1. Higher Chemistry Unit 1(c) Density, melting points and boiling points

2. After today’s lesson you should be able to: Give two ways in which Mendeleev arranged the elements in the Periodic Table Explain what is meant by the density of a substance. Give the general trend in densities across a period and down a group. Give the general trend in melting and boiling points across a period and down a group. Explain this trend in relation to the bonding of the element.

3. Densities of the elements The density of an element is its mass per unit volume. The units of density are usually given as gcm -3. Elements with high densities have ‘heavy’ atoms packed closely together Elements with low densities have ‘light’ atoms spread out

4. Trends in densities within the periodic table Exercise Arrange the cards in order of their position in the Periodic Table. What trend do you see: (a) across a period? (b) down a group?

5. Melting and Boiling Points When a substance melts it changes from a solid to a liquid. When a substance boils it changes from a liquid to a gas.

6. Trends in Melting and Boiling points within the Periodic Table Exercise Draw a bar chart to show both the melting and boiling points of the elements in Period 3 of the Periodic Table.

7. Bonding If an element has low melting and boiling points it contains weak bonds. If an element has high melting and boiling points it contains strong bonds.