Covalent Bonding

Shared Electrons Between Atoms - Types and Structures

Hello,

This post covers the concept of covalent bonding; its definition, types, and structures.  A covalent bond is formed when pairs of electrons are shared between atoms.  Covalent bonds are among the strongest forces in nature and account for the stability of water, the existence of thousands of organic compounds (carbon containing), the delocalized bonds (electrons free to roam) between metal atoms, the unique bonds between metals and non-metals within coordinate-covalent compounds, and the many forms (allotropes) of the element carbon.  Covalent bonds are either nonpolar (between identical atoms) or polar (between atoms of different elements).  Whether or not a covalent bond is polar can greatly effect the properties of a compound containing those bonds.  Properties of polar-covalent bonding will be discussed in my next post.

Types of Covalent Structures

Structures consisting of covalent bonds are molecular, polyatomic ions, metallic, or coordinate compounds.

Molecular Structures

Molecular structures are either elements in their natural state or compounds.  Most molecular elements are diatomic; meaning two atoms covalently bonded.  Exceptions are phosphorus, P4, and sulfur, S8.   The simplest molecular element is hydrogen gas: Its formation is indicated in the diagram below.

Other molecular structures are compounds.  A good example is carbon dioxide, shown below.

Compound molecular structures always consist of two or more different elements.  The fact that a carbon dioxide molecule is linear while other molecules are triangular, pyrimidal, and bent (such as water) will also be discussed in the next post.

Before we move on to polyatomic ions, we should also look at double and triple bonds.  A single bond is the sharing of one pair of electrons, therefore a double bond (the type in carbon dioxide) is the sharing of two pairs of electrons.  Likewise, a triple bond is the sharing of three pairs of electrons.  The following presentation shows more examples of molecules consisting of double (and triple) bonds.

Polyatomic Ions

A polyatomic is essentially a compound molecule with an electrical charge.  Polyatomic ions consisting of oxygen tend to exhibit resonance, which means a single ion has multiple electron arrangements.  This has the effect of stabilizing the ion.  The next graphic displays the resonance structures of the nitrite ion.

A couple notes about the diagram: The "minus" signs are there to indicate a negative-one charge on the two oxygen atoms indicated.  The double arrow indicates that we have a single nitrite ion existing in two forms.

Coordination Compounds

A coordination compound consists of a central metal atom surrounded by nonmetal atoms called ligands.  The ligands provide all of the bonding electrons, which then occupy empty d-Orbitals of the central metal atom.  The crystal-field theory describes coordination compound structures in terms of "perturbations" between the electrical fields of ligands and the internal electrical fields of the central metal atom.

Metal-Metal Bonding

Covalent bonding within metals involves an overlap of d-orbitals between bonded metal atoms.  This allows electrons to roam across the entire metal structure.  The phrase, delocalized-electrons, is used to describe the resulting "sea of electrons".  It is exactly this freedom of electron motion which makes metals excellent conductors of heat and electricity!

That's all for this post.  Have a good one!

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