Molecules in this category may have three, four, five or six atoms.  The configuration is specified as AX₅ for the case with six total atoms and AX₄E for the case with five atoms, AX₃E₂ for the case with four and AX₂E₃ for the case with three.  Remeber the "E" represents electron groups that are not involved in bonding, the "X" atoms around the central atom and the "A" is the central atom.  Molecules of the type AX₅ are trigonal bipyramidal, molecules of the type AX₄E  are seesaw, molecules of the type AX₃E₂ are T-shaped, and molecules of the type AX₂E₃ are linear.