Representing Elements and Simple Molecules

Atomic, Molecular, and Ionic Symbols

Atoms are represented by their element symbol, e.g. H for hydrogen, O for oxygen.
Molecules that consist of two atoms are denoted by the element symbol and a subscript number, e.g. H2 for hydrogen molecule, O2 for oxygen molecule.
Ions are denoted similar to atoms but with a superscript indicating the charge, e.g. Na+ for sodium ion, O2- for oxide ion.

Compounds and Molecules

Compounds are represented by the symbols of the elements involved with a subscript indicating the number of atoms involved, e.g. H2O for water with two hydrogen atoms and one oxygen atom.
A group of atoms bonded together is called a molecule, and they are also represented similarly, e.g. CH4 for methane.

Structural and Molecular Formulas

Structural formulas show the arrangements of atoms within a molecule e.g. water can be represented as H-O-H.
For bigger molecules, condensed structural formulas can be used to show the arrangement, e.g. ethane can be represented as CH3-CH3.
Molecular formulas show only the number of each type of atom in a molecule, e.g. ethane is C2H6.

Use of Brackets

Brackets with a subscript outside show that the atoms within the brackets are repeated that number of times, e.g. Ca(OH)2 represents calcium hydroxide with two hydroxide ions OH.

Remember, it’s crucial to understand and use these representations correctly as they are the foundation for more complex concepts in chemistry. Become proficient in representing and interpreting these symbols and formulas.