There are some usual rules that can apply. Looking at a periodic table, group one is on the far left with hydrogen at the top working down to lithium, sodium (Na) potassium (K), etc. These always have a 1+ charge on them. Group 2, Beryllium, (Be), magnesium (Mg), calcium (Ca), etc. Always has a 2+ charge on them. Skip over to the right side. Group 8, Helium (He), neon (Ne), etc. Are noble gases and are neutral with no charge. Next to them are group 7, florine (F), chlorine (Cl), etc. Usually have a 1- charge. Group 6 oxygen (O), sulfur (S), etc. Usually have a 2- charge. Groups 3, 4, and 5 are kind of up in the air. Silver (Ag) always has a 1+ charge, zinc (Zn) a 2+, and aluminum (Al) a 3+ charge. Many of the transition metals, groups 3B-2B can change charges. Other than that, you have to look to what they are paired with to determine their charge.Ions are a whole new story.
