Bonding, Structure and Chemical Properties

1. Bonding, Structure and Chemical Properties CHEMISTRY 2 GCSE Additional Science Chapter 7

2. Non Metals Metals The Periodic Table GCSE Additional Science Chapter 7

3. Comparing the properties of metals and non-metals GCSE Additional Science Chapter 7

4. The key to understanding a metal’s properties lies in its structure Metals positive ions A metal structure is an ordered pattern of positive ions in a ‘sea’ of negative electrons. free electrons Ductility Electrons act as a type of lubricant between the layers of ions. This explains why it’s possible to pull metals to form wires. Electrical Conductors Connecting the sides to a battery makes the electrons move from the negative side towards the positive – this is the flow of current. Explaining the properties of METALS GCSE Additional Science Chapter 7 Melting Point The strength of metallic bonds depends on the number of outer electrons in the atoms (the more outer electrons there are , the higher the melting point).

5. Alloys Stainless steel is an example of an alloy used to make saucepans and cutlery. Some modern alloys can recover their shape after bending. These are used in frames for glasses. They are a type of ‘smart material’ called shape-memory alloy. Metallic Glass As mentioned previously, most solids have a structure that shows a regular pattern but it’s possible to form metals that show less of a pattern – these are the metallic glasses. GCSE Additional Science Chapter 7 Metallic glasses are three times as strong as steel and ten times more flexible, making them ideal for use as golf club-heads.

6. BONDINGIonic Structures Sodium chloride is formed when atoms of sodium bond with atoms of chlorine. Cl- Na+ GCSE Additional Science Sodium atom (Na) [2.8.1] Sodium ion (Na+) [2.8] Chapter 7 Chlorine atom (Cl) [2.8.7] Chloride ion (Cl-) [2.8.8] Both atoms are trying to achieve a full set of outer electrons. They can do this if the sodium atom gives its outer electron to the chlorine atom. We now have a sodium ion Na+, and a chloride ion Cl-.

7. Sodium ion (Na+) [2.8.] Chloride ion (Cl-) [2.8.8] BONDINGIonic Structures Na+ Cl- GCSE Additional Science Chapter 7 Sodium chloride (salt)

8. So there are two types of ion:- • Positive ion (cation) – the atom has lost an electron or electrons. • Negative ion (anion) – the atom has gained electron(s). • The ions attract and the attraction is ionic bonding. BONDINGIonic Structures The oppositely charged ions attract each other. They cluster around each other (six Cl-around each Na+ and vice versa) to make an ionic giant structure. Six Chloride ions cluster around one Sodium ion GCSE Additional Science Chapter 7 Six Sodium ions cluster around one Chloride ion Molecular structure of Sodium Chloride (Click molecule to show animation)

9. Properties of Ionic Compounds GCSE Additional Science Chapter 7

10. BONDINGCovalent Bonding Non-metal atoms bond with each other by sharing outer shell electrons. This is called COVALENT BONDING. Covalent bonding can produce: • Small molecules of elements, e.g. H2 • Small molecules of compounds, e.g. HCl GCSE Additional Science • Giant molecules of elements, e.g. diamond and graphite Chapter 7 • Giant molecules of compounds, e.g. SiO2

11. BONDINGCovalent molecules Some elements form covalent compounds. This happens as atoms share electrons. H Cl GCSE Additional Science Chlorine atom (Cl) [2.8.7] Hydrogen atom (H) [1] Molecule of hydrogen chloride (HCl) Chapter 7 Hydrogen has the electron pattern of helium, and chlorine has the electron pattern of argon. This is written as H-Cl, where the ‘-’ represents a covalent bond (pair of shared electrons).

12. Properties of molecular covalent compounds GCSE Additional Science Chapter 7

13. Ca2+ F- H H 2 Mg2+ Cl- O 2 Cl O H H Cl H N H H Show the answers An exercise to recognise atomic or covalent bonds.(Only the outer shell is shown in the diagrams) ionic covalent covalent covalent ionic GCSE Additional Science Chapter 7 Cu Cu2+ O2- covalent ionic

14. Comparing the properties of graphite and diamond Giant Covalent Structures Some covalent molecules exist as giant covalent structures. These have a high melting point because all the atoms are held by strong covalent bonds. Graphite and diamond are examples of giant covalent structures made up of a collection of carbon atoms only. Diamond Graphite GCSE Additional Science Chapter 7

15. An explanation of the properties of diamond and graphite Diamond Graphite Graphite has layers formed from hexagonal rings – these layers can slide over each other, and this is why it is used as a lubricant. Every atom is bonded to 4 other atoms. Every outer electron has its role to play in the covalent bonding that happens here. The result is a very rigid structure. As there are no free electrons, it doesn’t conduct electricity and it’s a good conductor of heat. GCSE Additional Science Chapter 7 Every carbon atom bonds strongly to other carbon atoms by three covalent bonds. The fourth outer electron in each atom is free to move, and this is what makes graphite a good conductor.

16. Fullerene C60 Carbon Nanotube The future, and other forms of carbon Whilst experimenting with Fullerene C60, it was found that other structures of carbon could be formed. One of them is seen below: The carbon atoms are bonded covalently into a football shape. • The nanotube is like rolled graphite. • It conducts electricity • It’s very small – 10,000 times thinner than a human hair • Crystals can be grown inside it • They may solve the problem of how to produce smaller circuits, where they might replace wires. GCSE Additional Science Chapter 7 Nanotube Human hair