4.1 Ionic compounds / ionic bonds

Question 1

Define chemical bond

Answer 1

CHEMICAL BOND: stable association between atoms

Question 2

Why elements in Group 14 do not form ions?

Answer 2

They have 4 e in outer shell - do not gain/lose e - not form ions - energetically unfavourable to transfer e - from covalent bonds

Question 3

Define polyatomic ion

Answer 3

POLYATOMIC ION: ion made from more than one atom which together experience loss/gain of e and carry charge

Examples: NH₄⁺, NO₃^-, HCO₃^-

Question 4

Formation of ionic compounds

Answer 4

Includes ionisation - e transferred between atoms - metal loses e - non-metal gains e

Both Na⁺ and Cl^- have noble gas configuration

Question 5

Define ionic bond

Answer 5

IONIC BOND: association created by electrostatic forces between two oppositely charged ions

Question 6

Define ionic compound

Answer 6

IONIC COMPOUND: ions held together by electrostatic forces called ionic bonds

Question 7

Lattice structure in ionic compounds

Answer 7

Ionic compounds form 3D rystalline structure - ionic lattice

Lattice geometry depend on ions

Question 8

What does coordination number determine

Answer 8

Coordination number determines how many ions surround a particular ion in lattice structure

In NaCl - each Na⁺ is surrounded by 6 Cl^- -> coordination number 6 / each Cl^- by 6 Na⁺

Question 9

What does formula unit determine

Answer 9

Formula unit (empirical formula) determines the ration between the different ions which form an ionic lattice

Question 10

Define lattice energy

Answer 10

LATTICE E: measure of strength of attraction between ions within a lattice

Question 11

Trends of melting/boiling points of ionic compounda

Answer 11

Tendency of high melting/boiling points as electrostatic attractions between ions are strong - require a alot of E to be broken

The greater ion charge - the more E needed to break - the higher melting/boiling points

Question 12

Define volatility

Answer 12

VOLATILITY: term used to describe the tendency of a substance to vapourise

Ionic com - low volatility or non-volatile

Question 13

Define solubility

Answer 13

SOLUBILITY: property of how easy a solid substance becomes dispersed through a liquid to form a solution

Question 14

How ionic compounds dissolve>

Answer 14

Become hydrated by water molecules - partial charge of water molecules are attracted to ions of opposite charge in lattice - dislodge ions from their positions - solid dissolves

Question 15

How are ions called whoch dissolve in other solvents tha water

Answer 15

Solvated

Ex. hexane - non-polar will no dissolve ionic compound

Like dissolves like

Question 16

Define electrical conductivity

Answer 16

ELECTRICAL CONDUCTIVITY: ability of a coumpound to conduct electricity - depends on ions - charge

Ionic compounds cannot conduct electricity at solid state - ions mus form - solutions/molten

Question 17

Define brittleness

Answer 17

BRITTLENESS: property of compounds to shatter when force is applied

Ionic crystalls are brittle - forces make ionic bonds split

Question 18

Define binary compound

Answer 18

BINARY COMPOUND: a compound which is composed of only two elements

Question 19

How can a tendency of two elemnts to form an ionic compound be evaluated

Answer 19

On EN values - measure of ability of an tom to attract e in a covalent bond (using Pauling scale)

Difference >1.8 - mainly ionic compound

Distinction between ionic and covalent compound is spectrical (not binary)