Families of Elements and Predictions: Quick Revision

A brief note on Families of Elements and Predictions. Read it before a test. Try each question at the end before you open its answer.

Four families

Key reactions

• Alkali metal and water: $2\text{M} + 2\text{H}_2\text{O} \rightarrow 2\text{MOH} + \text{H}_2$.
• A more reactive halogen displaces a less reactive one: $\text{Cl}_2 + 2\text{KBr} \rightarrow 2\text{KCl} + \text{Br}_2$.

Predicting

The place gives the valency, the formulas, the reactivity and the nature. A property in the middle of a group can be estimated as the average of its two neighbours.

A worked example

Caesium lies near the bottom of group 1. Predict four things about it.

1. Valency. One outer electron: valency $1$.
2. Oxide and chloride. $\text{Cs}_2\text{O}$ and CsCl.
3. With water. Even more violent than potassium, because its outer electron is far from the nucleus.
4. Oxide. Strongly basic, like every alkali metal oxide.

Practice with new numbers

A program to try

The program shows which halogen displaces which.

Mistakes to avoid

• Thinking reactivity rises down every group. It rises for metals but falls for the halogens.
• Expecting a less reactive halogen to displace a more reactive one. Iodine cannot free chlorine.
• Calling noble gases molecules. They are single atoms.
• Treating an estimate from neighbours as exact. The steps are not perfectly even.

Check yourself

1. Which gas forms when lithium reacts with water?

2. Will bromine water react with sodium chloride solution?

3. Why is neon used in glowing signs and not oxygen?

4. Predict the formula of radium chloride. Radium is in group 2.