Ammonium (NH4+) is not an element but a polyatomic ion, which means it is a group of atoms that carry a charge. Since the periodic table only lists elements, you won’t find ammonium listed there. However, the elements that make up ammonium—nitrogen (N) and hydrogen (H)—are both on the periodic table.
Nitrogen is located in group 15 (pnictogens) and period 2, while hydrogen is in group 1 and period 1. When these elements combine, they form the ammonium ion, which is commonly found in compounds like ammonium chloride (NH4Cl) and ammonium nitrate (NH4NO3).