CHEMISTRY Unit 1.5/1.6 (AQA - The periodic table and group trends)

Typical radius of an atom in standard form and nanometres

About $0.1\,\text{nm}$ (or $1 \times 10^{-10}\,\text{m}$)

Radius of a nucleus compared to the overall atom

Less than $\frac{1}{10\,000}$ of the radius of the atom (about $1 \times 10^{-14}\,\text{m}$)

Location of almost all the mass of an atom

The nucleus

Mass number

The total sum of protons and neutrons in an atom

Isotopes

Atoms of the same element that have the same number of protons but different numbers of neutrons

Calculation for the number of neutrons in an atom

$$\text{Number of neutrons} = \text{mass number} - \text{atomic number}$$

What are the group 1 elements known as?

The alkali metals

How many electrons do group 1 elements have in their outer shell?

1 electron

How does reactivity change as you go down group 1? Why?

Reactivity increases down the group. The outer electron is further from the nucleus, so there is less electrostatic attraction and it is lost more easily.

What are the physical properties of group 1 metals?

Soft, low density, low melting and boiling points

What happens when a group 1 metal reacts with water?

It produces a metal hydroxide and hydrogen gas

Sodium reaction with water (word equation)

Sodium + water → sodium hydroxide + hydrogen

What are the group 7 elements known as?

The halogens

How many electrons do group 7 elements have in their shell?

7 electrons

How does reactivity change as you go down group 7? Why?

Reactivity decreases down the group. It becomes harder to attract an extra electron because the outer shell is further from the nucleus with more shielding.

States and colours of:

Chlorine

Bromine

Iodine

At room temperature

Chlorine - greenish-yellow gas

Bromine - red-brown liquid

Iodine - dark grey solid

What is a displacement reaction in group 7?

A more reactive halogen will displacement a less reactive halogen from an aqueous solution of its salt

How do melting and boiling points change down group 7 and 0?

They increase down the group because the molecules become larger

What are the group 0 elements known as?

The noble gases

Why are group 0 elements unreactive?

They have a full outer shell of electrons

What state are noble gases at room temperature?

They are all colourless gases

Do noble gases exist as single atoms or molecules?

Monatomic gases (single atoms, not bonded to each other)

What is the trend in density as you go down group 0?

Density increases down the group