Topic 4 - Chemical Bonding & Structure

Question 1

Giant Covalent Structure

Answer 1

Very hard but brittle.

Very high m.p. and b.p.

Do not conduct in any state.

Insoluble.

Question 2

Giant Ionic Lattice

Answer 2

Hard but brittle.

High m.p. and b.p.

Conduct when molten or aqueous, but not as solids.

Soluble

Question 3

Giant Metallic Structure

Answer 3

Malleable (not brittle)

M.p. and b.p. dependent on no. of valence e-.

Good conductivity.

Insoluble, (some metals react with water)

Question 4

Molecular Lattice

Answer 4

Usually soft and malleable unless hydrogen bonded.

Low m.p. and b.p.

Do not conduct in any state.

Often soluble in non-aqueous solvents, unless they can hydrogen bond to water

Question 5

Allotropes

Answer 5

Different crystalline forms of the same element - Carbon

Question 6

Bond polarity

Answer 6

Polarity = difference in electronegativity between elements.

The greater the difference, the greater the polarity.

Question 7

Pi bond (π)

Answer 7

Formed by the sideways overlap of p orbitals

Electron densities = above and below a line drawn through the two nuclei.

Double bonds = one π bond
Triple bonds = two π bonds (perpendicular to each other)

Question 8

Sigma bond (σ)

Answer 8

Formed by overlap of atomic orbitals from two different atoms along the line drawn through the two nuclei

Electron densities concentrated along the line.

Single, double, triple bonds = one σ bond.

Question 9

Covalent bond

Answer 9

Bonding by the sharing of electrons.

The electrons are shared and attracted by both nuclei resulting in a bi-directional bond two atoms.

Question 10

Dative bond (co-ordinate bond)

Answer 10

A bond in which both electrons come from one of the atoms.

Question 11

Ionic bond

Answer 11

A bond where electrons are transferred from one atom to another - form ions with complete outer shells.

Ionic compound + and – ions = attracted (to each other) by electrostatic force between them

Build up into a strong lattice.

Have high m.p.

Ionic bonds occur between elements with a great difference (>1.8) in electronegativity

Question 12

Van der Waal’s / London Dispersion forces

Answer 12

Temporary dipole forces due to momentary unevenness in spread of electrons.
Weakest of intermolecular forces.

Question 13

Conductivity

Answer 13

The extent to which a substance can conduct electricity. Must possess electrons / ions = free to move.

Question 14

Delocalization

Answer 14

The sharing of one electron pair by more than two atoms.

Question 15

Dipole-Dipole

Answer 15

Permanent electrostatic forces of attraction between polar molecules.

Stronger than van der Waals’
Weaker than H-Bonding

Question 16

Hydrogen bonding

Answer 16

Hydrogen attached to a highly electronegative element (N, F, or O) is bonded to another highly electronegative element (N, F, or O).

Stronger than dipole:dipole forces & van der Waals’

Question 17

Hybridization

Answer 17

The mixing of atomic orbitals to create new orbitals of the same energy.

Question 18

Metallic bonding

Answer 18

Valence electrons in metals become detached from the individual atoms = metals consist of a closely packed lattice of + ions in a ‘sea’ of delocalized electrons.

Forces of attraction are between ions + electrons (not between the ions themselves) = metals are malleable and ductile.

Question 19

Molecular polarity

Answer 19

Depends on both the bond polarity and the symmetry.

Question 20

Resonance Structures

Answer 20

Structures that arise from the possibility to draw multiple bonds in different positions equivalently.
(delocalization)

Question 21

Solubility

Answer 21

The extent to which one substance dissolves in another.

Question 22

VSEPR theory

‘Valence Shell Electron Pair Repulsion’ theory

Answer 22

States that pairs of electrons arrange themselves around the central atom so that they are as far apart from each other as possible.
Greater repulsion between lone pair of electrons than bonded pairs.