Bonding

Question 1

Allotrope

Answer 1

Occur when an element can exist in different crystalline forms, such as in carbon, which can exist as graphite, buckminsterfullerene (bucky ball) and diamond. Diamond is exceptionally hard because there is no plane of weakness in the molecule made up of sp3 hybridized carbon atoms. In graphite, the carbon atoms are sp2 hybridized. Remaining e- after the three σ bonds, are delocalized, resulting in the fact that graphite is an excellent lubricant and a good conductor of electricity.

Question 2

Bond length and strength

Answer 2

Depends on strength of attraction that two nuclei have for the shared e-. Generally, the stronger the bond, the shorter its length.

Question 3

Bond polarity

Answer 3

A polarity caused by a difference in electronegativity between the elements. The greater the difference, the greater the polarity.

Question 4

Bond, π

Answer 4

Pi bond. A radial bond formed by the sideways overlap of p orbitals with e- densities concentrated above and below a line drawn through the two nuclei. Double bonds have one π bond, while triple bonds have two which are perpendicular to each other.

Question 5

Bond, σ

Answer 5

Sigma bond. An axial bond formed by the head on/head-to-head overlap of atomic orbitals from two different atoms along the line drawn through the two nuclei, with e- densities concentrated along the line. Single, double and triple bonds have one σ bond.

Question 6

Covalent bond

Answer 6

Bonding by the sharing of e-. The e- are shared and attracted by both nuclei resulting in a directional bond between the two atoms.

Question 7

Dative bond

Answer 7

A bond in which both e- come from one of the atoms. Also known as coordinate bond.

Question 8

Ionic bond

Answer 8

A bond by which e- are transferred from one atom to another to form ions with complete outer shells. In an ionic compound the + and - ions are attracted to each other by the electrostatic force between them, and build up into a strong lattice. Have relatively high m.p. Ionic bonds occur between elements with a great difference (>1.8) in electronegativity.

Question 9

Conductivity

Answer 9

The extent to which a substance can conduct electricity. Must possess e- or ions that are free to move.

Question 10

Delocalization

Answer 10

The sharing of a single e- pair by more than two atoms.

Question 11

Forces, dipole-dipole

Answer 11

Permanent electrostatic forces of attraction between polar molecules. Stronger than van der Waals’.

Question 12

Forces, Hydrogen bonding

Answer 12

Occurs when hydrogen is bonded directly to a highly electronegative element (N, F, or O). Stronger than dipole:dipole forces.

Question 13

Forces, van der Waal’s

Answer 13

Temporary dipole forces due to momentary unevenness in spread of e-. Weakest of intermolecular forces. Increase with increasing molar mass.

Question 14

Hybridization

Answer 14

The combination of orbitals to create new orbitals that are more energetically feasible for bonding.

Question 15

Lewis structure

Answer 15

Diagram showing arrangement of e- in a molecule. Usually only shows valence shells.

Question 16

Metallic bonding

Answer 16

The valence e- in metals become detached from the individual atoms so that the metals consist of a closely packed lattice of + ions in a ‘sea’ of delocalized e-. Forces of attraction are between ions and e- and not between the ions themselves, which means that metals are malleable and ductile.

Question 17

Molecular polarity

Answer 17

Depends on both the bond polarity and the symmetry.

Question 18

Resonance hybrid

Answer 18

Structures that arise from the possibility to draw a multiple bond in different positions equivalently. Can be better explained by delocalization.

Question 19

Solubility

Answer 19

The extent to which one substance dissolves in another. ‘Like tends to dissolve like.’

Question 20

VSEPR theory

Answer 20

Valence Shell Electron Pair Repulsion theory. States that pairs of e- arrange themselves around the central atom so that they are as far apart from each other as possible. Greater repulsion between lone pair of e- than bonded pairs.