Group 1
The first vertical column of elements in the periodic table, starting with lithium and ending with francium. Also called the alkali metals. contains A substance made of one type of atom only. placed in a vertical column on the far left of the A tabular representation of all known elements in order based on atomic number, eg all the noble gases are found on the right of the periodic table.. The elements in group 1 are called the The first vertical column of elements in the periodic table, starting with lithium and ending with francium. Also called group 1..
The alkali metals share similar A description of the appearance of a substance or how it acts without involving chemical reactions. For example, state, melting point, conductivity, etc.. For example, they:
- are soft (they can be cut with a knife)
- have relatively low The temperature at which a solid changes into a liquid as it is heated.
- have low densities
Question
The table shows the melting points of five alkali metals. Use this information to describe how melting point changes in group 1.
| Element | Melting point (°C) |
| Lithium, Li | 180 |
| Sodium, Na | 98 |
| Potassium, K | 63 |
| Rubidium, Rb | 39 |
| Caesium, Cs | 28 |
| Element | Lithium, Li |
|---|---|
| Melting point (°C) | 180 |
| Element | Sodium, Na |
|---|---|
| Melting point (°C) | 98 |
| Element | Potassium, K |
|---|---|
| Melting point (°C) | 63 |
| Element | Rubidium, Rb |
|---|---|
| Melting point (°C) | 39 |
| Element | Caesium, Cs |
|---|---|
| Melting point (°C) | 28 |
Going down group 1, the melting point decreases.
Chemical properties of group 1 elements
The smallest part of an element that can exist. of group 1 elements 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 alkali metals all have similar A description of how a substance reacts with other substances. For example, flammability, pH, reaction with acid, etc..
When a group 1 element takes part in a reaction, its atoms each lose one electron. This forms positively charged Electrically charged particle, formed when an atom or molecule gains or loses electrons.. The ions have a stable arrangement of electrons, with a complete outer shell.
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 A base which is soluble in water.. 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
Complete the word equation and balanced symbol equation for the reaction of potassium with water.
potassium + water → ______________ + ______________
2 ___(s) + 2H2O(l) → ___KOH(aq) + ______(g)
potassium + water → potassium hydroxide + hydrogen
2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)
Reactions compared
The table shows 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.
| Element | Observation when added to water |
| Lithium, Li | Fizzes steadily; slowly becomes smaller until it disappears |
| Sodium, Na | Fizzes rapidly; melts to form a ball; quickly becomes smaller until it disappears |
| Potassium, K | Burns violently with sparks and a lilac flame; quickly melts to form a ball; disappears rapidly, often with a small explosion |
| Element | Lithium, Li |
|---|---|
| Observation when added to water | Fizzes steadily; slowly becomes smaller until it disappears |
| Element | Sodium, Na |
|---|---|
| Observation when added to water | Fizzes rapidly; melts to form a ball; quickly becomes smaller until it disappears |
| Element | Potassium, K |
|---|---|
| Observation when added to water | Burns violently with sparks and a lilac flame; quickly melts to form a ball; disappears rapidly, often with a small explosion |
Question
Rubidium is placed below potassium in group 1. Predict what is seen when rubidium is added to water.
Rubidium melts very quickly. It burns violently and explodes.
Reactions with oxygen
The group 1 elements react with oxygen from the air to make metal Compound containing oxygen or oxide ions..
At room temperature, oxygen reacts with the surface of the metal. This forms a white oxide, which covers the surface. The metal below the surface does not react.
The alkali metals burn vigorously when heated and placed in a gas jar of oxygen. The oxide forms as white smoke.
For example:
sodium + oxygen → sodium oxide
4Na(s) + O2(g) → 2Na2O(s)
The reactivity of the group 1 elements increases down the group, so their reactions with oxygen get more vigorous.
Question
Predict which becomes white more quickly on exposure to air - a piece of rubidium, or a piece of lithium. Explain your answer.
The rubidium becomes white more quickly. This is because rubidium is below lithium in group 1, so rubidium is more The tendency of a substance to undergo a chemical reaction. and so it reacts with the oxygen in the air to form an oxide layer more quickly.
Reactions with chlorine
The group 1 elements react vigorously with chlorine. The products of the reactions are chlorides. At room temperature the chlorides are white solids. They dissolve in water to form colourless solutions. For example:
sodium + chlorine → sodium chloride
2Na(s) + Cl2(g) → 2NaCl(s)
The reactions with chlorine get more vigorous going down the group.
Question
Balance the equation for the reaction of potassium with chlorine.
_____K(s) + Cl2(g) → _____KCl(s)
2K(s) + Cl2(g) → 2KCl(s)
Explaining the trend in reactivity
When a group 1 element takes part in a reaction, each of its atoms loses its outer electron to form a positively charged ion. The more easily the ions form, the more reactive the metal.
Going down group 1:
- 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