Bonding

Question 1

Ionic bonds

Answer 1

This is a bond formed when one atom transfers one or more electrons to another atom, resulting in electrostatic attraction between cations and anions

Question 2

Covalent bonds

Answer 2

Pair of electrons with opposite spin shared between two atoms, with each atom giving one electron

• -> The electrons in the pair repeal one another, but this is overcome by their attraction to both nuclei
• -> If atoms get too close together, the nuclei and their inner electrons will repel those of the other atom so that the bond has a certain length

Question 3

Coordinate bond

Answer 3

Both electrons forming the bond pair come from the same atom/group of atoms
E.g. boron trichloride + ammonia

–> Always polar, since the atom giving both electrons to the bond cannot completely lose its rights over one electron, forming a partial d+ on donor and partial d- on acceptor

Question 4

Metallic

Answer 4

Lattice of positive ions is held together by a ‘sea’ of delocalised electrons given up by each atom

Question 5

Electronegativity

Answer 5

Measure of how strongly an atom in a compound attracts the pair of electrons in a bond

• -> No electronegativity: pure, non-polar covalent
• -> Polar covalent: there is a separation of charge between one end of the atom and the other; one is d- and the other d+ e.g. HCl

Question 6

Polarization of an anion

Answer 6

The electric distortion of the shape of a polarisable anion by a cation, to produce some covalent character in ionic bonds e.g. LiCO3

This depends on

(1) The charge density of the positive ion: as charge density increases polarizing ability increases
(2) The size of the positive ion: as the size of the ion decreases, the polarizing ability increases
(3) The size of the negative ion: as the size of the negative ion increases, the polarizing ability increases

Question 7

Intermolecular interactions

VAN DER WAALS forces

(1) Dipole-dipole interactions
(2) Induced dipole-temporary dipole interactions

HYDROGEN BONDS

Answer 7

VDW: weak intermolecular forces that exist BETWEEN all atoms and molecules [i.e. covalent] and include dipole-dipole interactions and induced-dipole-induced-dipole interactions

(1) Dipole-dipole interactions
Where molecules have a permanent dipole, due a difference in electronegativity between the atoms e.g. HCl, there are permanent attractive forces between the molecule

(2) Induced dipole-temporary dipole interactions
Molecules with no dipole show intermolecular bonding because, instantaneous dipoles may induce and equal and opposite dipole in a neighbouring molecule causing momentary attraction
–> More electrons [molecular mass] = more induced dipole interactions
–> Straight chain > branch chain because more points of contact for vdw forces to act between the surfaces of the molecule

–> In neutral/non polar molecules/atoms, these instantaneous dipoles average out over time to give 0 permanent dipole moment

Question 8

Intramolecular bonds

Answer 8

Strong bonding WITHIN atoms and molecules and governs reactivity

Ionic, covalent, metallic

Question 9

Hydrogen bonds

Answer 9

Intermolecular bonding force that occurs between molecules that contain H atoms bonded to -F, -N or -O [very electronegative + have lp electrons]

Ionic > covalent > intramolecular > HB > vdw

• -> STRENGTH: H atom is small and can form an electrostatic bond when sandwiched between 2 electronegative elements. HB strongest when 3 atoms are in a straight line
• -> LENGTH OF BONDS: internal bonds shorter than external bonds
• -> SOLUBILITY: HB can dissolve other molecules. E.g. in ethanol, the hydrogen atom of the -OH group can hydrogen bond with water molecules

Question 10

VSEPR

Answer 10

The shape adopted by a molecule or ion is that which keeps repulsive forces to a minimum. Bonds will push each other as far as possible to reduce repulsion.