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Atoms

Atoms are the smallest part of an element.

They are made up of subatomic particles. The main three being protons, neutrons and electrons.

protons - p+, charge 1+, mass 1 amu, found in the nucleus

Neutrons - N0, charge O, mass 1 amu, found in the nucleus

Electrons - E-, Charge 1-, mass 0.0005, found outside the nucleus

An atom contains and equal amount of protons and electrons.

Atomic Number - Number of protons

Atomic Mass - The sum of the protons plus neutrons.

To find the number of neutrons: Mass number - Atomic Number.

Electron Representation

1s_ 2s_ 2p_ _ _ 3s_ 3p_ _ _ 4s_ 3d_ _ _ _ _4p_ _ _ 5s_ 4d_ _ _ _ _ 5p_ _ _

Electrons furthest away from the nucleus can be gained, lost or shared. Electrons in the outermost energy level are called valance electrons.

Isotopes and Ions

If an element has varying numbers of neutrons, these atoms are then known as isotopes.

Atoms which have unequal numbers or protons and electrons are known as ions.e.g sodium (NA), atomic number 11, is neutral.It has 1 electron on its own spinning in the outer orbital so will give away this electron to make itself stable where possible.

Sodium Ions are represented as Na+ (It has lost one electron) and now contains more positive charges than negative charges. Magnesium Ion is represented as MG2+ as it has lost two electrons.

Electrons which have a positive charge are called Cathions.

Chlorine has 7 electrons in its valence shell, it needs one moer to become stable. By gaining another electron, it has turned negative (more electrons than protons). It is now repesented as Cl-.

Electrons which have a negative charge are called anions.

Ions are commonly found in salt compounds. When salts are dissolved in water they produce solutions which conduct electricity. These substances are known as electrolytes.

If a substance is an electrolyte, the compound is probably ionically bonded. If its a nonelectrolyte, probably covalently bonded.

Ionic Bonds - Where two or more elements transfer electrons.

Covalent Bonds - Where two or more elements share electrons. e.g H2O