This compilation covers the full Secondary 2 Science year. It starts with the structure of atoms and the formation of ions. It then covers forces, pressure, energy and heat transfer, followed by chemical changes. It ends with the biology chapters on ecosystems, digestion, transport systems and sexual reproduction.
Each chapter pairs key definitions with likely exam questions and model answers. There are also step-by-step answering templates for explain-type questions on conduction, convection and radiation, so students can revise every topic before the end-of-year examination.
What these notes cover
- •Structure of atoms and electronic configuration
- •Isotopes and ions
- •Mass, weight and density
- •Turning effect of forces and pressure
- •Forms of energy and conservation of energy
- •Conduction, convection and radiation
- •Physical and chemical changes
- •Acids, alkalis and the pH scale
- •Tests for gases
- •Interactions with ecosystems
- •Digestive system and transport systems in living things
- •Sexual reproduction
Key definitions
- Isotopes
- Isotopes are atoms of the same element that have the same number of protons (and electrons) but different numbers of neutrons, e.g. chlorine-35 and chlorine-37. They have the same chemical properties because they have the same number of valence electrons.
- Cation and anion
- A cation is a positively charged ion formed by the loss of electrons. An anion is a negatively charged ion formed by the gain of electrons. Metals tend to form cations because they have only a few valence electrons to lose.
- Thermal equilibrium
- Thermal equilibrium is the state in which two objects are at the same temperature, so there is no net transfer of thermal energy between them.
- Convection
- Convection is the transfer of heat from one part of a fluid to another by a circulating movement due to differences in density. It does not occur in solids, because their particles transfer heat without moving from place to place.
- Chemical change
- A chemical change is one in which new substances are formed, and it is hard to reverse. In a physical change, no new substances are formed, and the change can be reversed by separation techniques.
Key formulas
Mass (nucleon) number
mass number = number of protons + number of neutrons
The proton (atomic) number is the number of protons. Protons and neutrons are in the nucleus. In an electrically neutral atom, the number of electrons equals the number of protons.
Weight
W = m × g
W = weight in N, m = mass in kg and g = gravitational field strength in N/kg (10 N/kg on Earth, 1.6 N/kg on the Moon). Mass stays the same everywhere, but weight changes.
Mass from density
m = D × V
D = density and V = volume. Density is how much mass is packed into a space. A density in g/cm³ multiplied by a volume in cm³ gives a mass in g.
Pressure
p = F ÷ A
p = pressure in Pa (N/m²), F = force in N and A = area in contact in m². For an object resting on a surface, the force equals its weight. Pressure increases when the force increases or the area in contact decreases.
Unit conversions
1 cm² = 0.0001 m²; 1 cm³ = 0.000001 m³; 1 g/cm³ = 1000 kg/m³
Convert every quantity to SI units before calculating weight or pressure.
Reactions of acids
acid + alkali → salt + water; acid + reactive metal → salt + hydrogen; acid + metal carbonate → salt + water + carbon dioxide
Naming the salt: hydrochloric acid gives a chloride, nitric acid gives a nitrate and sulfuric acid gives a sulfate.
Worked example
An object has a volume of 200 cm³ and a density of 85 g/cm³. Find its weight where the gravitational field strength is 10 N/kg.
- 1Find the mass using m = D × V: m = 85 × 200 = 17 000 g.
- 2Convert the mass to kilograms: 17 000 g ÷ 1000 = 17 kg.
- 3Find the weight using W = m × g: W = 17 × 10 = 170 N.
Watch out: Mass must be in kg, not g, before it is substituted into W = m × g.
Common mistakes
Mixing up isotopes and ions
Wrong: Describing an ion as an atom with a different number of neutrons.
Right: Isotopes have the same proton number but different neutron numbers. Ions have the same proton and neutron numbers but a different number of electrons.
Calculating pressure in non-SI units
Wrong: Substituting mass in grams and area in cm² straight into p = F ÷ A.
Right: Convert the mass to kg and find the force using W = m × g. Then convert the area to m² (1 cm² = 0.0001 m²) and use p = F ÷ A to get the pressure in Pa.
Not stating the definition
Wrong: Answering only 'it is a physical change'.
Right: State the definition as well: a physical change is one in which no new substances are formed.
Questions students ask
What is the difference between mass and weight in Sec 2 Science?
Mass is the amount of matter in an object. Its SI unit is the kilogram, it is measured with an electronic or beam balance and it does not change. Weight is the gravitational force acting on an object. It is measured in newtons with a spring balance and found using W = m × g, so it is different on the Moon even though the mass stays the same.
Why are sodium and potassium in the same group?
Sodium has the electronic configuration 2.8.1 and potassium has 2.8.8.1, so both have one valence electron. The number of valence electrons matches the group number, which places both in Group 1. Elements in the same group form ions with the same charge.
How do you test for carbon dioxide, hydrogen, oxygen and ammonia?
Carbon dioxide forms a white precipitate in limewater. Hydrogen gives a 'pop' sound with a lighted splint, and oxygen relights a glowing splint. Ammonia turns damp red litmus paper blue and has a pungent smell.
Why are metals good conductors of heat?
Metals have free electrons, which transfer thermal energy more rapidly than in other materials. Heat is conducted through metals in two ways: by vibration of particles and by free electron diffusion. Poor conductors of heat, such as air, are called insulators.
In the full PDF
- •Full chapters on interactions with ecosystems, the digestive system, transport systems in living things and sexual reproduction
- •Atoms and molecules quiz with model answers
- •Answering templates and a flashcard question bank for conduction, convection and radiation
- •Practice questions on acid, metal and water reactions with balanced chemical equations
- •Mid-year quiz on chemical changes and end-of-year revision questions covering all topics
- •Further questions on pressure, turning effect and energy conversion