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Atoms and the periodic table

Atomic structure

All material things are made from atoms. There are just over one hundred different types of atom, called elements. Atoms can join together in millions of different combinations to make all the substances on Earth and beyond.

the proton and neutron are within the nucleus which is within the centre of the atom, the elctrons are on the edges of the atom

Structure of the atom

Every atom is made of a nucleus consisting of protons and neutrons. The nucleus is surrounded by electrons. Protons and electrons are oppositely charged. Neutrons have no charge. This means the nucleus of an atom is always positively charged. It is very small compared to the size of the atom.

An atom has a neutral overall charge because it has the same number of electrons as protons.

Protons and neutrons have the same mass. Electrons have such a small mass that this can usually be taken as zero.

Comparing the charge and mass of electrons, protons and neutrons

Mass110.0005 (almost zero)

The atomic number (also called the proton number) is the number of protons in an atom. All the atoms of the same element have the same number of protons – a number that is unique to that element.

The mass number (also called the nucleon number) is the total number of protons and neutrons in an atom.

The elements are arranged in the Periodic Table in ascending order of atomic number so it's easy to find the name or symbol for an atom if you know the atomic number.

Boron (5), Calcium (6), Nitrogen (7), Oxygen (8), Fluorine (9), and Neon (10)

Section of the periodic table showing elements ascending by atomic number

Most elements exist in a number of different forms or varieties called isotopes. Isotopes have the same number of protons but different numbers of neutrons, which gives them a different total mass. That means isotopes of an element have the same atomic number but different mass numbers.

Back to Atomic structure and the periodic table index

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