U1 chemical bonds

Question 1

Intramolecular bonding

Answer 1

bonding within molecules

These are: ionic, metallic and covalent

Question 2

Ionic bonding

Answer 2

Electrostatic forces of attraction between pos and neg ions, usually between a metal and non-metal

Question 3

Metallic bonding

Answer 3

Electrostatic force of attraction between pos metal ions and a ‘sea’ of electrons (delocalised electrons)

Question 4

Covalent bonding

Answer 4

Atoms share pairs of electrons. A covalent bond is the result of 2 pos nuclei being held together by common attraction for a shared pair of electrons.

Question 5

Polar covalent bonding

Answer 5

Polar covalent bonds are formed when the attraction of the atoms for the pair of bonding electrons is different.

Delta pos and delta neg notation can be used to indicate partial charges on atoms, which give rise to a dipole. The attraction of the atoms for the pair of electrons is the electronegativity and is given in data booklet.

Question 6

Non-polar/ Pure Covalent bonding

Answer 6

Formed when electrons shared equally between atoms (same electronegativity)

Question 7

The bonding continuum

Answer 7

The difference in electronegativities between bonded atoms gives an indication of ionic character. The larger the difference, the more polar the bond will be. If the difference is large, then the movement of bonding electrons from the element of lower electronegativity to the element of higher electronegativity is complete, resulting in the formation of ions.

Question 8

Polar molecule

Answer 8

Compounds with polar bonds will form polar molecules provided the molecule is not symmetrical (such as water)

Question 9

Non-polar molecule

Answer 9

Compounds with non-polar bonds will form non-polar molecules). Symmetrical compounds with polar bonds such as CO2 and CH4 will form non-polar molecules.

Question 10

Intermolecular forces

Answer 10

Bonding between molecules

Known as Van der Waals forces.

Several types: LDF, permanent dipole- permanent dipole, hydrogen bonding).

Question 11

LDF

Answer 11

Can operate between all atoms and molecules.

Much weaker than all other types

They are formed because of electrostatic attraction between temporary dipoles and induced dipoles caused by the movement of electrons in atoms and molecules.

Strength is related to number of electrons within an atom or molecule.

Question 12

PDP-PDP

Answer 12

Additional electrostatic forces of attraction between polar molecules.

They are stronger than LDF for molecules with similar electron numbers.

Question 13

Hydrogen bonding

Answer 13

Consists of a hydrogen bonded to an atom of strongly electronegative element such as Fl, O, N are highly polar.

Hydrogen bond is stronger than other forms of PDP-PDP but weaker than a covalent bond.

Question 14

High Tm

Answer 14

Giant structures

Metallic lattice: solid & conduct
Ionic lattice: liquid and aq conduct
Covalent network: non-conduction under all conditions

Question 15

Low Tm

Answer 15

molecular structures

Covalent molecular: very low Tm, insoluble in water

Polar covalent: Higher Tm, some soluble in water

Question 16

LDF higher Tb

Answer 16

stronger the forces of attraction between molecules. Therefore, the energy required for evaporation would appear to be determined by mass or no of electrons in molecule

Question 17

Properties of water

Answer 17

Density less than ice - due to expanding when frozen forming open type lattice

high surface tension

relatively high viscosity

Question 18

All ionic lattices and polar covalent molecules are

Answer 18

soluble in water and other polar solvents

insoluble in non-polar solutions

vice-versa - ‘like dissolves like’