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SQA National 5 Chemistry The atom

The atom

This page covers the following topics:

1. Atoms, elements and compounds
2. Atom structure
3. Protons, neutrons and electrons

An atom is the smallest component of an element. An element is a substance that is made entirely of one type of atom (e.g. lithium). Elements have chemical symbols which is a one or two letter code for an element. These symbols can be found in the periodic table.

A compound is a substance made up of two or more atoms which are chemically bonded together (e.g. water, Hβ‚‚O). Compounds also have chemical formulas made up from the chemical symbols of the elements involved.

The larger number of of the two main numbers provided for an element usually is the mass number and the smaller one usually is the atomic number. For most elements the mass number is approximately twice bigger than the atomic number.

Atoms, elements and compounds

Atoms consists of electrons and a central nucleus, which is tiny compared to an atom as a whole. Electrons orbit around the nucleus in energy levels, also known as shells. The nucleus contains protons and neutrons. The nuclear radius is around 1 Γ— 10⁻¹⁴ m whilst the radius of the atom is about 1 Γ— 10⁻¹⁰ m so the nucleus is less than 1/10,000 of the size of the atom. Yet the nucleus has the majority of the mass in an atom.

Neutron is a neutral subatomic particle residing in the nucleus of an atom. Electron is a negatively charged subatomic particle residing in shells surrounding the nucleus of an atom. Proton is positively charged subatomic particle residing in the nucleus of an atom.

Atom structure

Each element has a characteristic number of protons, called the atomic number, which can be found in the periodic table. In atoms the number of electrons is the same as the number of protons. Since they have opposite charges, this ensures that every atom is neutral.

In atoms:
number of protons = atomic number
number of electrons = atomic number
number of neutrons = mass number βˆ’ atomic number

For charged ions, the number of negatively charged electrons changes. Negative ions will have a higher number of electrons since they have a negative charge that comes from the negative electrons. Thus, positive ions will have the usual number of electrons that belongs to the atoms minus their charge which indicates the number of electrons lost.

Protons, neutrons and electrons

1

Label the diagram provided with what each number represents in the periodic table.

Label the diagram provided with what each number represents in the periodic table.

2

What is the definition of compound?

What is the definition of compound?

3

The diagram provided shows the structure of a chlorine atom. Name the particles represented by crosses in the diagram.

The diagram provided shows the structure of a chlorine atom. Name the particles represented by crosses in the diagram.

4

What is an electron?

What is an electron?

5

What is a neutron?

What is a neutron?

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