Chemistry Topic 6 - Groups in the Periodic table

Group 1: Alkali Metals

Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Caesium (Cs), Francium (Fr)

1 similar chemical property of Group 1

1 electron in their outer shell, and form 1+ ions

What differs between alkalis and other metals?

alkalis are soft and have relatively low mp and bp

What changes happen as you go down Group 1?

The melting point decreases and the reactivity increases.

Explain the increase in reactivity as you go down the group 1

As you go down the group the number of energy shells increases.
Thus, the distance between the negatively charged outer shell of electrons and the positively charged nucleus increases, which means the attractive electrostatic forces between them weaken.
Therefore, there is an increase in reactivity as you go down the group due to it being gradually easier to lose the remaining outer electron.

Explain the decrease in melting point as you go down the group 1.

As you go down the group the number of energy shells increases.
In a metal, there are attractive electrostatic forces between the positive nuclei and the sea of delocalised electrons
An increase in energy shells means that the forces stretch over a larger distance as you go down the group and they become weaker.
Thus, less and less energy is needed to break those forces as you go down the group

Alkali reaction with air

corrodes quickly

Lithium reaction with water

Fizzes steadily, gradually disappears

alkali reactions with water

fizzes and gives off hydrogen asymmetrically

Sodium reaction with water

Fizzes rapidly, melts into a ball and disappears quickly

Potassium reaction with water

Ignites with sparks, hydrogen burns and a lilac flame, disappears very quickly

Group 7 Halogens

Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), Astatine (At)

All halogens are… (think atomically)

diatomic

fluorine colour and state and room temperature

Pale yellow gas

chlorine colour and state and room temperature

Pale green gas

bromine colour and state and room temperature

dark-red liquid, red/brown vapour

iodine colour and state and room temperature

Dark grey solid with purple vapour

hazard of halogens

all of them have very toxic/poisonous vapours and must be handled in a fume cupboard

Similar chemical properties of halogens

form 1- anions

What changes happen as you go down Group 7?

decrease in reactivity, increase in mp and bp

Explain the increase in melting point as you go down the group 7.

As you go down the group the number of energy shells increases.
Thus, the molecule gets bigger as you go down the group which leads to stronger intermolecular forces

Explain the decrease in reactivity as you go down the group 7

As you go down the group the number of energy shells increases.
Thus, the distance between the negatively charged outer shell of electrons and the positively charged nucleus increases, which means the attractive electrostatic forces between them weaken.
Therefore, there is a decrease in reactivity as you go down the group due to it being gradually harder to gain the incoming electron

Test for chlorine

damp blue litmus paper turns white in chlorine gas

Test for hydrogen

Squeaky pop with lighted splint in a test tube

Displacement reactions of halogens

A more reactive halogen can displace a less reactive halogen from its salt

2KBr + Cl2 →

2KCl + Br2(yellow)

2KI + Cl₂→

2KCl + I₂ (brown)

2KI + Br₂→

2KBr + I₂ (brown)

colour of chlorine water

colourless

colour of bromine water

yellow

colour of iodine water

brown

OILRIG stands for

Oxidation is loss of electrons
Reduction is gain of electrons

redox reaction

A reaction in which 1 element is reduced and one is oxidised.

how to solve a redox reaction

1.separate the compounds into its ionic individuals(KCl goes to K+ + Cl-)
2.cancel out spectator ions - these are the symbols that are the same on each side
3.form 2 ionic equations from the 2 substances left. Make sure that the net electron gain and loss is 0.(2I- - 2e- = I2 Br2 + 2e- = 2Br- )
4.Deduce which element has been reduced and oxidised from OIL RIG

spectator ion

an ion that appears on both sides of an equation and is not directly involved in the reaction

Group 0 - Noble Gases

Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), Radon (Rn)

Group 0 - Noble Gases properties

colourless
v low mp/bp
poor conductors of heat + electricity
all chemically inert and stable as they have a full outer shell of electrons, which means that there is no need to ionically/covalently bond

Why are noble gases hard to discover?

They are all chemically inert so very hard to notice any chemical activity from them

Uses of krypton

used in photography as a brilliant white light is produced when electricity passed through it

Uses of argon

Used in lightbulbs
added in crisp packets and the space above the wine in wine barrels to stop oxygen reacting with them(argon denser than air)

Uses of helium

balloons and airships as it has a v low density and is non-flammable