Covalent and Metallic Bonding

Science, Grade 6


Table Of Contents: Covalent and Metallic Bonding

1. Covalent Bonds
Covalent bonding is a type of chemical bonding that occurs between two non-metallic atoms. It is characterized by the sharing of one or more pairs of electrons between atoms. By sharing electrons, two atoms can mutually complete their valence shells to become more stable. For example, since each chlorine atom has 7 electrons in its outer shell, two chlorine atoms will each share an electron to obtain a complete outer shell and form a stable Cl₂ molecule. For every pair of electrons shared between two atoms, a single covalent bond is formed. Atoms can also share two or three pairs of electrons and are named accordingly as double and triple bonds. A single line indicates a bond between two atoms, double lines indicate a double bond and triple lines represent a triple bond.
2. Nonpolar and Polar Covalent Bonding
There are two types of covalent bonding - nonpolar and polar. Nonpolar bonding results when two identical non-metals equally share electrons between them. Diatomic molecules such as O₂ or I₂ form nonpolar covalent bonds where both atoms share the electrons equally. Polar bonding results when two different non-metals unequally share electrons between them. Compounds such as carbon dioxide, ammonia, and water have polar covalent bonds. Certain other compounds, such as ethane (C₂H₆), have both polar and nonpolar bonds. Ethane, has polar bonds between the carbon and hydrogen, and nonpolar bonds between the two carbon atoms.
3. Covalent Compounds
The atoms in covalent compounds, also known as molecular compounds, are bonded together by covalent bonds. Unlike ionic compounds which form a regular pattern, covalent compounds form individual molecules that are not connected to each other. Due to weak intermolecular forces, most covalent molecules or covalent compounds are liquids or gases at room temperature, with low melting and boiling points. And since covalent molecules do not separate into ions when dissolved in water, they are poor conductors of electricity. Although most covalent compounds are gases or liquids at room temperature, there's a class of solid compounds known as covalent network solids that are bonded by covalent bonds, but in a lattice structure. Such compounds are typically hard, transparent, and have high melting points. Examples include diamond, quartz and graphite, among others.
4. Covalent Formulas and Names of Covalent Compounds
The formula for a covalent compound can be derived from its name by writing the symbols for the first and second element and translating the prefixes into subscripts. For example, sulfur trioxide would be written as SO₃. Covalent compounds are named in a similar manner to binary ionic compounds. (Binary compounds are compounds made up of only two elements). To name binary covalent compounds apply the following rules: 1) Name the first nonmetal using the element's full name. 2) Name the second nonmetal element with an "-ide" ending as if it were an anion. 3) Indicate the number of atoms present (its subscript) of each element with the prefixes, "mono-", "di-", "tri-" and so on. For example, the formula name for CCl₄, with one carbon, and four chlorine atoms is carbon tetrachloride.
5. Metallic Bonding
The force that holds atoms together in a metallic substance is a metallic bond. A metallic substance consists of closely packed atoms, arranged in a very compact and orderly pattern. The valence shells (outermost electron shell) of the metal atoms overlap with many of the neighboring atoms. As a result, instead of orbiting their atoms, the valence electrons leave individual atoms and continually move throughout the metal structure from one atom to another. The atoms that the electrons leave behind become positive ions, and the interaction between such ions and valence electrons provides the binding force that holds a metallic structure together. This free movement of the valence electrons also provides metals a number of their unique characteristics, such as strength, malleability, ductility, thermal and electrical conductivity, opacity and luster.