Node of electron density

Ap orbital has a dumbbell shape. It contains a node of electron density at the nucleus. A node means there is no electron density in this region. A p orbital is higher in energy than an s orbital (in the same shell) because its electron density is farther away from the nucleus. A p orbital is filled with electrons only after an s orbital of the same shell is full. 

The two lobes of each p orbital are opposite in phase, with a node of electron density at the nucleus. When two p orbitals combine, two molecular orbitals should form. The two p orbitals can add together constructively—that is, with like phases interacting—or destructively— that is, with opposite phases interacting. 

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

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