The Physical and Chemical Properties of the Group 1 elements Lithium Atomic Number 3 Mass Number 7 Sodium Atomic Number 11 Mass Number 23 Potassium Atomic Number 19 Mass Number 39 Rubidium Atomic Number 37 Mass Number 86 Caesium Atomic Number 55 Mass Number 133 What is the number of protons, electrons and neutrons for each element? What is the electronic configuration for the first three elements? Why are the elements all in group 1?

ANSWERS Element Lithium 3 4 2,1 Sodium 11 12 2,8,1 Potassium 19 20 protons neutrons electrons arrangement Lithium 3 4 2,1 Sodium 11 12 2,8,1 Potassium 19 20 2,8,8,1 Rubidium 37 49 2,8,18,8,1 Caesium 55 78 2,8,18,18,8,1 ALL HAVE 1 electron in outer shell

Physical Properties Melting Points Density Hardness

Melting Points I Lithium 180oC Sodium 98oC Potassium 630C Rubidium 39oC Caesium 29oC What is surprising about the melting points of these elements? ( Melting Points of Al 6600C, Fe 1540oC, Cu 1084oC) What does this tell you about the bond between the atoms in each of the group 1 elements? What is the trend in melting point?

Melting points II All have Low melting points. Metals usually have HIGH melting points They must have weak forces of attractions (bonds) between the atoms. (METALLIC BOND IS WEAK IN GROUP ONE METALS) Melting points decreases down group

Densities I Lithium 0.5 g/cm3 Sodium 0.97 g/cm3 Potassium 0.86 g/cm3 Rubidium 1.5 g/cm3 Caesium 1.9 g/cm3 What is surprising about the densities of these elements? ( Densities of Al 2.7g/cm3, Fe 7.9g/cm3, Cu 8.9g/cm3) What is the trend in density?

Densities II All have Low densities. Metals usually have HIGH densities The atoms must be Loosely packed together Density increases down group. .

HARDNESS II All are soft and can be cut with a knife Metals are usually hard. Hardness decreases down group. It becomes easier to cut them up https://thorntoncollege.fireflycloud.net/Resources/Subjects%20%5BF4%5D/Science%20%5BF5%5D/Chemistry%20%5BF6r%5D/KS4%20Chemistry%20%5BF9j%5D/Revision%20Sheets%20%5BF9l%5D/group%201.mp4

Chemical Properties Corrosion – oxidation in air Reaction with pure Oxygen Reaction with water See video on Firefly Group 1 elements https://thorntoncollege.fireflycloud.net/Resources/Subjects%20%5BF4%5D/Science%20%5BF5%5D/Chemistry%20%5BF6r%5D/KS4%20Chemistry%20%5BF9j%5D/Revision%20Sheets%20%5BF9l%5D/group%201.mp4

Reaction with Water II As before, Reactivity increases down the group as illustrated by Metal moves much faster After Na, the Hydrogen catches fire so more energy must be given off After K, Explosions occur Alkali containing Sodium = Sodium Hydroxide Formula of Sodium Hydroxide = NaOH.

Reaction with Water III SODIUM AND WATER  SODIUM HYDROXIDE AND HYDROGEN 2Na + 2H2O  2NaOH + H2 Equations for other metals 2M + 2H2O  2MOH + H2 (Swap symbol of metal with the M above)

Reasons for reactivity NB Full outer shell = stable atom NB In reactions atoms lose/gain or share electrons to achieve full outer shell NB Group 1 elements have 1 electron in their outer shell SO to achieve full outer shell they: LOSE ONE ELECTRON during reactions.

Reasons for reactivity Further the electron in outer shell is from the nucleus the easier it is to lose. Inner shells SHIELD (dilute) effect of nucleus. (Think about putting sheets of paper between two magnets, force decreases)

Uses of Sodium and Compounds