Chemistry

• Nucleus = protons (positive) + neutrons (no charge)

• Nucleus surrounded by electrons (negative). Atom has no overall charge.

• Isotopes = atoms of the same element with different number of neutrons.

• Atomic number = number of protons and neutrons in an atom.

• Atoms arranged in periodic table in groups and periods.

Alkali metals = 1 electron in the outer shell.

Halogens = 7 electrons in the outer shell.

When atoms form chemical bonds, their outer shell of electrons changes.

Key words - atomic number, proton, neutron, electron, alkali, isotopes, chemical bonds.

• Ionic compounds = giant structures held together by strong forces of attraction between oppositely charged ions.

• Ionic bonds ------> metal and no-metal atoms ------> electrons are transferred

• Covalent bonds ------> non-metal atoms ------> electrons are shared

Giant covalent structures = strong, covalent bonds and high melting points, e.g. diamond, graphite, silicon dioxide.

Note...

Metals can conduct heat and electricity because they have delocalised electrons.

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Compound = two or more elements chemically bonded together.

Mixture = two or more elements or compounds not chemically bonded together.