In general, the number of valence electrons for an atom can be determined by looking at its group number on the periodic table. For example, an atom in group 1A will have 1 valence electron, an atom in group 2A will have 2 valence electrons, and so on.
Lewis structures are used to represent the valence electron arrangement in molecules and ions. They help us visualize how atoms are bonded to each other and determine the overall shape and polarity of a molecule.
In most cases, the central atom in a Lewis structure is the atom with the lowest electronegativity. This is because the central atom is usually the least likely to attract electrons from other atoms.
Yes, atoms in the third row of the periodic table and beyond can have more than 8 valence electrons in a Lewis structure. This is known as expanded octet and is commonly seen in molecules containing atoms such as sulfur, phosphorus, and chlorine.
The formal charge of an atom in a Lewis structure is calculated by subtracting the number of lone pair electrons and half the number of shared electrons from the number of valence electrons for that atom. The formal charges of all atoms in a molecule should add up to the overall charge of the molecule.