Atoms, Ions, & IsotopesOh, My!Part III

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Outer Structure of an AtomOuter Structure of an Atom

• The electron cloud contains several energy levels

Electrons - negatively (-) charged particles located in specific energy levels surrounding the nucleus

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Outer Structure of an AtomOuter Structure of an Atom• Multiple energy levels in the electron cloud

completely surround the nucleus.Electrons follow a specific order to fill the energy

levels.

Maximum of 2

electrons

Nucleus

Maximum of 8

electrons Maximum of 8

electrons*

*Applies to the first 18 elements only

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Valence Electrons•Electrons found on the last/outermost energy level

•The number of valence electrons determines reactivity of the atom

•Full outer shell-Nonreactive•As you get closer to a full shell the less reactive an atoms is

–Atoms can achieve a full shell by losing or gaining electrons

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This is the order the electrons fill up the energy levels/shells/orbitals.

You do not go to the next energy level until the one you are on is full.

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Charge of an Atom•Most atoms are NEUTRAL (no charge)

The number of Protons = number of Electrons

•If an atom loses or gains electrons then it will have a charge

#p > #e; positive charge#p < #e; negative charge

•The valence electrons are the electrons being lost or gained.

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Cation•Positively charged ions•#p > #e•Lost of electron(s)

IonsAn atom that has gained or lost electrons

In the example, sodium is a neutral atom when it has 11 protons and 11 electrons.

When it loses its one valence electron, it has 11 protons and 10 electrons, which makes it have a +1 charge.

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• Negatively charged ions• #p < #e• Gain electron(s)

Anion

In the example, chlorine is a neutral atom when it has 17 protons and 17 electrons.

When it gains one electron, it has 17 protons and 18 electrons, which makes it have a -1 charge.