A structural formula visually represents how atoms in a compound are bonded. Types include electron dot, linear bond, condensed, and skeletal formulas. Bonds can be covalent, double, or lone pairs. Different formulas represent these components through dots, lines, or symbols.
The structural formula of a chemical compound is a visual representation showing how the atoms of that compound are bonded together. It is often more useful than the molecular formula, which indicates the atoms and their quantities but not their arrangement in space. For example, the molecular formula of water, H2O, shows that there are two hydrogen atoms (H) and one oxygen atom (O) in the molecule, but it doesn’t show how they are arranged or bonded. There are several types of structural formulas, including electron dot diagram, linear bond structural formula, condensed structural formula, and skeletal structural formula.
Atoms often bond with each other by sharing a pair of electrons, forming a covalent bond. They can also form a double bond, in which four electrons are shared instead of two. In some cases, not all electrons are shared in bonds between atoms in a compound. Such loose pairs of electrons are called lone pairs. The structural formula of a chemical compound visually represents each of these different components through a system of dots or lines.
In an electron dot diagram, all of the external or valence electrons available for bonding are represented by dots around the chemical symbol of the atom. An oxygen atom has six electrons in its valence shell, so it would be represented by an O surrounded by six dots: two at the top and bottom, and one on each side. When oxygen bonds to two hydrogen molecules to form water, the electrons of the hydrogen are shared in covalent bonds. Since each hydrogen has one valence electron, the new electron dot plot appears as a central O surrounded by eight dots, two on each of the four sides, and an H to the left and right, signifying that these atoms are covalently bonded .
A linear bonding structural formula replaces covalent bonds with straight lines and double bonds with a set of parallel lines. The linear bond formula for water would look like H—O—H, with the lone pairs of electrons represented by dots, two above and two below the O. This type of formula is also called a Lewis structure. Sometimes lone pairs are omitted from the line bond diagram for convenience.
Condensed structural formulas are useful for complicated molecules that would take up too much space if all bonds were shown. In this type of formula, some atoms are grouped together and only the essential bonds are drawn. Because atoms bond together in predictable ways based on their valence electrons, some bonds may be omitted when describing the structure of the molecule.
The skeletal formula goes one step further and omits all carbon and hydrogen atoms, showing only the chemical symbols of other groups connected by a line in a zigzag line structure. This type of formula is often convenient in organic chemistry, where molecules containing repeating chains of carbon and hydrogen atoms are common. In a skeletal formula, each carbon is represented by an angle in the line. If two lines extend from that angle, it is assumed that two hydrogen atoms are bonded to carbon. The empty end of the line indicates a carbon bonded to three hydrogen atoms.
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