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chemical formula, name is prefixed by number of atoms present. CO: carbon monoxide. SiO. 2. : silicon dioxide. NI. 3. : nitrogen triiodide.
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A chemical formula gives the numbers and types of atoms that are found in a substance. When the substance is a discrete molecule, then the chemical formula is also its molecular formula. Fe (iron) is a chemical formula Fe 2
3 is a molecular formula
The chemical formulas of most of the elements are simply their elemental symbol: Na (sodium) Fe (iron) He (helium) U (uranium) These chemical formulas are said to be monatomic—only an atom in chemical formula
A binary compound is one composed of only two different types of atoms. Rules for binary compound formulas
3 Fe 3
4
2
4
4
However, the preceding rule is often ignored when writing organic formulas (molecules containing carbon, hydrogen, and maybe other elements) in order to give a better idea of how the atoms are connected: C 2
6 O is the molecular formula for ethanol, but nobody ever writes it this way—instead the formula is written C 2
5 OH to indicate one H atom is connected to the O atom.
Very often, chemists use structural formulas to show where the atoms in a molecule are positioned. The atoms are connected to each other with bonds. Bonds represent the attractive forces that hold molecules together. There are three types of structural formulas: line structures, ball-and-stick models, and spacing-filling models.
For organic molecules, the carbon atoms are often not shown. C-H bonds are also omitted in line structures.
Atoms are represent by balls that are color-coded and are approximately the correct relative size of the atoms. This gives a better perspective of the space available in a molecule.
When hydrogen combines with elements from groups 1 or 17, a diatomic molecule results. The molecule is named according to the previous rules for nonmetallic binary compounds: NaH: sodium hydride HCl: hydrogen chloride LiH: lithium hydride
When hydrogen combines with elements from groups 2 or 16, the resulting molecule contains 2 H atoms. The molecule is named according to the previous rules for nonmetallic binary compounds, but the di is omitted: H 2 S: hydrogen sulfide CaH 2 : calcium hydride Exception is oxygen: H 2 O: water H 2 O 2 : hydrogen peroxide
