Secondary 4 End of Year Examinations
Chemistry Revision Notes
List of topics:
1. Atomic Structure
2. Separation Techniques
3. Chemical Bonds and Bonding (Ionic, Covalent)
5. Properties and structures of compounds
6. Qualitative Analysis
7. Acids, Bases and Salts
8. Chemical Periodicity
9. Chemical Calculations
10. Air and Environment
11. Electrochemistry (Including Redox reactions)
13. Rates of Reaction
14. Chemical Equilibrium
15. States of Matter
16. Organic Chemistry
1) Atomic Structure
(a) Model of Atom
The model of atom consists of 3 subatomic particle, namely the protons, electrons and neutrons. Of which, the protons and neutrons are found within the nucleus of the atom. As such, the nucleus of the atom has a positive charge, and most of the mass of the atom is located in the nucleus due to the insignificance of the weight of electrons. Surrounding the nucleus is a cloud of electrons, which move randomly around orbitals and sub orbitals at nearly the speed of light. Other than this, most of the atom is empty space. The overall atom is electrically neutral, as the number of protons is equal to the number of electrons, while the nucleus carries no charge.
(b) Sub atomic particles
• Protons, which carries a positive electric charge
• Neutrons, which has the same mass as a proton but carried no charge • Electrons, which carries a negative electric charge
| |relative mass |relative charge | |Proton |1 |+1 | |Neutron |1 |0 | |Electron |1/1836 |-1 |
(c) Behaviour of sub atomic particles in electric field
• Protons are positively charged and so would be deflected on a curving path towards the negative plate. • Electrons are negatively charged and so would be deflected on a curving path towards the positive plate. • Neutrons don't have a charge, and so would continue on in a straight line. 1) If particles have same energy:
• Protons are deflected on a curved path towards the negative plate. • Electrons are deflected on a curved path towards the positive plate. • Neutrons continue in a straight line.
The amount of deflection is exactly the same in the electron beam as the proton beam if the energies are the same - but, of course, it is in the opposite direction.
2) If particles have same speed:
• Protons are deflected on a curved path towards the negative plate, but are attracted more quickly • Electrons are deflected on a curved path towards the positive plate, but are attracted more slowly • Neutrons continue in a straight line.
If the electrons and protons are travelling with the same speed, then the lighter electrons are deflected far more strongly than the heavier protons.
(d) Numbers of protons, neutrons and electrons
1) Atom number/ Proton number ( Gives the number of protons in an atom of particular element 2) Mass number/ nucleon number ( Gives the sum of number of protons and neutrons 3) Number of electrons ( As aforementioned, number of electrons is equal to the number of protons, since the atom is electrically neutral.
Isotopes are atoms of the same element which have the same atomic number but different mass numbers, as they have the same number of protons but different numbers of neutrons. The relative abundance of an element is the approximate nucleon number of an element taking into consideration all available isotopes:
(f) Atomic Orbitals and sub orbitals
Electrons in fact inhabit regions of space known as orbitals. The Heisenberg...