1. Unit: Matter and Chemical Bonding 2.3 Classifying Chemical Compounds: Properties of Ionic and Covalent Compounds

2. Properties of Ionic and Covalent Compounds

3. PROPERTY 1: Melting/Boiling PointsWHAT WE ALREADY KNOW: • The melting point of a compound is the temperature at which it changes from a solid to a liquid at STP. • The boiling point of a compound is the temperature at which it changes from a liquid to a gas at STP.

4. PROPERTY 1: Melting/Boiling Points • A low melting or boiling point means small amounts of kinetic energy are enough for a particle to break away from its neighbours. the forces between the particles are weak. • A very high melting or boiling point means the particles must have a very large amount of kinetic energy to break away  the forces between the particles are strong

5. NaCl, Table Salt: An Ionic Compound • Sodium chloride=Crystalline solid at room T. • Very high melting point, at 801 ◦C • Easily dissolved in water and great electrical conductor. (Ex. Sea water) • Uses: flavouring food (can cause blood pressure), melts ice in the winter

6. High Melting and Boiling Points = IONIC COMPOUNDS This means that the attractive electrostatic forces between oppositely charged particles create very strong bonds. The crystal lattice arrangement of ionic compounds means that multiple ions are involved in this interaction simultaneously, which results in a great force.

7. Medium Melting and Boiling Points = COVALENT COMPOUNDS with POLARITY The medium strength of the polar covalent bonds is a result of the dipole-dipole force. • This is the attractive force between the positive end of one molecule and the negative end of another molecule.

8. Carbon Dioxide: A Covalent Compound • Carbon dioxide = gas at room T but under certain T’s and P’s can be liquid. • Very low melting point, at -79 ◦C • Easily somewhat soluble in water and a weak electrical conductor. • Uses: cellular respiration and photosynthesis

9. Low Melting and Boiling Points = NON-POLAR COVALENT COMPOUNDS • Although non-polar molecules have no distinct separation of charge, it is still possible for the positive nuclei of atoms in one molecule to attract the electrons of a neighbouring molecule.  These forces are very weak!

10. PROPERTY 2: Water solubility • The partially positive H in water is attracted to negative ions of an ionic compound or the partially negative atom of a polar compound. • The partially negative O in water is attracted to the positive ions of an ionic compound or the partially positive atom of a polar compound. IONIC AND POLAR COVALENT COMPOUNDS ARE WATER SOLUBLE. NON-POLAR COVALENT COMPOUNDS ARE NOT WATER SOLUBLE.

11. PROPERTY 3: Electrical Conductivity Electrical conductivity is the ability of a substance to allow an electric current to pass. A substance is conductive if charges can move independently of one another. This is only possible for ionic compounds in the liquid state or dissolved in water. For this reason they are called electrolytes Since in covalent compounds , electrons do not leave an atom completely these compounds do not conduct electricity when in liquid state. They are called non-electrolytes.

12. Conductivity with a Multimeter • http://www.youtube.com/watch?v=kSPDjAhl1Qc • Salt • Sugar

13. Consider the following: • Write the formula next to each compound. • Sort the compounds according to their boiling points. • What do you notice?

14. “ThoughtLab: Ionic Or Covalent?” Imagine that you are a chemist. A colleague has just carried out a series of tests on the following compounds: Ethanol (clear, liquid) Carbon tetrachloride (clear, liquid) Glucose (white, powder, solid) Sodium chloride – table salt (white, crystalline solid) Water (clear, liquid) Potassium permanganate (bluish-purple, crystalline solid) Unfortunately your colleague labelled the tests by sample number and not name. Use the properties of the compounds to identify them.