Yr 9 Chemistry Notes Cheat Sheet

Matter is everything that has mass and occupies space. It is made up of atoms.
Classification of matter includes:
- Elements: pure substances made from one type of atom. E.g. Sodium (Na).
- Compounds: substances made from more than one type of atom bonded together. E.g. Sodium hydroxide (NaOH).
- Mixtures: substances not chemically bonded and can be separated. E.g. Salt water (NaCl + H₂O).
The Periodic Table describes all known elements, arranged left to right and top to bottom in order of increasing atomic number (the number of protons).
- Columns refer to groups (families).
- Rows refer to periods.
Information on the Periodic Table:
- Atomic number: number of protons.
- Atomic mass: approximate total mass of an atom.
- Number of protons, neutrons, and electrons in a neutral atom.
Elements, Compounds, and Mixtures (recap):
- Element: pure substance with one type of atom (e.g. Na).
- Compound: two or more elements chemically bonded (e.g. NaOH).
- Mixture: no chemical bonding between components (e.g. salt water).

Atoms consist of three main subatomic particles: protons, neutrons, and electrons.
Protons and neutrons are located in the nucleus; electrons orbit the nucleus in electron shells.
Electron configurations follow shells numbered from the one closest to the nucleus outward.
Electron shells (as given in the notes):
- The first shell holds up to 2 electrons.
- The second shell holds up to 8 electrons.
- The third shell holds up to 8 electrons (as stated in the notes).
Electron shells are numbered from the shell closest to the nucleus outward.

In an isolated system, mass cannot be created or destroyed; it can be transformed from one form to another.

Counting atoms is a foundational concept in balancing chemical equations and understanding reactions. (Reference to a resource is provided in the notes.)

Acid–Metal reactions: acids react with metals to form a salt and hydrogen gas.
Identification of hydrogen gas: the pop test. If a lit splint is placed near the test tube and hydrogen gas is present, a squeaky pop is heard.

All chemical reactions either absorb energy (endothermic) or release energy (exothermic).
Endothermic: require energy input to proceed.
Exothermic: release energy to the surroundings.

Acids:
- pH between 0 and 7.
- Taste sour.
- Neutralize bases.
- React with metals to form hydrogen gas.
Bases:
- pH between 7 and 14.
- Taste bitter.
- Neutralize acids.
- React with acids to form salt and water (neutralisation).

Universal Indicator (UI):
- Colour in Acid: Red
- Colour at Neutral: Green
- Colour in Base: Blue
Litmus Paper:
- In acid: Red
- At neutral: Purple
- In base: Blue

Hydroxide ions (OH⁻) from the base react with hydrogen ions (H⁺) from the acid to produce water:
- $\mathrm{OH^-} + \mathrm{H^+} \rightarrow \mathrm{H_2O}$
The remaining ions form a salt.

The first part of the salt name comes from the base, the second from the acid.
Examples (as given):
- Sodium hydroxide + Hydrochloric acid → Sodium chloride
- Magnesium oxide + Nitric acid → Magnesium Nitrate
- Sodium hydroxide + Sulfuric acid → Sodium sulfate

Acids react with metal carbonates to form a salt, water, and carbon dioxide:
- General equation: $\text{Acid} + \text{Carbonate} \rightarrow \text{Salt} + \text{Water} + \text{CO}_2$

Limewater (calcium hydroxide solution) turns milky white in the presence of CO₂, indicating CO₂ production in the reaction.

Counting atoms reference: a linked resource is provided in the notes for deeper practice.
Real-world relevance (implied): acidity and basicity are important in chemistry labs, environmental science (acidic rain, rusting), medicine (neutralisation in antacids), and industry (salt production, metal corrosion).