Atomic Structure Electron Configurations

The lowest-energy arrangement or ground-state electron configuration, of an atom is a listing of the orbitals occupied by its electrons. We can predict this arrangement by following three rules. 

Rule 1 The lowest-energy orbitals fill up first, according to the order Is 2s 2p 

3s 3p — 4s — 3d, a statement called the aiifbau principle. Note that the 4s orbital lies between the 3p and 3d orbitals in energy. 

Rule 2 Electrons act as if they were spinning around an axis, in much the same way that the earth spins. This spin can have two orientations, denoted as up T and clow n i. Only two electrons can occupy an orbital, and they must be of opposite spin, a statement called the Pauli exclusion principle. 

Rule 3 If two or more empty orbitals of equal energy are available, one electron occupies each with spins parallel until all orbitals are half-full, a statement called Hand s rule. 

Sonic examples of how these rules apply are showai in Table l.l. Hydrogen, for instance, has only one electron, which must occupy the lovvest-energ - orbital. Thus, hydrogen has a l.s ground-state configuration. Carbon has six electrons and the ground-state configuration Is 2s 2p. nd so forth. Note that a super-script is UbCd tn represent the number of electrons in a jiarticular orbital. 

---

PERIODIC LAW. Originally stated in recognition of an empirical periodic variation of physical and chemical properties of the elements with atomic weight, this law is now understood to he based fundamentally on atomic number and atomic structure. A modern statement is the electronic configurations of the atoms of the elements vary periodically with their atomic number. Consequently, all properties of the elements that depend on their atomic structure (electronic configuration) tend also to change with increasing atomic number in a periodic manner. 

Atomic Structure The Nucleus Atomic Structure Orbitals 4 Atomic Structure Electron Configurations 6 Development of Chemical Bonding Theory 7 The Nature of Chemical Bonds Valence Bond Theory sp Hybrid Orbitals and the Structure of Methane 12 sp Hybrid Orbitals and the Structure of Ethane 13 sp2 Hybrid Orbitals and the Structure of Ethylene 14 sp Hybrid Orbitals and the Structure of Acetylene 17 Hybridization of Nitrogen, Oxygen, Phosphorus, and Sulfur 18 The Nature of Chemical Bonds Molecular Orbital Theory 20 Drawing Chemical Structures 21 Summary 24... 

Some of the important properties of solid materials depend on geometrie atomie arrangements and also the interactions that exist among constituent atoms or molecules. This chapter, by way of preparation for subsequent discussions, considers several fundamental and important concepts—namely, atomic structure, electron configurations in atoms and the periodic table, and the various types of primary and secondary interatomic bonds that hold together the atoms that compose a solid. These topics are reviewed briefly, under the assumption that some of the material is familiar to the reader. 

---