Covalent Bonding

Question 1

What is a ‘pure’ sybstance?

Answer 1

Uniform composition

Cannot be separated into simpler substances by physical means

Question 2

Define hetero/homogeneous mixtures

Answer 2

Hetero - components can be seen

Homogenous - uniform composition

Question 3

Element anion suffix

Answer 3

-ide

Eg. H- = hydride
S2- = sulfide

Question 4

What is an oxoanion?

Answer 4

Oxygen bonded (1 or more double bonds) to a central atom of a polyatomic ion

Eg. CO3^2-
End in -ate
Carbonate

Question 5

Relative energy of bonded atoms vs non-bonding

Answer 5

Bonded have LOWER energy

Due to stronger attractive forces between -ve and +ve particles

Question 6

Define covalent bond

Answer 6

Electron pairs between bonded atoms attracted to both NUCLEI (positive particles, NOT CATIONS) of bonded atoms

Question 7

Is ionic bond formation exo or endo?

Answer 7

EXO

Driven by ions coming together (lattice formation)

Question 8

Bond dipole moment units of measurement

Answer 8

Debye

Question 9

Describe the morse curve

Answer 9

Energy vs distance between two atoms

Starts high, falls below x-axis, increases and tends to 0

At the minimum point, atoms approach each other and lose potential energy, electron pair bond formed

Question 10

Why do C, O, N form multiple bonds but larger atoms do not?

Answer 10

Multiple bonds require overlap of particular e- clouds

Better overlap, stronger bond when atoms are SMALL

Question 11

Lewis diagrams order of atoms general rule

Answer 11

The more electronegative atom is usually outer

Eg. N2O has N-N-O

Question 12

Formal charge rules

Answer 12

Sum of formal charges = overall charge

1. Assign an atom bonding + 1/2 nonbonding e-
2. LESS than #valence e- = POSITIVE charge (more positive than isolated atom)
   MORE = NEG

Question 13

Why use formal charges to assess plausability

Answer 13

Relative plausability of lewis structures.

Separating charge requires energy, hence LOWER formal charges is a better representation of the species

Question 14

Define resonance form

Answer 14

Energetically equivalent (same # bonding and nonbonding e-) structures differ only in e- position

Question 15

What is the hybrid structure?

Answer 15

Has -ve charge delocalised, equivalent bonds

like all resonance forms combined

Of LOWER energy (less reactive) dud to delocalisation

Question 16

VSEPR define

Answer 16

e- pair domains about an atom occupies regions in space which are AS FAR APART as possible to minimise repulsion

Question 17

four electron areas possible shapes

Answer 17

all occupied = tetrahedral
3 occupied = trigonal pyramid
2 occupied = bent 109.5

Question 18

5 electron areas possible shapes and angles

Answer 18

all occupied = trigonal bipyramidal
4 occupied = see saw
3 occupied = t-shaped
90 and 120 degree angles

Question 19

6 electron areas possible shapes and angles

Answer 19

all occupied = octahedral
5 occupied = square pyramidal
4 = square planar

Question 20

regular bond angles apply ONLY IF…

Answer 20

all e- domains are equivalent.

non-bonding e- pair domains occupy MORE space.

Question 21

What property does bond strength affect?

Answer 21

the reactivity (energy required to break bond)

Question 22

trend in the strength of bond in relation to atom size

Answer 22

bonds between SMALLER atoms are SHORTER and STRONGER

Question 23

strength of multiple bonds in relation to single

Answer 23

multiple = SHORTER and STRONGER than single.

Question 24

define covalent bond in terms of orbitals

Answer 24

merging / overlap of orbitals and pairing of electron spins

Question 25

sigma bond

Answer 25

SINGLE BOND.

two e- in an orbital with cylindrical symmetry about the bond axis.
e- density concentrated between the nuclei of the bonding atoms. (bonding e- are localised)

eg. singly occupied pz orbital and s or another pz
(pz is taken as the orientation along bond axis)

Question 26

pi bond

Answer 26

DOUBLE bond

formed by overlap of orbitals in a side-by-side fashion, lobes either side of the internuclear axis.
e- density concentrated above and below the plane of the nuclei of bonding atoms.

eg. two singly occupied px or py orbitals

Question 27

triple bond (in terms of pi and sigma)

Answer 27

1 sigma, 2 pi bonds

Question 28

what is a hybrid orbital?

Answer 28

blended valence orbital, so they are energetically equivalent

linear combination (addition)

Question 29

number of hybrid orbitals =

Answer 29

number of atomic orbitals combined.

eg. 1s + 3p makes 4 identical sp3 hybrid orbitals

Question 30

hybrid and shape - how do decide what hybrid set to use

Answer 30

#hybrid orbitals required at a particular atom = 
#sigma bonds + # non-bonding e- pairs

Question 31

how do hybrid orbitals form sigma bonds?

Answer 31

can overlap with hybrid OR s-orbitals on adjacent atoms.

Question 32

overall e- density at an atom =

Answer 32

sum of e- densities of the occupied orbitals.

atom w/ hybridised orbitals has the same overall e- density as unhybridised orbitals.

Question 33

what are temporary dipoles

Answer 33

Van der Waals forces
e- cloud in adjacent uncharged particles induces temporary dipoles when particles are close (liquid)

present in condensed phase of EVERY molecule

larger e- cloud = polarised to greater extent = stronger attractive forces (hence Tb increases as size increases)

Question 34

permanent dipoles

Answer 34

exist in a polar molecule with partial charge, when there is an electronegative element (O, N, halogen) present.

Question 35

hydrogen bonding

Answer 35

when H bonded to O, N or F, a very strong dipole is formed, making H very strongly (partially) positive.

stronger than temporary/permanent dipoles, apt 1/10 the strength of a covalent bond