3. Why are protons so important?

Protons determine the chemical identity of an atom because they are permanently anchored in the nucleus, where their attraction determines how many electrons the atom can hold. By contrast, electrons come and go, and their numbers vary. Despite very different chemical behavior, the atom and the ion shown below are both lithium because they have three protons in the nucleus.

Lithium(Li)

3 protons

3 electrons

Lithium(Li+)

3 protons

2 electrons

A Lithium atom (Li) and a Lithium ion (Li superscript plus) are depicted one next to the other. The lithium atom is represented by 2 concentric circles of different sizes with the smaller circle having a dark purple color and the larger circle (annulus) having a light purple color. At the center of the circles, 3 red (3 protons) and 4 light brown spheres (4 neutrons) are clumped together forming the nucleus. 2 yellow spheres with minus signs representing 2 electrons are on the circumference of the first concentric circle. 1 electron is on the circumference of second concentric circle. The lithium ion is represented by a circle having a dark purple color. At the center of the circle, 4 neutrons and 3 protons are clumped together forming the nucleus. 2 electrons are on the circumference of the circle.