First let’s look at the basics!
It’s important to remember that atoms have equal amounts of protons and electrons.
〜 Protons
Protons are subatomic particles that have a positive charge ( + )
〜 Electrons
Electrons are subatomic particles that have a negative charge ( - )
〜 Neutrons
Neutrons are electrically neutral (have no charge) subatomic particles.
〜 Ions
An ion of an atom is essentially when an atom gains or loses and electron to become electrically stable (have a full valence shell).
— Not sure what a valence shell is?
A valence shell of an atom is the outermost shell of an atom’s electron structure. A full valence shell is when the last shell (the outermost/valence shell) has 8 electrons.
There are two types of ions: a cation and an anion.
「 Cation 」
A cation is a positively charged ion, meaning the atom has LOST an electron/(s) and therefore has more protons than electrons (because remember, they start off with equal amounts!)
「 Anion 」
An anion is a negatively charged ion, meaning that the atom has GAINES an electron/(s) and therefore has more electrons than protons.
[ ! ] It is important to keep in mind that either way, the number of protons does NOT change!
To answer your question, if an ion has a negative charge, it means that its atom has gained an electron!
Hope this helps! :)