In groups on the periodic table, how do you know the charges of the elements in that group?
Group 1 elements (alkali metals such as Li, Na, K...) all have one valence electron that they donate when forming ionic bonds. This will cause them to have a charge of +1.T he alkaline earth metals (Ca, Mg) have two valence electrons they donate which means their charge when forming ions is +2. The members of the aluminum family lose three electrons giving them a charge of +3.
The halogens (Cl, F, Br) all have 7 valence electrons and will gain one electron. This means they have a -1 charge. The oxygen family elements have 6 valence electrons. They gain two electrons and have a -2 charge. The nitrogen family elements gain 3 electrons, so their charge is -3.
Members of the carbon family sometimes gain 4 electrons (-4 charge) but in other situations may lose 4 electrons (+4 charge).
Transition metals (d block of the periodic table) often have more than one oxidation state.
These videos provide further discussion of this topic.