Chemistry IGCSE - Atoms, elements and compounds continued

Structure of metallic bonding

electrostatic attraction between the positive ions in a giant metallic lattice and a ‘sea’ of delocalised ions

Explain in terms of structure and bonding that metals have good electrical conductivity

delocalised electrons can flow through the structure when a current is apllied

Explain in terms of structure and bonding that metals are malleable

layers of ion can slide over each other

Periodic table

an arrangement of elements in periods and groups and in order of increasing proton number/atomic number

Describe the change from metallic to non-metallic character across a period

Increase in nuclear charge and decrease in atomic size → tendency to gain electrons increases → non - metallic character increases

Explain similarities in the chemical properties of elements in the same group in terms of their electronic configuration

same number of valence electrons → similar chemical properties

Alkali metals

In group 1

Alkali metals’ decreasing melting and boiling point

delocalised electrons are further away from the nucleus → metallic bonds weaker

Alkali metals’ increasing density

mass increases when you move down the group

Alkali metals’ increasing reactivity with water

Outer electrons further away from the nucleus as you go down the group → valence electrons more easily lost/less tightly held together by positive nucleus

Similarities of group 1

- reactive metals

- soft

- low BP + MP

- reacts fast to air, will tarnish easily, losing shininess

- reacts with water to produce alkaline solutions of metal hydroxide and hydrogen gas

- increase reactivity

- mainly white compounds which dissolve in water

Lithium reaction with water

produce hydrogen gas

Sodium reaction with water

melts into a sphere that moves around the surface → effervescing (fizzing)

Potassiums reaction to water

metal melts into sphere → moves quickly on surface → lilac flame

Equation for reaction with oxygen

Element	Equation
Original	alkali metal + oxygen → alkali metal oxide
Lithium	2Li(s) + 2H2O(l) → 2LiOH + H2(g)
Sodium	2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)
Potassium	2K(s) + 2H2O(l) → 2KOH + H2(g)

Halogens

in group 7 → diatomic non - metals

Halogens’ increasing density

more electron shells when you move down → increase atomic mass and size

Halogens’ decreasing reactivity

atomic mass increases → increase in electron shells → atoms are larger → valence shell further away from nucleus → reduce ability to attract electrons

Halogens trends

- reactivity → decreases

- density → increases

- colour → gets darker

- BP + MP → increase → larger atoms, strong IMF between molecules

Appearance of chlorine at r.t.p (room temperature and pressure)

chlorine → a pale yellow-green gas

Appearance of bromine at r.t.p (room temperature and pressure)

bromine → a red-brown liquid

Appearance of iodine at r.t.p (room temperature and pressure)

iodine → a grey-black solid

Halide

Ion of respective halogen combined with a metal ion

Describe and explain the displacement reactions of halogens with other halide ions 

A more reactive halogen will displace a less reactive halide from its compound in solution

Equation of displacement

Element	Equation
Chlorine displacing potassium Bromide	Cl2​(aq)+2KBr(aq)→2KCl(aq)+Br2​(l)
Chlorine displacing potassium iodide	Cl2​(aq)+2KI(aq)→2KCl(aq)+I2​(s)
Bromine displacing potassium iodide	Br2​(aq)+2KI(aq)→2KBr(aq)+I2​(s)

Transition metals

- high densities → large atomic masses and closely packed atomic structures

- high melting points → delocalised electrons → stronger IMF between molecules

- low reactivity

- form coloured compounds

- often act as catalysts in elements and in compounds

Noble gases

group 8 → unreactive, monatomic gas → have complete valence shells → stable