Matter and their physical properties

science term test

Atomic Structure – Notes

Structure of an Atom
An atom is made up of three sub-atomic particles:
• Protons – Positive charge, present in the nucleus
• Neutrons – No charge, present in the nucleus
• Electrons – Negative charge, move around the nucleus in shells

 

The nucleus has an overall positive charge because it contains protons and neutrons.
Electrons have a negative charge.

Atomic Number (Z)

The atomic number is the number of protons present in an atom.
In a neutral atom, number of protons = number of electrons.
The atomic number identifies the element.

Mass Number / Nucleon Number (A)

The mass number is the total number of protons and neutrons in an atom.
Mass number = Number of protons + Number of neutrons

Atomic Notation

Atomic notation is written as:
A (mass number)
Z (atomic number)
X (chemical symbol)

Elements, Compounds and Mixtures

Element:
• Made of only one type of atom
• Represented by symbols
Examples: H, O, C, Fe

Compound:
• Formed by combination of two or more elements
• Elements combine in fixed proportions
• Represented by chemical formula
Examples: H2O, CO2

Mixture:
• Made of two or more elements or compounds
• Mixed in any proportion
• No chemical formula
Examples: Salt and water, air

IGCSE Chemistry – Acids, Bases and Salts 1. Acids

Acids are substances that produce hydrogen ions (H⁺) when dissolved in water.

Properties of Acids:
• Sour taste
• pH less than 7
• Turn blue litmus red
• React with metals to produce hydrogen gas
• React with bases to form salt and water

Examples of Acids:
• Hydrochloric acid (HCl)
• Sulfuric acid (H₂SO₄)
• Nitric acid (HNO₃)

2. Bases and AlkalisBases are substances that neutralise acids.
Alkalis are bases that dissolve in water and produce hydroxide ions (OH⁻).

Properties of Bases/Alkalis:
• Bitter taste
• Slippery feel
• pH greater than 7
• Turn red litmus blue

Examples:
• Sodium hydroxide (NaOH)
• Potassium hydroxide (KOH)

s

s

s

w