Bonding Structure and Chemical Properties WJEC Chemistry Unit

Bonding, Structure and Chemical Properties WJEC Chemistry Unit 2 - 2. 1 (part) WJEC Double Award Unit 5 - 5. 1 (part)

Periodic Table of Elements Non-metals Metals

Comparing the properties of metals and nonmetals Metals Non-Metals Good conductors of electricity Poor conductors of electricity Good heat conductors Poor heat conductors Malleable (can be moulded into shape) Non-malleable (brittle in their solid form) Ductile (can be pulled into wires) Non-ductile Shiny (when freshly cut) Not usually shiny Many have high melting points Low melting point Many have high boiling points Low boiling point

Metals The key to understanding a metal’s properties lies in its structure positive ions A metal structure is an ordered pattern of positive ions in a ‘sea’ of negative electrons. free electrons Ductility 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 Electrons act as a type of lubricant between the layers of ions. This explains why it’s possible to pull metals to form wires. 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).

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. Metallic glasses are three times as strong as steel and ten times more flexible, making them ideal for use as golf clubheads.

BONDING Ionic Structures Sodium chloride is formed when atoms of sodium bond with atoms of chlorine. Cl- Na+ +) [2. 8] Sodium atom ion (Na) [2. 8. 1] -) [2. 8. 8] Chlorine ion Chloride atom (Cl(Cl) [2. 8. 7] 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-.

BONDING Ionic Structures Na+ Cl- Sodium ion (Na+) [2. 8. ] Sodium chloride (salt) Chloride ion (Cl-) [2. 8. 8]

BONDING Ionic Structures So there are two types of ion: - 1) Positive ion (cation) – the atom has lost an electron or electrons. 2) Negative ion (anion) – the atom has gained electron(s). The ions attract and the attraction is ionic bonding. 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 Molecular structure of Sodium Chloride Six Sodium ions cluster around one Chloride ion

Properties of Ionic Compounds PROPERTY DUE TO High melting point Strong electrostatic forces of attraction between the ions. A lot of energy is needed to break them. Solid ionic compounds do not conduct electricity. The ions are held in fixed positions, and are not free to move. Molten ionic compounds conduct electricity. Melting has separated the ions so that they can move past each other.

BONDING Covalent 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. H 2 • Small molecules of compounds, e. g. HCl • Giant molecules of elements, e. g. diamond and graphite • Giant molecules of compounds, e. g. Si. O 2

BONDING Covalent molecules Some elements form covalent compounds. This happens as atoms share electrons. H Cl Chlorine atom (Cl) [2. 8. 7] Hydrogen atom (H) [1] Molecule of hydrogen chloride (HCl) 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).

Properties of molecular covalent compounds Melting points Low (attraction between molecules is weak) Physical state at room temperature Gases or liquids with low boiling points or solids with low melting points (weak forces of attraction between molecules) Electrical conductivity Do not conduct electricity (the molecules have no charge) Solubility in water Most are insoluble in water

An exercise to recognise atomic or covalent bonds. (Only the outer shell is shown in the diagrams) H Ca 2+ F 2 ionic H covalent O H covalent Cl Cl H Mg 2+ Cl-2 ionic covalent O H Cu N H H covalent Show the answers Cu 2+ O 2 ionic

Giant Covalent Structures Comparing the properties of graphite and diamond 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. PROPERTY Appearance Hardness Conductivity Melting point Diamond Graphite Transparent crystals Grey/ black shiny solid Incredibly hard – used for cutting glass and in drill bits for drilling through rocks in the oil industry. Very soft – used as a lubricant. Also used to make pencils. Electrical insulator A non-metal that conducts electricity. Used for making electrodes. Very high – over 3500°C. Very high – over 3600°C.

An explanation of the properties of diamond and graphite Diamond 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. 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 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.

The future, and other forms of carbon Whilst experimenting with Fullerene C 60, it was found that other structures of carbon could be formed. One of them is seen below: Fullerene C 60 The carbon atoms are bonded covalently into a football shape. Carbon Nanotube The nanotube is like rolled graphite. 1) It conducts electricity 2) It’s very small – 10, 000 times thinner than a human hair Nanotube 3) Crystals can be grown inside it Human hair 4) They may solve the problem of how to produce smaller circuits, where they might replace wires.