Diatomic molecules covalent bonds

Example For solid Zn, 274 pm between nuclei, so r (atomic radius) = 137 pm For nometallic elements, r is determined for diatomic molecules (covalent bond). 

For nometallic elements, r is determined for diatomic molecules (covalent bond). 

For a homonuclear diatomic molecule, the bond is purely covalent (a, = 0, ac = 1) whereas fora heteronudear diatomic molecule the bond shows mixed covalent-ionic character (a 0, ac 0). In the limit as the separation between the atomic energy levels on the two atoms becomes very large the bond becomes purely ionic (at = 1, ac = 0). 

The electronic structure of the chlorine atom (3s-3p ) provides a satisfactory explanation of the elemental form of this substance also. The single half-filled 3p orbital can be used to form one covalent bond, and therefore chlorine exists as a diatomic molecule. Finally, in the argon atom all valence orbitals of low energy are occupied by electrons, and the possibility for chemical bonding between the atoms is lost. 

The charges on the atoms in HCI are called partial charges. We show the partial charges on the atoms by writing 8+l I—Cl8. A bond in which ionic contributions to the resonance result in partial charges is called a polar covalent bond. All bonds between atoms of different elements are polar to some extent. The bonds in homonuclear (same element) diatomic molecules and ions are nonpolar. 

In Section 2.12, we saw that a polar covalent bond in which electrons are not evenly distributed has a nonzero dipole moment. A polar molecule is a molecule with a nonzero dipole moment. All diatomic molecules are polar if their bonds are polar. An HC1 molecule, with its polar covalent bond (8+H—Clfi ), is a polar molecule. Its dipole moment of 1.1 D is typical of polar diatomic molecules (Table 3.1). All diatomic molecules that are composed of atoms of different elements are at least slightly polar. A nonpolar molecule is a molecule that has no electric dipole moment. All homonuclear diatomic molecules, diatomic molecules containing atoms of only one element, such as 02, N2, and Cl2, are nonpolar, because their bonds are nonpolar. 

The halogens, the elements from Group 17 of the periodic table, provide an introduction to intermolecular forces. These elements exist as diatomic molecules F2, CI2, Bf2, and I2. The bonding patterns of the four halogens are identical. Each molecule contains two atoms held together by a single covalent bond that can be described by end-on overlap of valence p orbitals. 

It is important to point out that almost all bonds are polar bonds, whether they are approximately described as covalent or ionic. The bonds in the molecules of the various forms of the elements such as the diatomic molecules H2, CI2, and N2, larger molecules such as P4 and Sg, and infinite molecules such as diamond may be described as pure covalent bonds... 

Atoms do not all have the same ability to attract electrons. When two different types of atoms form a covalent bond by sharing a pair of electrons, the shared pair of electrons will spend more time in the vicinity of the atom that has the greater ability to attract them. In other words, the electron pair is shared, but it is not shared equally. The ability of an atom in a molecule to attract electrons to it is expressed as the electronegativity of the atom. Earlier, for a homonuclear diatomic molecule we wrote the combination of two atomic wave functions as... 

An HC1 molecule is a heteronuclear diatomic molecule composed of H (EN = 2.1) and Cl (EN = 3.0). Because the electronegativities of the elements are different, the pull on the electrons in the covalent bond between them is unequal. Hence HC1 is a polar molecule. 

---