o level chemistry notes

Key things to study for each topic in O levels Disclaimer: This is meant as a summary so not every thing that could possibly come out in your exams may be included. This is also a work in progress so there may be errors or items that are left out by accident. Atomic structure Structure of atom Subatomic particle Symbol Relative charge Relative mass Proton p +1 1 Neutron n 0 1 electron e –1 Isotopes Definition of isotopes: Isotopes are atoms of the s ame element with the same number of protons, but different number of neutrons Calculation of relative atomic mass Q: If chlorine has 2 isotopes with relative masses of 35 and 37 and relative abundance of 75% and 25% respectively, calculate the relative atomic mass of chlorine. A: Relative atomic mass = 37 x 0.25 + 35 x 0.75 = 35.5 Calculation of relative abundance Q: If boron has 2 isotopes with relative masses of 10 and 11, given that boron has a relative atomic mass of 10.8, calculate the relative abundance of boron-10 and boron-11. A: Let the relative abundance of boron-10 be x 10x + 11(1 – x) = 10.8 x = 0.2 Therefore relative abundance of boron-10 is 20% and relative abundance of boron-11 is 80%.

Chemical bonding Template for answering common chemical bonding questions General template 1. State the structure 2. Describe the structure 3. Relate the relevant part of the structure to the physical property specified in the question Structure Simple covalent Giant covalent Giant Ionic lattice Giant Metallic Melting and boiling points • (substance) has a simple covalent structure. • It consists of discrete molecules held together by weak Van der Waals’ forces of attraction. • Very little energy is required to overcome these forces and (substance) has low melting and boiling point. Diamond • Diamond has a giant covalent structure • Each carbon atom is covalently bonded to 4 other carbon atoms in a giant covalent network. • These strong covalent bonds require large amount of energy to overcome. Graphite • Graphite has a giant covalent structure. • Each carbon atom is covalently bonded to 3 other carbon atoms in a giant covalent network. • These strong covalent bonds require large amount of energy to overcome. • (substance) has a giant ionic structure. • It is held together by strong electrostatic forces of attraction between oppositely charged ions in a giant ionic lattice. • A lot of energy is required to overcome these forces and (substance) has high melting and boiling point. • (substance) has a giant metallic structure. • It is held together by strong electrostatic forces of attraction between the positively charged cations and the ‘sea of delocalized’ electrons • A lot of energy to overcome those forces. Hence it has a high melting and boiling point.

Electrical conductivity • (substance) has a simple covalent structure. • It consists of molecules that are