Also the size of the central atom has some effect on bond angles, like you noticed.

They reported the measured bond angle to be 103 degrees, with O the central atom.

It has a tetrahedral configuration, with lead as the central atom.

The central atom is sp2 hybridized with one lone pair.

This process can be repeated until only one bond remains to the molecule's central atom.

The central atoms must be identified, i.e. by assigning numbers to them.

Then attach four different colored balls (one each) to the central atom.

Inside the bracket the symbol of the central atom is placed first.

Therefore, the central atom is predicted to adopt a linear geometry.

The A represents the central atom and always has an implied subscript one.