Chemistry and Our Earth

The Structure of the Earth

• The Earth is composed of four main layers: the inner and outer core, the mantle, and the crust.
• The core is primarily made up of nickel and iron, with the outer core being molten and the inner core solid due to extreme pressure.
• Moving away from the core, the mantle is a hot, semi-solid layer that is responsible for the motion of tectonic plates due to convection currents.
• The crust is the outermost layer where we live. It's composed of oxygen, silicon, aluminium, iron, calcium, sodium, potassium and magnesium.

Rock Cycle and Plate Tectonics

• The rock cycle is a continuous process that transforms rocks from one type to another. It involves processes such as weathering, heat, pressure, cooling, and melting.
• Types of rocks include igneous (formed from cooled magma or lava); sedimentary (formed from accumulations of small particles and organic matter); metamorphic (formed when either igneous or sedimentary rocks are subjected to heat and pressure).
• Plate tectonics refers to the movement of seven major and numerous minor geological plates on the earth's surface.

Atmospheric Gases and Climate Change

• The Earth's atmosphere is composed primarily of nitrogen (78%) and oxygen (21%) with small amounts of argon, carbon dioxide and other gases.
• Greenhouse gases such as carbon dioxide, methane, and water vapour trap heat in the atmosphere, causing the Earth to warm. This is known as the greenhouse effect.
• Climate change refers to any significant changes in measures of climate (such as temperature, precipitation, or wind) lasting for an extended period (decades or longer). Human activities, especially the burning of fossil fuels, are a major contributor to this change.

Elements, Atoms and Compounds

• An element is a pure substance that cannot be broken down into simpler substances by chemical reactions. Each element is identified by its unique atomic number, which is the number of protons in its nucleus.
• An atom is the smallest unit of an element that maintains the properties of that element. It consists of a nucleus (containing protons and neutrons) and surrounding electrons.
• A compound is a substance formed when two or more elements chemically combine in a fixed ratio. For example, water (H2O) is a compound made from hydrogen and oxygen.

Chemical Reactions

• Chemical reactions are processes that transform one set of substances into a new set of substances.
• Indications of a chemical reaction include colour change, formation of gas or a precipitate, change in temperature, or light being produced.
• Balancing chemical equations is the process of ensuring that the number of atoms of each element is the same on both the reactant and product sides of a chemical equation.

Acids, Bases, and pH

• Acids are substances that release hydrogen ions (H+) when dissolved in water. Common examples include sulphuric acid, hydrochloric acid and nitric acid.
• Bases are substances that can accept hydrogen ions or donate hydroxide ions (OH-). Examples include sodium hydroxide, ammonium hydroxide.
• The pH scale measures the acidity or basicity of a solution, ranging from 0 (very acidic) to 14 (very basic). A pH of 7 means the solution is neutral.

Periodic Table

• The Periodic Table is a chart that organises elements according to their atomic number, electron configuration, and recurring chemical properties. It consists of groups (columns) and periods (rows).
• Group 1 elements are known as alkali metals and are highly reactive, while Group 0 elements, known as noble gases, are inert.
• Across a period, atomic radius generally decreases and electronegativity increases, while down a group, atomic radius increases and ionisation energy decreases.