Ions, Isotops, and Electonic struckture

science

Subatomic particles located inside the atomic nucleus

Protons and neutrons

Maximum electron capacities for the first three shells (up to element 20)

$2$ in the 1st shell, $8$ in the 2nd shell, and $8$ in the 3rd shell

Valence electrons

Electrons in the outermost shell of an atom that determine its chemical reactivity

Ion

An atom that has gained or lost electrons, giving it a net electrical charge

Type of ion formed when an atom loses electrons

Positive ion (because it has more protons than electrons)

Type of ion formed when an atom gains electrons

Negative ion (because it has more electrons than protons)

Primary reason atoms form ions

To obtain a full outer electron shell and achieve greater stability

Isotopes

Atoms of the same element that have the same number of protons but a different number of neutrons

Atomic number

The number of protons in the nucleus of an atom

Mass number

The total number of protons plus neutrons in an atom's nucleus

Formula to calculate the number of neutrons in an atom

$$\text{Neutrons} = \text{Mass number} - \text{Atomic number}$$

Subatomic particle responsible for identifying the element

Proton