An atom is a neutral particle.

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Atoms have the equal number of positive proton to negative electrons.​

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Atoms are​ identified based on the number of protons they contain.

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Atoms of the same element have the same number of protons

Atoms

Isotopes are atoms of the same element that have the same number of protons but different number of neutrons.

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​They therefore have the same atomic number but different mass number.

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Most elements exist as isotopes.​ Usually written as symbol-mass # Ex. C-12

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Look for similar proton number to identfy isotopes

ISOTOPES

All have atomic number of 1.

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Each have a different mass number

Hydrogen Isotopes

All have atomic number of 3.

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Each have a different mass number

Lithium Isotopes

The Isotopes are determined by the number of Neutrons they contain.

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One of the isotopes will be more common than the others.

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The atomic masses in the Periodic table is an average mass based on the Percent of each in nature.

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Ex. H-1 is the most common​. The mass of H is periodic table is closer to 1.

With isotopes:

All atoms want to have a 'full' valence (outer) shell to be stable.

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To get this, they either lose or gain electrons and so are no longer neutral. They are charged.

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An ion is a charged atom that has an unequal number of protons and electrons.​

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The charge depends on if they gained or lost electrons

IONS

When atoms lose electrons they now have more positively charged Protons in their nucleus than negatively charged electrons.

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They therefore have excess positive charge and so become positive. Charge based on how many more protons than electrons they have.

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Cations are positively charged ions.​

Cations

When atoms gain electrons they now have more than negatively charged electrons than positively charged Protons in their nucleus .

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They therefore have excess negative charge and so become negative. Charge based on how many more electrons than protons they have.

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Anions are negatively charged ions.​

Anions

Examples:

Fluorine (F) has 7 valence electrons. It gains 1 electron to be form F^- ion.

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​Oxygen (O) has 6 valence electons and so gains 2 electrons to form O^2- ion.

​ANION

Sodium (Na) has 1 valence electron. It loses 1 electron and so forms ion Na⁺

Calcium (Ca) has 2 valence elctrons. It loses 2 electrons t form ion Ca²⁺​

CATION