occur?

Answer 1

transfer of electrons; occurs when electronegativity difference is above 1.9

Question 2

what is covalent bonding? when does it occur?

Answer 2

sharing of electrons; occurs when electronegativity difference is below 1.9

Question 3

how can you estimate melting pt?

Answer 3

based off of size - larger atoms have lower melting pts

Question 4

how to determine formal charge?

Answer 4

based off how many electrons originally belonged to element

Question 5

which elements can have expanded octets?

Answer 5

3rd period and below can have expanded octets

Question 6

best structures of a compound … ? (related to formal charge)

Answer 6

have the least formal charge on central atom

Question 7

what are resonance structures? and what should be noted bout them?

Answer 7

correct lewis structures differing only in position of electrons (bonding and non-bonding); must remember that electrons are waves not dots/particles and that neither structures actually exist

Question 8

what does a higher avg bond order indicate?

Answer 8

a higher avg bond means shorter and stronger bonds

Question 9

what are the molecular geometry types and with how many regions of electron groups do they correspond with?

Answer 9

linear(1); trigonal planar(3); tetrahedral(4); trigonal bipyramidal(5); octahedral(6)

Question 10

what are the three deficiencies of valence bonding theory that molecular orbital theory covers?

Answer 10

1. VB takes a localized approach to bonding and fails to explain resonance theory. 2. VB tells us nothing bout relative energies of electron in molecule. 3. VB fails to predict diamagnetism/paramagnetism; paramagnetic compounds have at least one unpaired electron

Question 11

in molecular orbitals, what is bonding based on?

Answer 11

bonding is based on the wave behaviour of electron

Question 12

if two 1s wavefunctions combine constructively…?

Answer 12

both wavelengths in same phase; no new nodes are made; sigma1s bonding orbital

Question 13

if two 1s wavefunctions combine destructively…?

Answer 13

wavelengths in different phases; new node made; combine to form sigma1s antibonding orbital

Question 14

what are the principles of molecular orbital theory?

Answer 14

the number of molecular orbitals = the number of atomic orbitals. MOs form best from AOs of similar energy. bonding lower than antibonding. must obey pauli exclusion principle and hunds rule

Question 15

what does MO bonding order help determine?

Answer 15

if a molecule will exist or not (exists = stable); 0 means it doesnt exist. the higher the bonding order the higher the stability

Question 16

what is the problem with MOs from 2p atomic orbitals?

Answer 16

three 2p per atom but only one orbital can overlap with that of another atom

Question 17

what are the principles of the valence bond theory?

Answer 17

covalent bonds formed by orbital overlap; electrons in bond are localized; orbitals may hybridize before bond formation

Question 18

what is the order of intermolecular forces, weakest to strongest?

Answer 18

dispersion, dipole-dipole, hydrogen bonding, ionic

Question 19

what is dispersion?

Answer 19

temporary dipoles caused by electron movement; increases with surface area

Question 20

what is dipole-dipole force?

Answer 20

permanent dipole caused by electron movement; increases with surface area

Question 21

what is hydrogen bonding and what atoms is this between?

Answer 21

a type of dipole bonding; between H & N,O,F

Question 22

what is more important in melting pt than boiling?

Answer 22

symmetry is more important. a symmetrical figure has higher melting pt ignoring intermolecular forces.

Question 23

what does boiling do? how to compare boiling pts?

Answer 23

it breaks intermolecular forces! stronger intermolecular forces means a higher breaking pt. more surface area means lower boiling pt. branching has more surface area

Question 24

what notation is used for VESPR?

Answer 24

AXmEn. m=bonding n=nonbonding