Untitled Notes

Revision Booklet for Year 9 Higher - Paper 2

Section A - Chemistry

Group 7 Elements (Halogens)

Definition: Group 7 elements are known as halogens.
Electron Configuration: Each halogen has 7 electrons in their outer shell, which leads to similar reactivity.
Physical Characteristics:
- Halogens possess colored vapors.
- They exist as diatomic molecules, meaning they consist of pairs of atoms.
- Examples include:
- Fluorine (F2)
- Chlorine (Cl2)
- Bromine (Br2)

Atomic Models

J.J. Thompson - Plum Pudding Model
- Description: The atom is a ball of positive charge with electrons embedded within it.
- Characteristics:
  - No empty space exists within the atom.
  - Mass is uniformly distributed throughout.
Niels Bohr - Bohr's Model
- Description: Electrons orbit the nucleus in fixed paths.
- Features: Electrons are found at specified distances from the nucleus.

Ionic Bonding

Structure:
- Ionic substances form a giant ionic lattice.
Bonding:
- Strong electrostatic forces hold oppositely charged ions together in all directions, known as ionic bonding.
Sodium Chloride (NaCl):
- General Description:
- A metal atom transfers an electron to a non-metal atom.
- The metal atom loses electrons, forming a positive ion.
- The non-metal atom gains electrons, forming a negative ion.
Magnesium to Iodine Reaction:
- Magnesium (Mg) loses 2 electrons to form a positive ion (Mg²+).
- Two iodine (I) atoms each gain one electron to form negative ions (I⁻).

Covalent Bonding

Definition:
- Occurs between two or more non-metals.
Mechanism:
- Atoms share pairs of electrons to form strong covalent bonds.
Substance Types:
- Covalent substances may consist of small molecules or could form giant covalent structures (e.g., diamond, silicon dioxide).
Characteristics:
- Covalent bonds do not involve charged ions.

Dot and Cross Diagrams for Small Molecules

General Characteristics:
- These diagrams illustrate the sharing of electrons in covalent bonds.
Small Covalent Molecules:
- Examples with diagrams include:
- Hydrogen (H2)
- Chlorine (Cl2)
- Methane (CH4)
- Ammonia (NH3)
- Water (H2O)
- Oxygen (O2)

Properties of Small Covalent Molecules

Physical State:
- Generally gases or liquids with low melting and boiling points.
- Explanation:
  - Small covalent molecules possess weak intermolecular forces.
  - Little energy is required to overcome these forces.
- Larger molecules exhibit stronger intermolecular forces, resulting in higher melting and boiling points.
Electrical Conductivity:
- Small covalent molecules do not conduct electricity.
- Explanation:
  - Molecules lack an overall electric charge.

Giant Covalent Structures

Example: Diamond

Structure and Bonding:
- Formed solely from carbon atoms arranged in a regular tetrahedral network.
- Each carbon atom bonds to four others without free (delocalized) electrons.
Uses:
- Applications include laser beams, cutting tools, drills, and jewelry.
Properties of Diamond:

Hardness:
- Diamond's hardness is due to its giant covalent structure and strong covalent bonding.
Electrical Conductivity:
- Diamond does not conduct electricity owing to lack of delocalized electrons.
Melting Point:
- High melting point due to strong covalent bonds requiring significant energy to break.

Polymers

Definition:
- Polymers are long-chain molecules made from many smaller units called monomers.
Characteristics:
- Composed of large molecules linked through strong covalent bonds.
- Polymers typically have relatively strong intermolecular forces, making them solid at room temperature.
Concerns with Synthetic Polymers:
- Derived from non-renewable resources (crude oil).
- High energy consumption during production.
- Non-biodegradable, leading to landfill issues.

Section B - Physics

Circuit Symbols

Various symbols are used to represent components in electrical circuits.

Scalars and Vectors

Scalars:
- Scalars are quantities defined by magnitude alone without direction.
- Examples include: mass, temperature, distance, time, speed, and energy.
Vectors:
- Vectors possess both magnitude and direction.
- Examples include: force, displacement, velocity, and acceleration.

Forces

Definition:
- A force can be classified as either a push or pull and is not visible but can be observed through its effects.
**Effects of Forces on Objects: **
- Can alter an object's speed, direction of movement, or shape (e.g., stretching an elastic band).
Measurement:
- Measured using a force meter (or newton meter).
- The unit of measurement is Newton (N).

Types of Forces

Contact Forces:
- Include friction, air resistance, tension, normal contact force (opposing gravity), forward force, and upthrust (buoyant force).
Non-contact Forces:
- Include gravitational force, magnetic force, and electrostatic forces.

Changes in Energy Store

Kinetic Energy:
- Calculated using the equation: $E_k = 0.5 imes m imes v^2$
  - Where:
  - Kinetic energy, $E_k$ , is in joules (J)
  - Mass, $m$ , is in kilograms (kg)
  - Speed, $v$ , is in meters per second (m/s)
Elastic Potential Energy:
- Calculated using the equation: $E_e = 0.5 imes k imes e^2$
  - Where:
  - Elastic potential energy, $E_e$ , is in joules (J)
  - Spring constant, $k$ , is in newtons per meter (N/m)
  - Extension, $e$ , is in meters (m)
Gravitational Potential Energy:
- Calculated using the equation: $E_p = m imes g imes h$
  - Where:
  - Gravitational potential energy, $E_p$ , is in joules (J)
  - Mass, $m$ , is in kilograms (kg)
  - Gravitational field strength, $g$ , is in newtons per kilogram (N/kg)
  - Height, $h$ , is in meters (m)

Worked Example

Problem: A toast was raised by a spring and its change in gravitational potential energy was observed at 0.049 J with a mass of 0.050 kg in a gravitational field strength of 9.8 N/kg.

Identify Data:
- $E_p = 0.049 J$
- $m = 0.050 kg$
Write Equation:
- $E_p = m imes g imes h$
Substitute Values:
- $0.049 = 0.050 imes 9.8 imes h$
Solve for Height:
- $h = \frac{0.049}{(0.050 imes 9.8)}$
Calculation:
- Perform the calculation and include appropriate units.

Energy Resources

Non-renewable Resources:
- Resources that cannot be replenished and will eventually deplete.
- Examples:
  - Fossil Fuels (Coal, Oil, Natural Gas) - a chemical energy store.
  - Nuclear Power - energy derived from atomic structures.
  - Fossil Fuel Process:
  1. Combustion of fossil fuels generates steam.
  2. Steam drives turbines.
  3. Turbines spin generators, producing electricity.
  4. Transformers manage voltage levels entering the National Grid and homes.
- Advantages and Disadvantages of Fossil Fuels:
  - Advantages:
  - Readily available.
  - Relatively easy energy production.
  - Disadvantages:
  - Finite resources leading to depletion.
  - Rising fuel costs.
  - Greenhouse gas emissions upon combustion (CO2).
Using Nuclear Power:
- Process Overview:
  - Nuclear fission reactors utilize atomic nuclei processes but do not need in-depth understanding.
- Advantages and Disadvantages of Nuclear Power:
  - Advantages:
  - No CO2 emissions upon operation.
  - Does not produce SO2, preventing acid rain.
  - 1 kg of uranium yields millions of times more energy than 1 kg of coal.
  - Disadvantages:
  - Non-renewable, will eventually deplete.
  - High initial and decommissioning costs.
  - Generates hazardous radioactive waste.
  - Potential release of radioactivity into the environment.
Renewable Resources:
- Sources of energy that can be replenished.
- Types:
  - Biomass - combusted living/dead materials.
  - Geothermal - energy from radioactive rocks.
  - Hydro Electric Power - gravitational energy from water in high locations.
  - Solar - heat and light from the sun for thermal and electrical energy.
  - Tidal - harnessing gravitational energy from the moon.
  - Wind - kinetic energy from air movement due to uneven heating.
  - Waves - energy from wind's effect on water.
- Biofuels:
  - Fuels derived from plant matter (e.g., biodiesel, bioethanol).
- Advantages and Disadvantages of Biofuels:
  - Advantages:
  - Renewable.
  - Lower carbon emissions during combustion.
  - Reduces reliance on fossil fuels.
  - Disadvantages:
  - Requires farmland used for food production.
  - High labor demands for production.
  - Requires engine modification for uses.
- Energy from Wind:
  - Advantages and Disadvantages of Wind Power:
  - Advantages:
    - Renewable source.
    - Low operational costs.
  - Disadvantages:
    - High installation costs.
    - Creates visual pollution.
    - Noise pollution.
    - Reliability dependent on wind strength.
- Energy from Water:
  - Water energy is derived from gravitational storage in high locations.
  - Types:
  - Tidal:
    - Utilizes the moon’s gravitational pull to generate energy through dam systems.
  - Hydro Electric:
    - Water from high reservoirs is allowed to flow downward through turbines.
  - Advantages and Disadvantages of Water Power:
  - Advantages:
    - Renewable.
    - Low operational costs.
    - No emissions.
  - Disadvantages:
    - Visual pollution.
    - Potential habitat destruction from flooding.
    - Could obstruct shipping routes.
- Energy from the Sun:
  - Primary source of energy for all forms.
  - Advantages and Disadvantages of Solar Power:
  - Advantages:
    - Renewable.
    - Low service costs.
  - Disadvantages:
    - Low efficiency of solar cells.
    - High costs for efficiency improvements.
    - Weather dependency affects productivity.