atoms are made of protons, electrons and neutrons
atomic number of element is the number of protons. Atomic number is characteristic for that element
therefore by knowing the number of protons we know the atomic number, therefore we can use the periodic table to identify what the element is
element with atomic number 12 is - Mg
Atoms of elements are neutral in their ground state with equal number of protons and neutrons
Mg has 12 protons and 12 electrons
once atoms lose or gain electrons they are called ions
here Mg has only 10 electrons which means it has lost 2 electrons. then the net charge of Mg becomes
12 positive charges + 10 negative charges = 2 positive
Mg has a net charge of 2 and since its positively charged its called a cation
the ion with 12 protons and 10 electrons is Mg²⁺