# 2.1: Chemical Symbols and Formulas

## Chemical Symbols and Formulas

To illustrate chemical reactions and the elements and compounds involved in them, chemists use symbols and formulas. A chemical symbol is a one- or two-letter designation of an element. Some examples of chemical symbols are $$\ce{O}$$ for oxygen, $$\ce{Zn}$$ for zinc, and $$\ce{Fe}$$ for iron. The first letter of a symbol is always capitalized. If the symbol contains two letters, the second letter is lower case. The majority of elements have symbols that are based on their English names. However, some of the elements that have been known since ancient times have maintained symbols that are based on their Latin names, as shown below.

Chemical Symbol Name Latin Name
Table 1: Symbols and Latin Names for Elements
$$\ce{Na}$$ Sodium Natrium
$$\ce{K}$$ Potassium Kalium
$$\ce{Fe}$$ Iron Ferrum
$$\ce{Cu}$$ Copper Cuprum
$$\ce{Ag}$$ Silver Argentum
$$\ce{Sn}$$ Tin Stannum
$$\ce{Sb}$$ Antimony Stibium
$$\ce{Au}$$ Gold Aurum
$$\ce{Pb}$$ Lead Plumbum

## CHEMICAL FORMULAS FOR COMPOUNDS

Compounds are combinations of two or more elements. A chemical formula is an expression that shows the elements in a compound and the relative proportions of those elements. Water is composed of hydrogen and oxygen in a two to one ratio. The chemical formula for water is $$\ce{H_2O}$$. Sulfuric acid is one of the most widely produced chemicals in the United States and is composed of the elements hydrogen, sulfur, and oxygen. The chemical formula for sulfuric acid is $$\ce{H_2SO_4}$$.

## Classification of compounds according to their molecular structure

Based on the number of atoms, molecules can be classified as:

• Monoatomic molecule: contains only one atom. Example: Ar
• Diatomic molecules: two atoms. Example: Cl2
• Triatomic molecules: three atoms. Example: CO2
• Polyatomic molecules: four or more types of atoms. Example: H2SO4

## Summary

A chemical symbol is a one- or two-letter designation of an element. Compounds are combinations of two or more elements. A chemical formula is an expression that shows the elements in a compound and the relative proportions of those elements. Some elements have symbols that derive from the Latin name for the element.

## Explore More

1. What is a chemical formula?

2. What is the chemical formula for glucose? What does this formula signify?

3. What is the chemical formula for caffeine?

4. What is the chemical formula for sugar?