10th grade atoms, elements and the periodic table

Example

What type of bonding is in potassium bromide (KBr)?

1. Ionic bonds form between metals and non-metals when electrons are transferred.
2. So the answer is: ionic

Answer: ionic

Example

Calculate the relative formula mass (Mr) of CO₂. Relative atomic masses: C = 12, O = 16.

1. 1 × 12 + 2 × 16 = 44
2. So the answer is: 44

Answer: 44

Example

Natural boron contains 20 % of mass 10 and 80 % of mass 11. Calculate its relative atomic mass to 1 decimal place.

1. 10 × 20 + 11 × 80 = 1080
2. 1080 ÷ 100 = 10.8
3. So the answer is: 10.8

Answer: 10.8

Example

Which type of radiation: a fast-moving electron from the nucleus?

1. Beta particles are fast electrons from the nucleus: stopped by a few mm of aluminium.
2. So the answer is: beta (β)

Answer: beta (β)

Example

A sample has an activity of 1600 Bq. Its half-life is 6 days. What is its activity after 24 days, in Bq?

1. 24 ÷ 6 = 4
2. 1600 ÷ 2^4 = 100
3. So the answer is: 100 Bq

Answer: 100 Bq