GCSE Chemistry - Atoms & Ions

What Are Atoms and Their Structure?

Introduction to Atoms

• Everything, whether living or non-living, is composed of tiny particles called atoms. A single cell can contain over 100 trillion atoms.

• Each atom consists of a central nucleus surrounded by electrons that orbit in shells. The nucleus contains protons and neutrons.

Structure of the Atom

• Protons and neutrons have a relative mass of one, while electrons are much smaller—about 2,000 times less massive.

• Protons carry a positive charge (+1), neutrons are neutral (no charge), and electrons have a negative charge (-1). This can be remembered through their names: "proton" with "positive" and "neutron" with "neutral."

Size and Composition of Atoms

• The size of an atom varies by element but generally has a radius around 0.1 nanometers. Most of an atom is empty space.

• The nucleus is significantly smaller than the entire atom—10,000 times smaller—and if drawn to scale, electrons would be too small to see.

Ions vs. Neutral Atoms

• An atom is neutral when it has equal numbers of protons and electrons; however, it can become charged (ionized) by losing or gaining electrons.

• For example, adding an electron creates a negative ion (e.g., three protons and four electrons result in a -1 charge).

Understanding the Periodic Table

• The periodic table displays different types of atoms known as elements. Each box represents an element's nuclear symbol containing vital information.

• The elemental symbol indicates the type (e.g., O for oxygen), while the atomic number shows how many protons each atom has (oxygen has eight protons).

Mass Number and Neutrons

• The mass number reflects the total count of neutrons plus protons in an atom. For instance, oxygen's mass number minus its atomic number reveals it has eight neutrons.

• Lithium serves as another example where its mass number indicates four neutrons despite having only three protons.