1|Page Cambridge IGCSE™ Chemistry 18/08/2024
Chemistry Notes Chapter 3 — Atomic Structure
Made by Kenneth E. Husin
Table of Contents
• Atomic Structure
• The Proton Number and Nucleon Number
o Introduction
o Proton Number
Different proton numbers
o Nucleon Number
o Representing the Proton and Nucleon Number
• Arrangement of Electrons in Atoms
o Outer Shell Electrons
• Isotopes
o Properties of Isotopes
o Calculating the Relative Atomic Masses of an Element
• Review Questions and Sources
Atomic Structure
All mater is made up of atoms. Atoms are �ny and can only be seen using an advanced
microscope that can magnify millions of �mes. However, atoms are made up of smaller par�cles. They
are called ‘subatomic par�cles’. These subatomic par�cles are protons, neutrons, and electrons.
An example of atoms having subatomic par�cles is Helium gas (He). Inside the Helium atom
are subatomic par�cles. The subatomic par�cles are:
- A proton
o Has a rela�ve charge of +1;
ATOMIC STRUCTURE KENNETH
, 2|Page Cambridge IGCSE™ Chemistry 18/08/2024
o Has a rela�ve mass of 1;
o Is represented by the symbol p.
- A neutron
o Has a rela�ve charge of 0;
o Has a rela�ve mass of 1;
o Is represented by the symbol n.
- An electron
o Has a rela�ve charge of -1;
1
o Has a rela�ve mass of ;
1840
o Is represented by the symbol e.
The proton and neutrons
- Are �ghtly packed together in the center of an atom;
- Together, they form the nucleus of the atom.
The electrons move rapidly around the nucleus.
The Proton Number and Nucleon Number
Introduction
- Helium (He)
o 2 protons
o 2 electrons
o 2 neutrons
- Lithium (Li)
o 3 protons
o 3 electrons
o 4 neutrons
- Beryllium (Be)
o 4 protons
o 4 electrons
o 5 neutrons
ATOMIC STRUCTURE KENNETH
Chemistry Notes Chapter 3 — Atomic Structure
Made by Kenneth E. Husin
Table of Contents
• Atomic Structure
• The Proton Number and Nucleon Number
o Introduction
o Proton Number
Different proton numbers
o Nucleon Number
o Representing the Proton and Nucleon Number
• Arrangement of Electrons in Atoms
o Outer Shell Electrons
• Isotopes
o Properties of Isotopes
o Calculating the Relative Atomic Masses of an Element
• Review Questions and Sources
Atomic Structure
All mater is made up of atoms. Atoms are �ny and can only be seen using an advanced
microscope that can magnify millions of �mes. However, atoms are made up of smaller par�cles. They
are called ‘subatomic par�cles’. These subatomic par�cles are protons, neutrons, and electrons.
An example of atoms having subatomic par�cles is Helium gas (He). Inside the Helium atom
are subatomic par�cles. The subatomic par�cles are:
- A proton
o Has a rela�ve charge of +1;
ATOMIC STRUCTURE KENNETH
, 2|Page Cambridge IGCSE™ Chemistry 18/08/2024
o Has a rela�ve mass of 1;
o Is represented by the symbol p.
- A neutron
o Has a rela�ve charge of 0;
o Has a rela�ve mass of 1;
o Is represented by the symbol n.
- An electron
o Has a rela�ve charge of -1;
1
o Has a rela�ve mass of ;
1840
o Is represented by the symbol e.
The proton and neutrons
- Are �ghtly packed together in the center of an atom;
- Together, they form the nucleus of the atom.
The electrons move rapidly around the nucleus.
The Proton Number and Nucleon Number
Introduction
- Helium (He)
o 2 protons
o 2 electrons
o 2 neutrons
- Lithium (Li)
o 3 protons
o 3 electrons
o 4 neutrons
- Beryllium (Be)
o 4 protons
o 4 electrons
o 5 neutrons
ATOMIC STRUCTURE KENNETH
