(a) Group 1 (alkali metals) – lithium, sodium and potassium

2:01 understand how the similarities in the reactions of lithium, sodium and potassium with water provide evidence for their recognition as a family of elements

Group 1 metals, such as potassium, sodium and lithium, react with water to produce a metal hydroxide and hydrogen. For example:

          lithium   +   water   →   lithium hydroxide   +   hydrogen

          2Li (s)   +   2H₂O (l)   →   2LiOH (aq)   +   H₂ (g)

The observations for this reaction of lithium and water are:

  1. Fizzing
  2. Lithium floats and moves around on the water
  3. Lithium disappears

The reactions of sodium or potassium and water are somewhat similar, giving those observations and producing a metal hydroxide and water.

This similarity in reactions provides evidence that the 3 metals are in the same family of elements (group of the Periodic Table).

2:02 understand how the differences between the reactions of lithium, sodium and potassium with air and water provide evidence for the trend in reactivity in Group 1

Lithium is the first element in group 1 of the Periodic Table. The observations for the reaction of lithium and water are:

  1. fizzing (hydrogen gas is released)
  2. Lithium floats and moves around on the water
  3. Lithium disappears

The reactions of sodium or potassium and water are similar but more vigorous:

  • When sodium reacts with water, the sodium also melts.
  • When potassium reacts with water, the potassium also catches fire with a lilac flame.

When the group 1 metals react with air they show a similar trend in reactivity as we go down the group of the Periodic Table.

Therefore, as we go down group 1 (increasing atomic number), the elements become more reactive: Li<Na<K<Rb<Cs<Fr

2:03 use knowledge of trends in Group 1 to predict the properties of other alkali metals

From the data in the table, it is possible to deduce the properties of francium from the trends in the other group 1 metals.

For example, we can predict that francium will have a melting point around 20⁰C and a density of just over 2g/cm³.

We can also predict that francium will react violently with water, producing francium hydroxide and hydrogen.

Alkali metalMelting point (⁰C)Density (g/cm³)Reaction with waterProducts
lithium (Li)1810.53fizzinglithium hydroxide + hydrogen
sodium (Na)980.97rapid fizzingsodium hydroxide + hydrogen
potassium (K)630.86vigorous fizzing and lilac flamepotassium hydroxide + hydrogen
rubidium (Rb)391.53?rubidium hydroxide + hydrogen
caesium(Cs)291.88?caesium hydroxide + hydrogen
francium (Fr)????
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Section 1: Principles of chemistry

      a) States of matter

      b) Atoms

      c) Atomic structure

     d) Relative formula masses and molar volumes of gases

     e) Chemical formulae and chemical equations

     f) Ionic compounds

     g) Covalent substances

     h) Metallic crystals

     i) Electrolysis

 Section 2: Chemistry of the elements

     a) The Periodic Table

     b) Group 1 elements: lithium, sodium and potassium

     c) Group 7 elements: chlorine, bromine and iodine

     d) Oxygen and oxides

     e) Hydrogen and water

     f) Reactivity series

     g) Tests for ions and gases

Section 3: Organic chemistry

     a) Introduction

     b) Alkanes

     c) Alkenes

     d) Ethanol

Section 4: Physical chemistry

     a) Acids, alkalis and salts

     b) Energetics

     c) Rates of reaction

     d) Equilibria

Section 5: Chemistry in industry

     a) Extraction and uses of metals

     b) Crude oil

     c) Synthetic polymers

     d) The industrial manufacture of chemicals