11-13-2025, 01:41 PM
Chemistry Basics Pack — GCSE-Friendly Introduction
A simple, clear starter guide to chemistry.
Perfect for beginners, GCSE students, and anyone wanting a quick understanding of atoms, bonding, reactions, and the periodic table.
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1. Atoms, Elements & Compounds
Atom: the smallest particle of an element.
Element: a substance made of only one type of atom.
Examples: oxygen (O), carbon ©, hydrogen (H).
Compound: two or more elements chemically bonded.
Examples:
• H₂O (water)
• CO₂ (carbon dioxide)
• NaCl (salt)
Molecule: a group of atoms bonded together.
All molecules are compounds except those made of a single element (e.g. O₂).
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2. Structure of the Atom
• Protons → positive charge (+1)
• Neutrons → no charge
• Electrons → negative charge (–1)
Structure:
• protons & neutrons in the nucleus
• electrons in shells around the nucleus
Atomic number = number of protons
Mass number = protons + neutrons
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3. Ions
Ions form when atoms gain or lose electrons.
• Gain electrons → negative ion
• Lose electrons → positive ion
Examples:
• Na → Na⁺ (loses 1 electron)
• Cl → Cl⁻ (gains 1 electron)
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4. The Periodic Table (Basics)
• Group number = number of electrons in outer shell
• Period = number of shells
• Metals on the left, non-metals on the right
Important groups:
• Group 1 → Alkali metals
• Group 7 → Halogens
• Group 0 → Noble gases (unreactive)
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5. Types of Bonding
1. Ionic Bonding
Between metal + non-metal.
Electrons transferred.
Forms ions.
Example:
Na⁺ and Cl⁻ → NaCl
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2. Covalent Bonding
Between two non-metals.
Electrons shared.
Examples:
• H₂O
• CO₂
• O₂
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3. Metallic Bonding
Between metal atoms.
Positive ions in a “sea” of delocalised electrons → conducts electricity.
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6. States of Matter
Solid → Liquid → Gas
Melting, boiling, evaporating.
Gas → Liquid → Solid
Condensing, freezing.
Particle spacing:
• solids: close & fixed
• liquids: close but move
• gases: very far apart
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7. Chemical Reactions
Signs of a reaction:
• colour change
• temperature change
• fizzing / gas produced
• solid forms (precipitate)
• new substance formed
Word equation example:
magnesium + oxygen → magnesium oxide
Symbol example:
2Mg + O₂ → 2MgO
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8. Conservation of Mass
Mass is always conserved in a chemical reaction.
Total mass of reactants = total mass of products
No atoms are created or destroyed.
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9. Acids, Alkalis & pH
• pH < 7 → acid
• pH = 7 → neutral
• pH > 7 → alkali
Examples:
• HCl (hydrochloric acid)
• NaOH (sodium hydroxide)
Neutralisation:
acid + alkali → salt + water
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10. Common GCSE Equations
• acid + metal → salt + hydrogen
• acid + carbonate → salt + water + CO₂
• acid + alkali → salt + water
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11. Common Mistakes
❌ Mixing up atoms vs molecules
✔ Atoms = single particles, molecules = bonded groups
❌ Thinking electrons live in the nucleus
✔ They orbit in shells
❌ Confusing ionic and covalent bonding
✔ Ionic = transfer of electrons, covalent = sharing
❌ Believing mass changes in reactions
✔ Mass is conserved
❌ Using pH values backwards
✔ Low pH = strong acid
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Summary
This pack covers the essentials:
• atoms & ions
• bonding
• states
• reactions
• periodic table
• equations
• pH
Master these and GCSE chemistry becomes far easier.
A simple, clear starter guide to chemistry.
Perfect for beginners, GCSE students, and anyone wanting a quick understanding of atoms, bonding, reactions, and the periodic table.
-----------------------------------------------------------------------
1. Atoms, Elements & Compounds
Atom: the smallest particle of an element.
Element: a substance made of only one type of atom.
Examples: oxygen (O), carbon ©, hydrogen (H).
Compound: two or more elements chemically bonded.
Examples:
• H₂O (water)
• CO₂ (carbon dioxide)
• NaCl (salt)
Molecule: a group of atoms bonded together.
All molecules are compounds except those made of a single element (e.g. O₂).
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2. Structure of the Atom
• Protons → positive charge (+1)
• Neutrons → no charge
• Electrons → negative charge (–1)
Structure:
• protons & neutrons in the nucleus
• electrons in shells around the nucleus
Atomic number = number of protons
Mass number = protons + neutrons
-----------------------------------------------------------------------
3. Ions
Ions form when atoms gain or lose electrons.
• Gain electrons → negative ion
• Lose electrons → positive ion
Examples:
• Na → Na⁺ (loses 1 electron)
• Cl → Cl⁻ (gains 1 electron)
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4. The Periodic Table (Basics)
• Group number = number of electrons in outer shell
• Period = number of shells
• Metals on the left, non-metals on the right
Important groups:
• Group 1 → Alkali metals
• Group 7 → Halogens
• Group 0 → Noble gases (unreactive)
-----------------------------------------------------------------------
5. Types of Bonding
1. Ionic Bonding
Between metal + non-metal.
Electrons transferred.
Forms ions.
Example:
Na⁺ and Cl⁻ → NaCl
---------------------------------------------------
2. Covalent Bonding
Between two non-metals.
Electrons shared.
Examples:
• H₂O
• CO₂
• O₂
---------------------------------------------------
3. Metallic Bonding
Between metal atoms.
Positive ions in a “sea” of delocalised electrons → conducts electricity.
-----------------------------------------------------------------------
6. States of Matter
Solid → Liquid → Gas
Melting, boiling, evaporating.
Gas → Liquid → Solid
Condensing, freezing.
Particle spacing:
• solids: close & fixed
• liquids: close but move
• gases: very far apart
-----------------------------------------------------------------------
7. Chemical Reactions
Signs of a reaction:
• colour change
• temperature change
• fizzing / gas produced
• solid forms (precipitate)
• new substance formed
Word equation example:
magnesium + oxygen → magnesium oxide
Symbol example:
2Mg + O₂ → 2MgO
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8. Conservation of Mass
Mass is always conserved in a chemical reaction.
Total mass of reactants = total mass of products
No atoms are created or destroyed.
-----------------------------------------------------------------------
9. Acids, Alkalis & pH
• pH < 7 → acid
• pH = 7 → neutral
• pH > 7 → alkali
Examples:
• HCl (hydrochloric acid)
• NaOH (sodium hydroxide)
Neutralisation:
acid + alkali → salt + water
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10. Common GCSE Equations
• acid + metal → salt + hydrogen
• acid + carbonate → salt + water + CO₂
• acid + alkali → salt + water
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11. Common Mistakes
❌ Mixing up atoms vs molecules
✔ Atoms = single particles, molecules = bonded groups
❌ Thinking electrons live in the nucleus
✔ They orbit in shells
❌ Confusing ionic and covalent bonding
✔ Ionic = transfer of electrons, covalent = sharing
❌ Believing mass changes in reactions
✔ Mass is conserved
❌ Using pH values backwards
✔ Low pH = strong acid
-----------------------------------------------------------------------
Summary
This pack covers the essentials:
• atoms & ions
• bonding
• states
• reactions
• periodic table
• equations
• pH
Master these and GCSE chemistry becomes far easier.