Topic 2: Bonding & Sturcture

Question 1

Ionic bond

Answer 1

Strong electrostatic attraction between two oppositely charged ions
cation +, anion -

Question 2

Ionic Bond Strength Factors

Answer 2

Greater charge = stronger bond (more electrons transferred)
Smaller ionic radii = stronger bond as electrostatic attraction gets weaker with distance
Higher charge density = stronger bond

Question 3

Ionic Radii Trends

Answer 3

Increases as you go down a group
Ionic radius of isoelecreonic electrons decreases across a period -> higher electrostatic attraction so more effective nuclear charge

Question 4

Isoelectronic Ions

Answer 4

Same electronic configuration
E,g N3-, O2-

Question 5

Giant Ionic Lattice

Answer 5

same basic unit repeating
ions are electrostatically attracted to the opposite charge in all directions

Question 6

Properties of Ionic Bonds

Answer 6

High melting point
Soluble in water but not in non-polar solvents: proves it contains ions
Conducts electricity when aqueous or molten but not when solid as ions are free to move
Brittle: if it is same ions are on top of one another strong repulsion causes bonds to break

Question 7

Covalent Bonds

Answer 7

Strong electrostatic attraction between a pair of shared electrons and two positively charged nuclei

Question 8

Covalent Bond Length

Answer 8

Distance at which forces are balanced
Nuclei are attracted to area of e- density but repel each other

Question 9

Covalent Bond Enthalpy

Answer 9

Energy needed to break one molecule of a bond, directly proportional to bond strength
More shared pairs -> higher e- density -> stronger attraction -> higher bond enthalpy
Stronger enthalpy = shorter bond

Question 10

Dative Covalent Bonds

Answer 10

When one atom donates both electrons to a bond

Question 11

Shapes of Molecules

Answer 11

Depend on number of electron pairs in outer shell of central atom
Lone / bonded pairs

Question 12

Electron repulsion: angles

Answer 12

Bonded/bonded has highest bond angle, then lone/bonded then lone/lone
Bond angle is smaller because lone/lone is larger
Atoms are pushed closer to minimise repulsion

Question 13

Linear

Answer 13

2 electron pairs, none lone
180°

Question 14

Trigonal Planar

Answer 14

3 electron pairs, none lone
120°

Question 15

Non-linear, “bent”

Answer 15

3 electron pairs, one lone (e.g SO2)
119°
4 electron pairs, 2 lone (e.g H2O)
104.5°

Question 16

Tetrahedral

Answer 16

4 electron pairs, none lone
109.5°

Question 17

Trigonal pyramidal

Answer 17

3 electron pairs, 1 lone
107°

Question 18

Giant Covalent Structures

Answer 18

Huge lattices of covalently bonded atoms with much stronger electrostatic forces of attraction

Question 19

Properties of Giant Covalent Structures

Answer 19

Very high melting points
Extremely hard
Good thermal conductors as vibrations can travel easily through stiff lattices
Insoluble as they don’t contain ions
Cannot conduct electricity as they have no delocalised e- or ions

Question 20

Graphite

Answer 20

CAN CONDUCT ELECTRICITY
shares 3/4 e- so each atom has one delocalised that can move between layers (lubricant)
GRAPHENE is a sheet of carbon, can conduct as delocalised moves along sheet
Strong, light, transparent

Question 21

Giant Metallic Structures

Answer 21

Layers of positive metal ions separated by layers of electrons
Metallic Bonding: +ve metal ions are electrostatically attracted to delocalised electrons

Question 22

Properties of Giant Metallic Structures

Answer 22

High melting point
Good electrical & thermal conductors
Malleable, ductile
Insoluble

Question 23

Electronegativity

Answer 23

Ability of an atom to attract the bonded pair of electrons in a covalent bond
Increases across periods (nuclear charge increases and atomic radii decreases)
Decreases down groups

Question 24

Polarisation of bonds

Answer 24

Occurs due to differences in electronegativity, causes a dipole
Non-polar if e-ns are similar or identical e.g homonuclear molecules
Polar: uneven spread of e- in bond -> bonded pair will be closer to most electronegative
Higher difference: more ionic

Question 25

Polar Molecules

Answer 25

In simple molecules a polar bond makes whole thing permanent dipole (polar molecule) If there are several bonds: 1) non-polar if they are on opposite sides -> cancel out 2) polar if they are roughly on same side

Question 26

London Forces

Answer 26

Type of intermolecular forces (weaker than covalent) Induced dipole-dipole interaction: e- moves to one side so nucleus is attracted to e- cloud Overall effect makes atoms attracted to each other in a lattice -> simple molecular structure More molecular surface contact means stronger forces and higher mp

Question 27

Permanent dipole-dipole bonds

Answer 27

Occur in addition to London Forces Form polar molecules Higher energy to overcome than just london

Question 28

Hydrogen Bonding

Answer 28

Strongest type of intermolecular force If H is covalently bonded to N, O, F (which draw e- away from H) Very polarised bond & H has high charge density so H atoms form weak bonds to lone pairs

Question 29

Group 7 hydrides

Answer 29

HF has high boiling point From HCl to HI permanent dipole-dipole decrease but is overridden as number of e- increases so there are stronger London forces which cause bp to increase Group 6 hydrides follow similar trends

Question 30

Why does ice float?

Answer 30

lattice structure in ice aims for maximum n of hydrogen bond, “wasting space” -> ice is less dense than water As ice melts, some bonds are broken so lattice breaks down