Chemical Bonding

Question 1

Define electronegativity

Answer 1

Power of an atom to attract electrons to itself

Question 2

Describe the change in electronegativity.

Answer 2

Change in electronegativity = Biggest EN - Smallest EN

Change in EN = 0 - 0.4 - Pure covalent bond
Change in EN = 0.5 - 1.9 - Polar covalent bond
Change in EN > 1.9 - Ionic bond

Question 3

Describe the factors that affect electronegativity.

Answer 3

Across the period:
- Increase in protons
- Greater nuclear charge
- Larger electronegativity value

Down the group:
- Atomic radius increases
- Shielding effect increases
- Lower electronegativity value

Question 4

Define ionic bonding

Answer 4

The electrostatic attraction between oppositely charged ions

Question 5

Describe the properties of ionic compounds.

Answer 5

High melting points and boiling points - strong electrostatic forces of attraction between ions
Can only conduct electricity when molten/aqueous - when solid, ions fixed in a crystal lattice and cannot carry charge
Brittle
Soluble in water

Question 6

Define metallic bonding

Answer 6

Electrostatic attraction between positive ions and delocalised electrons

Question 7

Describe the properties of metallic compounds.

Answer 7

Malleable and ductile - ions can slide over each other easily
Good conductors of electricity
High melting and boiling points

Question 8

Define polar covalent bonds

Answer 8

Bond occurs when there is an unequal distribution of charge

Question 9

Define covalent bonding

Answer 9

Electrostatic attraction between the nuclei of two atoms and shared pairs of electrons

Question 10

Define sigma bonds

Answer 10

Formed by direct overlap of orbitals between bonding atoms
Sigma stronger than Pi - greater overlap

s overlaps s
s overlaps p
p overlaps p

Question 11

Define pi bonds

Answer 11

Formed by sideways overlap of adjacent p orbitals above and below the sigma bond

p overlaps p

Question 12

Define single, double and triple bonds in terms of sigma and pi bonds.

Answer 12

Single - sigma bond
Double - sigma + pi bond
Triple - sigma + pi bond

Question 13

Define pure covalent bonds

Answer 13

Bond occurs when there is an equal distribution of charge

Question 14

Define dative covalent bonds

Answer 14

One atom shares its lone pair of electrons with another - only way it forms is if the atom has an incomplete octet.

Question 15

Define VSEPR

Answer 15

The properties of molecules depend on both the bonds between the atoms, and their molecular geometry.

VSEPR (valence-shell, electron-pair repulsion) theory states that repulsion between the sets of valence-shell electrons surrounding an atom causes these sets to be oriented as far apart from each other as possible.

Question 16

What are the 2 factors that affect VSEPR?

Answer 16

1. The number of areas of negative charge (i.e the bonding pairs)
   NB - whether it is a single, double or triple bond, it counts as one area of negative charge
2. The number of lone pairs of electrons (Lone pairs repel other electrons, and take up space around the central atom, but the name is based on the shape of the atoms only)

Question 17

Define steric number

Answer 17

Number of atoms bonded to the central atom + number of lone pairs on the central atom

Question 18

Describe the A.X.E model.

Answer 18

A - central atom
X - number of atoms attached to the central atom
E - number of lone pairs of electrons on the central atom

Question 19

What are the 7 types of shapes of molecules + bond angles?

Answer 19

Linear - 180 degrees
Bent/angular - 104.5 degrees
Trigonal planar - 120 degrees
Trigonal pyramidal - 107 degrees
Tetrahedral - 109.5 degrees
Trigonal bipyramidal - 90 degrees
Octahedral

Question 20

Define hypervalency

Answer 20

Some atoms can have more than 8 electrons surrounding them