Group 1 Notes

Edexcel GCSE Chemistry: Revision notes

Key facts

  • Group 1 elements are the alkali metals. They are soft with low melting points.
  • Alkali metal + water gives a metal hydroxide and hydrogen.
  • Reactivity increases down the group: lithium < sodium < potassium.
  • Each atom has one outer electron, which it loses to form a 1+ ion.
  • Going down, the outer electron is further from the nucleus and more shielded, so it is easier to lose.

Physical properties

The alkali metals are soft, low-melting-point metals, and their melting points fall going down the group.

Lithium, sodium, potassium, rubidium, caesium and francium are the alkali metals. Their position in the leftmost column decides their chemistry.

They are soft enough to cut with a knife. They have low melting points compared with most metals, and the melting point decreases down the group.

050100150LiNaKRbCsElementMelting point (°C)
Melting points fall going down Group 1.
123456701234561H2He3Li4Be5B6C7N8O9F10Ne11Na12Mg13Al14Si15P16S17Cl18Ar19K20Ca21Sc22Ti23V24Cr25Mn26Fe27Co28Ni29Cu30Zn31Ga32Ge33As34Se35Br36Kr37Rb38Sr39Y40Zr41Nb42Mo43Tc44Ru45Rh46Pd47Ag48Cd49In50Sn51Sb52Te53I54Xe55Cs56Ba
Group 1 is the first column.

What happens to the melting point of the alkali metals going down Group 1?

Reaction with water

Lithium, sodium and potassium react with water to make a metal hydroxide and hydrogen, more violently down the group.

alkali metal + water → metal hydroxide + hydrogen

2 Na+2 HX2O→2 NaOH+HX2\ce{2Na + 2H2O -> 2NaOH + H2}

All three float, move around and fizz as hydrogen is given off. Sodium melts into a ball. Potassium reacts violently and its hydrogen ignites with a lilac flame. The solution formed is an alkali.

  1. 1

    Lithium

    floats and fizzes steadily

  2. 2

    Sodium

    melts into a ball and darts about

  3. 3

    Potassium

    hydrogen ignites with a lilac flame

Reactivity with water increases down Group 1.

Lithium

Floats and fizzes:
Yes
Melts into a ball:
No
Hydrogen ignites (lilac flame):
No

Sodium

Floats and fizzes:
Yes
Melts into a ball:
Yes
Hydrogen ignites (lilac flame):
No

Potassium

Floats and fizzes:
Yes
Melts into a ball:
Yes
Hydrogen ignites (lilac flame):
Yes

Name the two products when sodium reacts with water.

The reactivity pattern

Reactivity increases down Group 1, so rubidium and caesium react even more violently than potassium.

Reactivity increases going down: lithium < sodium < potassium.

This pattern lets you predict that rubidium and caesium would react more violently with water than potassium does.

  1. 1

    Lithium

    fizzes steadily

  2. 2

    Sodium

    fizzes vigorously and melts into a ball

  3. 3

    Potassium

    violent, hydrogen ignites with a lilac flame

  4. 4

    Rubidium and caesium

    predicted to be even more violent

Reaction with water gets more vigorous down the group

Which is more reactive with water, sodium or potassium?

Why reactivity increases

Lower down the group the outer electron is further from the nucleus and more shielded, so it is lost more easily.

Every Group 1 atom has one outer electron, lost to form a 1+ ion.

Going down the group:

  • atoms have more shells, so the outer electron is further from the nucleus
  • it is more shielded from the nucleus by the inner shells
  • so it is easier to lose, and reactivity increases
Li3p 4n

Lithium

2,1

Na11p 12n

Sodium

2,8,1

K19p 20n

Potassium

2,8,8,1

One outer electron each, one more shell for each step down.

Why is potassium more reactive than lithium?

Try an exam question

Explain why potassium is more reactive than lithium.

[3 marks]

That's the notes covered.

Carry on to the next subtopic.