Atomic Structure:Electron Configuration The lowest-energy arrangement is known as the ground-state electron configuration ■ We can predict this arrangement by the following rules: 1.Lowest-energy orbitals fill first:1s->2s->2p →3s→3p→4s→3d(Aufbau principle) 2.Electron spin can have only two orientations, up T and down.Only two electrons can occupy an orbital,and they must be of opposite spin (Pauli exclusion principle) 3.If two or more empty orbitals of equal energy are available,electrons occupy each with spins parallel until all orbitals have one electron (Hund's rule)
Atomic Structure: Electron Configuration The lowest-energy arrangement is known as the ground-state electron configuration We can predict this arrangement by the following rules: 1. Lowest-energy orbitals fill first: 1 s → 2 s → 2 p → 3 s → 3 p → 4 s → 3 d (Aufbau principle) 2. Electron spin can have only two orientations, up ↑ and down ↓. Only two electrons can occupy an orbital, and they must be of opposite spin (Pauli exclusion principle ) 3. If two or more empty orbitals of equal energy are available, electrons occupy each with spins parallel until all orbitals have one electron (Hund's rule)
TABLE 1.1 Ground-State Electron Configurations of Some Elements Atomic Atomic Element number Configuration Element number Configuration Hydrogen 1s Lithium 3 28 2p + + 2pH H H Carbon 6 2s Neon 10 1s H 1s 州 3s + 即 H H H Sodium 11 2p H H Argon 18 1s 4 HHH HH 1s 2004 Thomson-Brooks/Cole