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Positive ions are called cations, and negative ions are called anions.

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Ions are electrically charged particles, and they form due to the difference in the number of electrons.

When the number of electrons and protons is equal, since their electrical charge is equal(+1 for a proton and -1 for an electron), they cancel out.

However, if there are more electrons in the atom, then the atom will be an anion, as there is more negative charge.

$$ ion's\; charge=\#of\;protons - \#of\;electrons $$

All the electrons in the outer shell are called valence electrons. Every other electron is called a core electron.