AQA GCSE FOUNDATION PHYSICS - Atomic Number, Mass Number, and Isotopes

Atomic Number, Mass Number, and Isotopes: A Foundation Physics Tutorial

1. The Atom: A Tiny World

Everything around us is made of tiny particles called atoms. Atoms are so small that you can't even see them with a microscope!

2. Atomic Number: Identifying Atoms

Each element has a unique atomic number. This number tells you how many protons are in the nucleus of an atom. Protons are positively charged particles found in the atom's center.

• Example: The atomic number of carbon is 6. This means every carbon atom has 6 protons in its nucleus.

3. Mass Number: The Weight of an Atom

The mass number tells you the total number of protons and neutrons in an atom's nucleus. * Neutrons are neutral particles also found in the nucleus.

• Example: A carbon atom with a mass number of 12 has 6 protons and 6 neutrons (12 - 6 = 6).

4. Isotopes: Variations of the Same Element

Atoms of the same element can have different numbers of neutrons. These variations are called isotopes.

• Key Point: Isotopes of an element have the same atomic number but different mass numbers.

• Example: Carbon-12 and Carbon-14 are both isotopes of carbon. Both have 6 protons, but Carbon-12 has 6 neutrons, while Carbon-14 has 8 neutrons.

5. Representing Atoms and Isotopes

We use a special notation to represent atoms and isotopes:

  X
 A
 Z

• X: The element symbol (e.g., C for carbon)
• Z: The atomic number (number of protons)
• A: The mass number (number of protons + neutrons)

Examples:

• Carbon-12:
  12 C 6
• Carbon-14: 14 C 6

6. Understanding Isotopes

• Stability: Some isotopes are more stable than others. For example, Carbon-14 is radioactive, meaning it decays over time, while Carbon-12 is stable.

• Applications: Isotopes have various uses, from dating ancient artifacts to medical imaging.

7. Key Takeaways

• Atomic number defines an element.
• Mass number tells you the total number of protons and neutrons in an atom.
• Isotopes are variations of the same element with different numbers of neutrons.
• The notation A X Z helps us represent atoms and isotopes.