GCSE Chemistry Paper 1: Key Notes for Revision

Atomic Structure Basics

Think of an atom as a tiny solar system with the nucleus at its centre, containing protons and neutrons. Electrons whiz around this nucleus in shells, similar to planets orbiting the sun.

Here's what you need to remember: protons carry a positive charge $+1$, electrons are negative $-1$, and neutrons are neutral (0). Protons and neutrons are hefty with a relative mass of 1, whilst electrons are practically weightless.

The whole atom has a radius of just 0.1nm, but here's the mad bit - the nucleus is 100,000 times smaller than the entire atom! Most of an atom is actually empty space.

Quick Tip: When atoms lose electrons, they become positive ions. When they gain electrons, they become negative ions. It's all about the electron balance!

Elements, Isotopes and Calculating Mass

Every element on the periodic table has an atomic number (number of protons) and a relative atomic mass. Using lithium as an example: it has 3 protons, so its atomic number is 3.

Isotopes are different versions of the same element - they have identical protons but different numbers of neutrons. Think of them as siblings who look similar but aren't identical twins.

To calculate relative atomic mass, you'll use the abundance (how common each isotope is). For copper: multiply each isotope's mass by its percentage, add them together, then divide by 100. So (69.2 × 63) + (30.8 × 65) ÷ 100 = 63.6.

Compounds like H₂SO₄ always have the same proportions of elements - 2 hydrogen, 1 sulfur, 4 oxygen atoms. Mixtures, however, can be easily separated because the substances aren't chemically bonded together.

Remember: Molecules need at least 2 atoms held by chemical bonds, whilst mixtures are just substances hanging out together without bonding!