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Atom
The smallest particle of an element that retains the identity of the element.
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Electron
A negatively charged particle within the atom.
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Subatomic particle
A particle that is smaller than an atom.
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Nucleus
The positively charged centre of an atom.
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Proton
A positively charged particle that is part of every atomic nucleus.
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Neutron
An uncharged particle that is part of almost every atomic nucleus.
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Energy levels
Areas of space surrounding the nucleus of an atom that electrons occupy.
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Atomic Number
The number of protons in the nucleus of an atom.
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Mass Number
The sum of the number of protons and the number of neutrons in the nucleus of an atom.
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Isotope
One of two or more forms of an element that have the same number of protons but a different number of neutrons.
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Atomic Mass
The average mass of the naturally occurring isotopes of an atom.
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Periodic Table
A system for organizing the elements into columns and rows, so that elements with similar properties are in the same column.
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Metal
An element that is hard, shiny, malleable, and ductile, and is a good conductor of heat and electricity.
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Non-metal
An element that is not shiny, malleable, ductile, and is a poor conductor of heat and electricity.
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Metalloid
An element that shares its some properties with metal and some properties with non-metals.
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Period
A horizontal row of elements in the periodic table.
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Group
A vertical column of elements in the periodic table.
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Alkali metals
Found in Group 1. They have low melting points and are highly reactive.
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Alkaline-Earth metals
Found in Group 2. They are also highly reactive, but less so than Alkali metals. They are often used in fireworks since they produce colourful flames.
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Halogens
Found in group 17. These non-metals are highly reactive and extremely corrosive.
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Noble gases
Found in group 18. These non-metals are all odourless, colourless gases at room temperature. However, they are non-reactive.
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Valence electrons
An electron in the outermost occupied energy level of an atom.
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