Chemistry (Fundamental Ideas)

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Atoms, Elements and Compounds

All substances are made up of atoms

Elements contain only one type of atom

Compounds contain more than one atom

An atom has a tiny nucleus in its centre, surrounded by electrons

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Atomic Structure

Atoms consist of protons, neutrons and electrons

Protons and electrons have equal and opposite charges. Protons are positively charged, and electrons are negatively charged

Neutrons have no electric charge. They are neutral.

Atomic number

=number of protons

(=number of electrons)

Mass number = number of protons + neutrons

Atoms are arranged in the periodic table in order of their atomic number

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The Arrangement of Electrons in Atoms

The electrons in an atom are arranged in energy levels or shells

Atoms with the number of electrons in their outermost shell belong in the same group of the periodic table

The number of electrons in the outermost shell determines how it will react.

The atoms of the unreactive noble gases (in group 0) all have very stable arrangememts of electrons

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Forming Ionic Bonds

When metals react with non-metals, charged particles called ions are formed

Metal atoms form positively charged ions

Non-metal atoms form negatively charged ions

The opposite charges strongly attract each other

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Forming Covalent Bonds

Atoms of non-metals bond to each other by sharing electrons, this is called covalent bonding

Molecules are formed

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