1. 4.4.2 Physical Properties of Giant Metallic Elements

2. Sodium Sodium has the electron structure 1s 2 2s 2 2p 6 3s 1. When sodium atoms come together, the valence electron in the 3s orbital of one atom shares space with the corresponding electron on a neighboring atom to form a metallic bond Each sodium atom is touched by eight other sodium atoms. The 1 valence electron on each atom can move freely and becomes detached from its parent atom, resulting in a +1 positive charge. The electrons are said to be delocalized / mobile / free. The sodium atoms are held together by the strong electrostatic force of attraction between the positive sodium ions and the delocalized electrons.

3. Magnesium Why does Mg have a higher melting point than Na? e.g. Mpt (Na) = 98 o CMpt (Mg) = 650 o C Factors that cause this increase in the strength of the bond are: Mg has 2 electrons in its valence shell (1s 2 2s 2 2p 6 3s 2 ) Both of these electrons become delocalized, so the ‘sea’ has twice the number of electrons per atom than Na. The remaining +2 ‘ions’ have twice the charge and therefore there is a greater electrostatic attraction between the ‘ions’ and ‘sea’. Each Mg atom has 1 more proton in the nucleus compared to Na and therefore this extra proton results in a greater attraction for the delocalized electrons. Mg atoms have a smaller atomic radius than sodium atoms, and so the delocalized electrons are closer to the nuclei increasing the electrostatic attraction.

4. Physical Properties of Metals High Melting Points and Boiling Points Due to strong electrostatic attractions between the positive ions and delocalized valence electrons. Conduct Electricity The delocalized electrons are free to move enabling them to carry a current. Conduct heat Heat energy is conducted up by the delocalized electrons and transferred throughout the metal structure when they move. Hardness Metal are hard due to the strong electrostatic force of attraction between the ions and delocalized electrons.

5. Volatility Metals are not volatile. They do not turn into a vapor (gas) at low temperatures because the strong intramolecular electrostatic attractions between the positive ions and delocalized electrons are too strong to be broken. Malleability and ductility Metals are described as malleable (can be beaten into sheets) and ductile (can be pulled out into wires). If a small stress is applied the layers of atoms roll over each other without breaking the metallic bond.

6. Superconductors In a normal metal conductor the mobile electrons collide with the positive ions as they move through the metal releasing energy in the form of heat, heating up the metal (called resistance). The first superconductors were alloys of metals like nobidium, 41 Nb (at 0K) conduct electricity without releasing heat energy but they are not useful because they only do this at very low temperatures. In late 1980’s scientists discovered a new type of superconductor material that could operate at higher temperatures. Today, finding materials that can behave as superconductors at room temperatures is one of the great goals of chemists. Current research is focused on alloys of the element silicon.

7. Uses of Superconductors Superconductor are used to make very large electro magnets (coil of wire with a current moving through it) used in medicine (MRI), imaging equipment, maglev trains. In a maglev train large electromagnets made with superconductors provide the power for the train. The current created induces a current in the track causing the train to levitate or lift off the track, allowing it to travel much faster.