Overview:
Many chemical compounds are not formed by ionic bonds, but by covalent bonds, where a number of elements share the same electrons. Compounds that are formed by covalent bonds are not limited to elements that can transfer electrons between one another. Some bonds are double or even triple.
How Is Covalent Bonding like Ionic Bonding?
Both covalent and ionic bonding use the octet rule, so that there is a full complement of valence electrons around each atom in the molecule. For example, a molecule of fluorine consists of 2 fluorine atoms with a covalent bond between them. Each atom has 7 electrons in its outer shell, but share one of the electrons between them.
How Is Covalent Bonding Different than Ionic Bonding?
In covalent bonding, electrons are shared between atoms rather than donated from one ion to another. This means that even if the molecules are dissolved in water, they will not break apart into ions. Compare the differences between salt water and sugar water. Salt water will conduct electricity, because the ionic bonds dissolve, but sugar water will not.
What Are Multiple Covalent Bonds?
The simplest covalent bonds are single covalent bonds, such as those in fluorine or in ammonia (NH3). In ammonia, each nitrogen atom is bonded to three hydrogen atoms, so that each hydrogen atom shares electrons with the nitrogen atom in a single bond. Some compounds, such as formaldehyde (H2CO), have a double bond between the carbon atom and the oxygen atom. They share two electrons between then, and then one electron between the carbon atom and the hydrogen atoms. Some compounds even have triple bonds. Quadruple bonds or higher do not occur naturally.
What Are Polar Bonds?
Polar bonds occur when electrons are bound more closely to one atom in a molecule than another. One of the most common covalent compounds is water, or H2O. Each hydrogen atom forms a covalent bond with the oxygen atom, but the oxygen atom draws the electrons closer to it than to the hydrogen atoms. They share electrons but not equally.
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