How to Count Atoms Symbol 1 The symbol

How to Count Atoms

Symbol 1. The symbol of an element represents one atom of that element. e. g. Na = 1 atom of Sodium

Subscript 2. A subscript is written behind the symbol of an element in the lower right corner. A subscript is used to indicate the number of atoms if there is more than one atom of the element. e. g. H 2 = 2 hydrogen atoms

Subscript outside a bracket 3. A subscript outside a bracket multiples all the elements inside the brackets. e. g. Mg 3(PO 4)2 Mg = _____ P= ___ 8 O= ___

Coefficient 4. A. A coefficient is a number written in front of a chemical symbol and indicates that number of atoms of that element. e. g. 3 C= b. A coefficient is a number written in front of a chemical formula and indicates the number of molecules of that compound

Chemical Formula • Chemical Formula- combination of symbols that represents the atoms in a compound • Note: A coefficient multiplies the number of atoms of each element in the formula

Examples • 2 H 20 _____ molecules of H 20 – _____H (hydrogen) – _____ O (oxygen)

Examples • Ca 3(PO 4)2 – _______ molecules of Ca 3(PO 4)2 – _______ Ca (Calcium) – _______ P (Phosphorus) – _______ O (oxygen)

Examples • Pb (NO 3)2 – _______ molecules of Pb(NO 3)2 – _______ Pb (Lead) – _______ N (Nitrogen) – _______ O (Oxygen)