Chemical properties of the alkali metals
The smallest part of an element that can exist. of the The first vertical column of elements in the periodic table, starting with lithium and ending with francium. Also called the alkali metals.A substance made of one type of atom only. all have one Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons. in their outer shell. This means that the A base which is soluble in water. metals all have similar chemical The characteristics of something. In chemistry, chemical properties include the reactions a substance can take part in. Physical properties include colour and boiling point..
Reactions with water
The alkali metals react with water to produce a metal hydroxide and hydrogen. For example, sodium reacts with water:
sodium + water → sodium hydroxide + hydrogen
2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)
Sodium hydroxide is an alkali. It is a A substance that reacts with an acid to neutralise it and produce a salt. that When a substance breaks up and mixes completely with a solvent to produce a solution. in water to form an Having a pH greater than 7.Mixture formed by a solute and a solvent.. This solution:
- has a Scale of acidity or alkalinity. A pH (power of hydrogen) value below 7 is acidic, a pH value above 7 is alkaline. greater than 7
- turns A chemical solution that produces many different colour changes corresponding to different pH levels. solution blue or purple
Question
Write the word equation and balanced equation for the reaction of potassium with water.
potassium + water → potassium hydroxide + hydrogen
2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)
Reactions compared
The table shows the main observations when lithium, sodium and potassium are added to water. The A measure of how vigorously a substance will react. The more reactive it is, the greater its reactivity and the more vigorous its reactions will be. of these metals increases going down the group. With very reactive metals such as potassium, enough energy is transferred by heating to ignite the hydrogen gas.
| Group 1 element | Observations |
| Lithium, Li | Fizzes steadily, slowly becomes smaller until it has all reacted |
| Sodium, Na | Melts to form a ball, fizzes rapidly, quickly becomes smaller until it disappears |
| Potassium, K | Quickly melts to form a ball, burns violently with sparks and a lilac flame, reacts rapidly, often with a small explosion |
| Group 1 element | Lithium, Li |
|---|---|
| Observations | Fizzes steadily, slowly becomes smaller until it has all reacted |
| Group 1 element | Sodium, Na |
|---|---|
| Observations | Melts to form a ball, fizzes rapidly, quickly becomes smaller until it disappears |
| Group 1 element | Potassium, K |
|---|---|
| Observations | Quickly melts to form a ball, burns violently with sparks and a lilac flame, reacts rapidly, often with a small explosion |
Example
Rubidium is placed below potassium in group 1. Predict what is seen when rubidium is added to water.
Rubidium should melt very quickly. It should burn very violently and disappear almost instantly with an explosion.
Explaining the trend
When an element in group 1 takes part in a reaction, its atoms lose their outer electrons and form positively charged Electrically charged particle, formed when an atom or molecule gains or loses electrons., called An atom or group of atoms that have lost electrons and become positively charged. Most cations are formed from metals.. The more easily these cations form, the more The tendency of a substance to undergo a chemical reaction.the metal.
The reactivity of group 1 elements increases as you go down the group because:
- the atoms become larger
- the outer electron becomes further from the The central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. The plural of nucleus is nuclei.
- the force of attraction between the nucleus and the outer electron decreases
- the outer electron is lost more easily
