If the symbol X represents a central atom, Y represents outer atoms, and Z represents lone pairs on the central atom, the structure The central X atom is single bonded to two Y atoms, which are 180 degrees apart. The X atom has two lone pairs. could be abbreviated as XY2Z2. Classify each molecule according to its shape. If the symbol X represents a central atom, Y represents outer atoms, and Z represents lone pairs on the central atom, the structure The central X atom is single bonded to two Y atoms, which are 180 degrees apart. The X atom has two lone pairs. could be abbreviated as XY2Z2. Classify each molecule according to its shape.