Standard Grade Chemistry - Atoms & Periodic Table

Topic 3 revision notes.

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Periodic Table

The Periodic Table is how scientists classify elements.
A column of elements in the periodic table is called a group.
Elements in the same group have similar chemical properties.

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Important Groups

Group 1:- alkali metals(very reactive)
Group 7:- halogens(very reactive)
Group 0:- noble gases(very unreactive)

The transition metals are an important block of elements between groups 2 and 3.
Most elements are solid, a few are gases and two bromine and mercury are liquids.
Most of the solid elements are also metals.

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Every element is made from small particles called atoms.
Atoms of different elements are different each having a specific number of protons, the number of protons is known as the Atomic Number.

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Atomic Structure

All atoms have a small positively charged central nucleus.
Negatively charged electrons move around outside the nucleus in orbitals called shells.
All atoms are electrically neutral because the number of positive protons equals the number of negative electrons
The electrons are in their shells , these electron arrangements can be found in the data book.
Elements with the same number of outer electrons have similar chemical properties.

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Protons, Nuetrons And Electrons

The nucleus of any atom is positively charged because of the protons.
The atoms of different elements have different numbers of protons.
All atoms except for hydrogen have neutrons in their nucleus.
The number of protons in any element is fixed.
The number of neutrons in any element can vary.
Atoms with the same number of protons yet different numbers of neutrons are called Isotopes.
The Atomic Number of an element is equal to the number of protons in the nucleus. This will also equal the number of electrons in a neutral atom.
The Mass Number of an atom is equal to the number of protons plus the number of neutron in the nucleus.
Isotopes will have the same atomic number and different mass numbers.
For any isotope a special symbol can be written. (nuclide notation)

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Relative Atomic Mass

The relative atomic mass of an element is the average mass of one atom taking account of each isotope and the abundance of each isotope, because of this the relative atomic mass is rarely a whole number.

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Ions are formed from atoms which have lost or gained electrons. Metal atoms lose electrons to form ions, non-metallic atoms gain electrons to form ions. They are chemically charged atoms.

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