Group 1: Alkali Metals
Alkali metals are found in Group 1 of the periodic table, and show a trend in chemical and physical properties. Alkali metals are soft and have relatively low melting points.
Alkali metals react vigorously with water to produce a hydroxide and hydrogen gas. The reactions become more violent down the group, with lithium fizzing and moving across the surface, sodium moving with greater speed and bubbling, and potassium producing enough heat to ignite the hydrogen gas produced.
As the atomic number increases down the group, the atom gets bigger due to the increased number of shells. The electrostatic force of attraction between the positively charged nucleus and the negatively charged electron in the outermost shell decreases as they become further apart. Therefore, less energy is required to overcome this force of attraction and the reactions become more vigorous.
Group 7: Halogens
| Element | Colour | Physical State at rtp |
| Chlorine | Green | Poisonous green gas which bleaches damp litmus paper |
| Bromine | Red-Brown | Poisonous liquid which gives off orange vapour |
| Iodine | Dark Grey | Crystalline solid which gives off purple vapour when heated |
| Exist as diatomic molecules with two atoms held together by a covalent bond. Non-metallic and are poor conductors with increasing melting and boiling points and density down the group | ||
Halogens react with metals to form salts which contain halide ions. The Halogens form hydrogen halides when dissolved in water to form acidic solutions such as hydrochloric acid.
Down the group, reactivity decreases. This can be seen in displacement reactions. A more reactive halogen like chlorine will displace a less reactive halogen like iodine in an ionic compound. Displacement reactions are an example of redox reactions as the less reactive halogen loses electrons while the more reactive halogen gains electrons at once, meaning the more reactive halogen becomes part of the ionic compound.
As the atomic number increases down the group, the atom gets bigger due to the increased number of shells. The electrostatic force of attraction between the positively charged nucleus and the negatively charged electron in the outermost shell decreases as they become further apart. Ions do not form as easily so reactivity decreases as energy is used to make the ion.
Group 0: Noble Gases
The Noble Gases are chemically inert because their outermost electron shells are full – they have a stable electronic configuration. Therefore, they are very unlikely to form ions. Boiling and melting points and density increases down the group.
- Krypton is used in photography lighting as it produces a very bright white light
- Argon is denser than air so is put in wine barrels to stop oxygen from reacting with wine
- Helium has a very low density and is non-flammable so is used in balloons
- Neon produces a red light when electricity passes through it, so it is used in illuminated signs