Elements, Compounds and chemical formulas

Review: What is a Element? Element - a pure substance that is made up ONE type of atom. Note: If there is more than one atom of the SAME element, it is called a “molecule” – It is NOT a compound.

Review: What is a compound? Compound - a pure substance that is made up of 2 or more DIFFERENT types of atoms (elements). When compounds form, a chemical reaction has occurred.

What are chemical Formulas? The formula of a compound identifies the elements in the compound and the ratios in which their atoms are present. How many atoms of each element are present in each of these compounds 

WHY do Elements form Compounds? … To become more stable! Example: Na is flammable and Cl2 is a toxic gas. They combine to form NaCl (Sodium Chloride) NaCl is a very stable compound that is neither flammable nor toxic

What if a Compound is unstable? If compounds are unstable, then they will break down to form stable elements. Example: H2O2 (Hydrogen Peroxide) will break down into Water (H2O) and release the extra Oxygen atom as a gas.

Magnesium Hydroxide – Mg(OH)2 Mg = 1 O = 2 H = 2 Aluminum Oxide – Al2O3 Al = 2 O = 3 Calcium Bromide – CaBr2 Ca = 1 Br = 2 Sulfuric Acid – H2SO4 H = 2 S = 1 O = 4 Magnesium Hydroxide – Mg(OH)2 Mg = 1 O = 2 H = 2 Ammonium Phosphate – (NH4)3PO4 N = 3 H = 12 P = 1 O = 4 Iron Sulfate – Fe2(SO4)3 Fe = 2 S = 3 O = 12 Chemical Formulas *When a subscript is outside of a parenthesis, then it multiplies to both of the elements.