Changes

Atoms are comprised of three subatomic particles: positively charged [[proton|protons]], electrically neutral [[neutron|neutrons]] and negatively charged [[electron|electrons]]. Protons and neutrons are comprised of quarks and are contained in close proximity in the center of an atom, forming the [[nucleus]]. Electrons inhabit the space around the nucleus, and are arranged around it in a series of layers, known as [[electron shell|shells]] or energy levels.

Atoms are comprised of three subatomic particles: positively charged [[proton|protons]], electrically neutral [[neutron|neutrons]] and negatively charged [[electron|electrons]]. Protons and neutrons are comprised of quarks and are contained in close proximity in the center of an atom, forming the [[nucleus]]. Electrons inhabit the space around the nucleus, and are arranged around it in a series of layers, known as [[electron shell|shells]] or energy levels.

Currently quarks and electrons are considered truly elementary particles.

Currently quarks and electrons are considered truly elementary particles, though neither has ever been seen.

===Atomic Number===

===Atomic Number===