ENERGY-LEVEL DIAGRAMS DESCRIBE HOW ORBITALS ARE OCCUPIED

Two electrons having opposite spins may pair together in an atomic orbital. 

This energy-level diagram shows the relative energy levels of atomic orbitals in a multielectron atom (in this case rubidium, Rb, atomic number 37). 

A boron atom, B (atomic number 5), in its lowest energy state has four of its five electrons filling the Is and 2s orbitals. Its fifth electron may reside in any one of the 2p orbitals, all of which are at the same energy level  

A carbon atom, C (atomic number 6), has six electrons. Five of them occupy the Is, 2s, and 2p orbitals just as the electrons in boron do. Carbon s sixth electron, however, has a choice of either pairing up with the fifth electron in the same 2p orbital or entering a 2p orbital of its own  

Because electrons have a natural repulsion for one another, they do not begin to pair up in the same orbital until all the other orbitals at the same energy level are singly occupied. Electrons in separate orbitals tend to spin in the same direction, and so the arrows should be shown all pointing in the same direction until pairing is necessary. For these reasons, the two 2p electrons of a carbon atom in its lowest energy state are in separate 2p orbitals and are drawn pointing in the same direction  

This energy-level diagram show.s the relative energy levels of High energy (far from nucleus) 00 

There is no pairing of 2p electrons in the nitrogen atom, N (atomic number 7), which has seven electrons. The oxygen atom, O (atomic number 8), however, lias eight elearons, two of which are forced to pair up in one 2p orbital (it doesn t matter which one). 

---

Energy-Level Diagrams Describe How Orbitals Are Occupied... 

ENERGY LEVEL DIAGRAMS DESCRIBE HOW ORBITALS ARE OCCUPIED... 

The electron s wave function (iK atomic orbital) is a mathematical description of the electron s wavelike behavior in an atom. Each wave function is associated with one of the atom s allowed energy states. The probability density of finding the electron at a particular location is represented by An electron density diagram and a radial probability distribution plot show how the electron occupies the space near the nucleus for a particular energy level. Three features of an atomic orbital are described by quantum numbers size (n), shape (/), and orientation (m/). Orbitals with the same n and / values constitute a sublevel sublevels with the same n value constitute an energy level. A sublevel with / = 0 has a spherical (s) orbital a sublevel with / = 1 has three, two-lobed (p) orbitals and a sublevel with / = 2 has five, multi-lobed (d) orbitals. In the special case of the H atom, the energy levels depend on the n value only. 

---