CHEMISTRY FORM 2
- 1.1 Structure of the atom
- 1.2 Atomic Number and Mass Number
- 1.3 Isotopes
- 1.4 Energy levels and electron arrangement
- 1.5 Development of the Periodic Table
- 1.6 Relative Atomic Mass and Isotopes
- 1.7 Ion Formation
- 1.8 Chemical Formulae
- 1.9 Chemical Equations
- 2.1 Alkali metals (Group I elements)
- 2.2 Alkali Earth Metals (Group II elements)
- 2.3 Halogens (Group VII elements)
- 2.4 Noble gases (Group VIII elements)
- 2.5 Properties and Trends Across the Periodic Table
- 3.1 Bond
- 3.2 Ionic bond
- 3.3 Giant ionic structure
- 3.4 Covalent bond
- 3.5 Co-ordinate bond
- 3.6 Molecular structures
- 3.7 Giant covalent structures
- 3.8 Metallic Bond
- 3.9 Types of bond across a period
- 3.10 Oxides of elements in Period 3
- 3.11 Chlorides of Period 3 elements
- 4.1 What is a salt?
- 4.2 Types of salt
- 4.3 Solubility of salts in water
- 4.4 Methods of preparing salts
- 4.4.1 Reacting a Metal with an Acid
- 4.4.2 Reacting an Acid with a Base (Neutralization)
- 4.4.3 Reacting an Acid with a Carbonate (or hydrogencarbonate of metal)
- 4.4.4 Combining elements Directly (Direct Combination of elements)
- 4.4.5 Precipitation (Double decomposition)
- 4.5 Action of heat on salts
- 4.6 Uses of salts
- 5.1 Electrical conduction
- 5.2 Electrical conductivity of molten substances
- 5.3 Electrical conductivity of substances in aqueous state
- 5.4 Electrolysis
- 5.5 Applications of electrolysis
- 6.1 Allotropes of carbon
- 6.2 Chemical properties of carbon
- 6.3 Carbon (IV) oxide
- 6.4 Carbon (II) oxide (CO)
- 6.5 Large scale production of sodium carbonate and sodium hydrogencarbonate
- 6.6 Effect of carbon (II) oxide and carbon (IV) oxide on the environment
- 6.7 Carbon cycle
Structure of the Atom, and the Periodic Table: Atomic Number and Mass Number
1.0 Structure of the Atom, and the Periodic Table
1.2 Atomic Number and Mass Number
Atomic number (A)
Each atom has protons in its nucleus. The number of protons in an atom is called atomic number (symbol = A). Atomic number is the number of protons in the nucleus of an atom. It is the atomic number that makes elements different. Atoms of the same element have the same number of protons or atomic number.
Questions 1.2 
- State the atomic numbers of the atoms A to E (not the actual symbols) in Figure 1.2.1.
- Group together the atoms which belong to (or represent) the same element. Use the letters only.
Figure 1.2.1: Atomic numbers
Answers to Questions 1.2 
Mass number (M)
Protons, neutrons and electrons are extremely small and light. Their masses are too small to measure directly using a weighing balance. Because they have nearly the same mass, each proton and neutron is assigned a mass of 1 unit. But, being much lighter, an electron is assigned a mass of 0 unit; so its mass is ignored.
Table 1.2.2: Assigned (relative) masses of sub-atomic particles
Because the actual mass of an atom depends on the number of protons and neutrons in it, we can conveniently represent the mass with the number of protons and neutrons, and call it mass number. Mass number is the sum of number of protons and neutrons in an atom. An atom with one proton and one neutron, for example, has a mass number of 2; that is, 1+1.
Questions 1.3(a)
- An atom X has 8 protons and 10 neutrons. What is its mass number?
- Element Y has 4 neutrons and a mass number of 7. Find its atomic number.
Answers to Questions 1.3(a)
Table 1.2.3 shows mass numbers of the first 10 elements.
Table 1.2.3: Mass numbers of the first 10 elements
