Dalton's atomic model  

In a nutshell

Everything in the universe is made up of atoms. An atom consists of subatomic particles called neutrons, protons and electrons. In this summary you will learn about the structure of an atom, the key ideas in Dalton's atomic model and the properties of subatomic particles.  

Definitions

Dalton's atomic theory 

John Dalton published his atomic theory which consists of four key ideas.

• Everything is made up of very small particles called atoms. 
• Atoms are indivisible; they cannot be broken down into simpler particles. 
• Atoms cannot be created or destroyed.
• Atoms of the same element are identical and will therefore have the same size and mass. 

Example

All sodium atoms are identical.

Atoms of different elements will have different masses and sizes.

Example 

A carbon atom will have a different mass and size to a sodium atom.

Compounds are produced by combining two or more different types of atoms. A chemical reaction is needed to rearrange atoms in the reactants in order to produce a product compound.

Structure of an atom

An atom is made up of three sub-atomic particles: neutrons, protons and electrons. Neutrons and protons are found in the nucleus of an atom. Surrounding the nucleus are shells filled with electrons.

1. Nucleus 2. Electrons 3. Shells 4. Protons 5. Neutrons

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Masses of sub-atomic particles 

Subatomic particles have incredibly small masses which are difficult to work with, therefore instead of using their real masses we use relative masses.

Protons and neutrons have the same mass, they have a relative mass of 1. Electrons are considerably smaller than protons and neutrons (around $$2000\times$$​ smaller) and their mass is often ignored.

The nucleus contains nearly all the atoms mass given that this is where the protons and neutrons are. The size of the nucleus is significantly smaller than the size of the overall atom.

Charges of sub-atomic particles

Neutrons have no charge; they are neutral. Protons and electrons have opposite charges, protons are positively charged and electrons are negatively charged.

Properties of subatomic particles

The table below shows the relative masses, charges and positions of neutrons, protons and electrons.

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