Higher Chemistry Bonding and Properties NEW LEARNING Grouping elements by bonding and structure – focus on Titanium Grouping compounds and elements by bonding structure and properties. Periodic trends REVISION Elements are the simplest substances and consist of one type of atom. They are arranged in the Periodic table in increasing atomic number.

Lesson 1: Bonding and Properties Today we will learn to Explain the properties of substances based on their bonding type. We will do this by Investigating melting point and solubility for a variety of substances, including those involved in extracting titanium. We will have succeeded if We can correctly identify bonding type from properties..

Bonding and Properties Melting & Boiling Points When metals melt, metallic bonds are broken. In the case of ionic lattices it is the ionic bonds that are broken. In covalent networks it is the covalent bonds that are broken. However in covalent molecules it is the Van der Waal forces that are broken. The stronger the bond or force that needs to be broken to get the substance to melt or boil, the higher its melting or boiling point. Viscosity The stronger the force of attraction between molecules the greater the viscosity or thickness of a liquid. Electrical Conductivity In order for something to be able to conduct it must contain charged particles (electrons or ions) that are free to move. Solubility As a rule of thumb, in terms of solubility, “like dissolves like”. In other words ionic and polar molecules tend to dissolve in polar solvents and non-polar molecules tend to dissolve in non-polar solvents. Metals and covalent networks are insoluble but metals can sometimes react to form soluble products.

Bonding, Solubility and Solutions Ionic lattices and polar covalent molecular compounds tend to be: Soluble in water and other polar solvents, due to the attraction between the opposite charges. Insoluble in non-polar solvents, as there is no attraction between the ions and the solvent molecules. e.g. when ionic compounds dissolve in water the lattice is broken up and the ions are surrounded by water molecules. - + - + Water molecule Ionic lattice Hydrated ions - - + + -ve ions attracted to +ve ends of water molecule +ve ions attracted to –ve ends of water molecule

Non-polar covalent molecular substances tend to be: Soluble in non-polar solvents like carbon tetrachloride or hexane. Insoluble in water and other polar solvents as there are no charged ends to be attracted. ‘Like dissolves like’

Bonding and Solubility

Bonding and Properties of Compounds Compounds can be split into 3 main groups, depending on their bonding, structure and properties: Ionic Lattice Structures Covalent Network Structures Covalent Molecular Structures 1. Ionic Lattice Structures All ionic compounds are solids at room temp so have high melting and boiling points. This is because the ionic bonds holding the lattice together are strong and a lot of energy is required to break them. (image from bbc.co.uk)

The size of the ions will effect the strength of the ionic bond and how the ions pack together. E.g. NaF - m.p 1000oC, NaI - 660oC. Ionic compounds conduct electricity when dissolved in water or when molten as the ions are free to move. Electrolysis of an ionic solution or melt causes a chemical change at the electrodes. They do not conduct when solid as the ions are ‘locked in the lattice and cannot move to carry the current.

2. Covalent Network Structures Covalent networks have very high melting and boiling points as many strong covalent bonds need to be broken in order to change state. They can also be very hard. E.g. Silicon Carbide (SiC) – carborundum, similar structure to diamond = Carbon = Silicon Covalent Bond Tetrahedral shape The 4 carbon atoms are available to bond with another 4 silicon atoms resulting in a covalent network.

It has a high melting point (2700oC) SiC is used as an abrasive. Covalent network structures are usually non-conductors of electricity as they have no free moving charged particles.

3. Covalent Molecular Structures Usually have low melting and boiling points as there is little attraction between their molecules. E.g. Carbon dioxide CO2: m.pt -57oC (non-polar) Compounds with polar molecules may have slightly higher m.pts and b.pts than non-polar molecules due to permanent dipole-permanent dipole attractions. e.g. Iodine chloride Bromine I - Cl Br – Br b.pt 97oC b.pt 59oC When hydrogen bonds are present, the compounds will have a much higher m.pt and b.pt than other compounds of similar molecular size as more energy is required to separate the molecules. (see earlier note on hydrogen bonding – ethanol and ether)

Bonding and Properties Extracting titanium from its ore, rutile, involves a number of reactions and processes. Understanding the bonding types and the effect of the properties of substances was very important in working out this method.

Starter Task Complete Quick Test 5 in your booklet and we will review as a class. You have 10minutes! S3 Revision

Answers Quick Test 5 A 2. D 3. C 4. B 5. D 6. C S3 Revision

Lesson 2: Identifying Unknowns Today we will learn to Identify the bonding in unkown substances. We will do this by Investigating melting point and solubility for a variety of substances, and matching properties to the chemicals given. We will have succeeded if We can correctly identify bonding type from properties..

Identifying Unknowns Activity 1.15 Identifying Unknown Substances Challenge You will be given 15 substances labelled from A to O. Using the information given on the accompanying sheet and the results of any experiments you use to test the properties of the substances; you need to identify each substance, their bonding type and give a reason for your choice. In the first instance it is helpful to write down what you know about them what their likely properties will be.

Identifying Unknowns What can you easily test? copper chloride, silicon oxide (sand), sugar (C12H22O11), copper carbonate, oxygen, sodium chloride, iron, alcohol (C2H5OH), nickel chloride, polyethene ([-CH2-CH2-]n), sulfur, hydrogen, pentane (C5H12), calcium carbonate (chalk) copper. What can you easily test?

Identifying Unknowns