Group 1 Metals with Water
The Group 1 metals
- The Group 1 metals are called the alkali metals because they form alkaline solutions with high pH values when reacted with water
- Group 1 metals are lithium, sodium, potassium, rubidium, caesium and francium
- They all end in the electron configuration ns1
Physical properties of the Group 1 metals
- The Group 1 metals:
- Are soft and easy to cut, getting softer and denser as you move down the group
- Have shiny silvery surfaces when freshly cut
- Conduct heat and electricity
- They all have low melting points and low densities and the melting point decreases going down the group as the atomic radius increases and the metallic bonding gets weaker
Group 1 metals in The Periodic Table
The alkali metals are located on the left of the periodic table in the first column of the s block
Chemical properties of the Group 1 metals
- They react readily with oxygen and water vapour in air so they are usually kept under oil to stop them from reacting
- Group 1 metals will react similarly with water, reacting vigorously to produce an alkaline metal hydroxide solution and hydrogen gas
Table of the reactions of Group 1 metals and water
| Element | Reaction |
| Lithium |
2Li (s) + 2H2O (l) → 2LiOH (aq) + H2 (g) Lithium floats and reacts slowly H2 gas released, lithium keeps shape |
| Sodium |
2Na (s) + 2H2O (l) → 2NaOH (aq) + H2 (g) Sodium reacts with a vigorous release of H2 gas Heat produced sufficient to melt the unreacted metal, which forms a small ball that moves around on the water surface NaOH formed which produces a highly alkaline solution |
| Potassium |
2K (s) + 2H2O (l) → 2KOH (aq) + H2 (g) Reacts more violently than sodium, bubbles of H2 gas, melts into a shiny ball that dashes around on the surface Hot enough to ignite H2 gas, potassium burns with a lilac flame |
Worked example
What would you see when sodium is added to water?
I. A gas is given off
II. The temperature of the water increases
III. A clear, colourless solution is formed
A. I and II only
B. I and III only
C. II and III only
D. I, II and III
Answer
- The correct option is D
-
- Bubbles of hydrogen gas are given off
- The sodium melts, so that tells you it is an exothermic reaction
- The product, sodium hydroxide, is very soluble so a clear, colourless solution would be formed
Alkali metals with halogens
- All the alkali metals react vigorously with the halogens in Group 17
- The reaction results in an alkali metal halide salt
2Na (s) + Cl2 (g) → 2NaCl (s)
- The reaction becomes increasingly vigorous going down Group 1 because:
- The atoms of each element get larger going down the group
- This means that the ns1 electron gets further away from the nucleus and is shielded by more electron shells.
- The further an electron is from the positive nucleus, the easier it can be lost in reactions
Worked example
Which pair of elements has the most vigorous reaction?
A. Cs and I
B. Li and Cl
C. Cs and F
D. Li and F
Answer
- The correct option is C.
-
- You need to choose the lowest element in Group 1 and the highest element in Group 17 to predict the most vigorous reaction
- This is because reactivity increases going down Group 1, but decreases going down Group 17