### Atomic Structure and Bonding Question 1

1. The mass number of potassium is 39 and its proton number is 19.

i. State the number of electrons in the potassium atom. [1]

ii. Determine the number of neutrons in the potassium atom. [1]

2. Potassium reacts with chlorine by donating electrons.

i. State the number of electrons donated by potassium and the charge on the potassium ion. [2]

ii. Write the formula of potassium fluoride. [1]

iii. State one physical property of potassium fluoride. [1]

3. Describe how magnesium oxide can be prepared. [2]
4. Explain why magnesium oxide does not react with copper.[2]

### Solution

1. i. 19

because number of protons = number of electrons in a neutral atom.

ii. Number of neutrons = mass number – proton number

= 39 – 19

= 20

2. i. Number of donated electrons = 1

charge on the potassium ion = +1

Potassium has 19 electrons, which means that its electronic configuration is 2.8.8.1. It donates 1 electron because metals donate the electrons in the outer shell only, which is 1 electron in this case.

When an atom loses a electrons it becomes an positively charge ion whose magnitude is equal to the number of electrons lost. Since a potassium atom loses 1 electron, the charge on its ion is +1.

ii. KF

The symbol of potassium is K and the symbol of fluorine is F. One potassium atom donates one electron to one fluorine atom, which means they combine in the ratio 1:1, hence the formula KF.

iii. Solid at room temperature.

Potassium fluoride is a chemical combination of a metal (potassium ) and a non metal (fluorine) and is therefore an ionic compound. Properties of potassium fluoride are basically the properties of ionic compounds.

3. By heating a magnesium ribbon is air.

Reactive metals react with the oxygen in the air when heated in air. The resultant is an oxide of the metal.

4. Copper is less reactive than magnesium, so it cannot displace magnesium from its compound.

#### Sydney Chako

Mathematics, Chemistry and Physics teacher at Sytech Learning Academy. From Junior Secondary School to Tertiary Level Engineering Mathematics and Engineering Science.