Question

If an atom contains 12 positive particles it must also contain 12 negative particles, rIght?

Answer 1

Well not always, these positive particles are called protons, and the negative particles are called electrons. Protons dictate an elements identity Hydrogen has 1 proton, Helium has 2 protons etc.

The number of electrons can be varied for an atom to be
neutral number of electrons = number of protons

But electrons can be removed from the particle by various ways changing its charge to + or electrons may be gained by that atom changing its charge to -

For example,

NaCl

Sodium gives 1 electron to Chlorine

so sodium exists with a positive charge 11 protons 10 electrons and chlorine has a negative charge 17 protons 18 electrons

Answer 2

That is an example of an ionic bond

Answer 3

But that is going far beyond the scope of this question

Answer 4

if it's called an "atom", then the implication is yes, it is a neutral particle, and so must have equal numbers of positive and negative particles (protons & electrons)