Compounds Compounds • Substance formed by the chemical combination of two or more elements in definite proportions • Example: WATER! • Water is NOT an element! Made up of 2 elements!! CaCO3 • Calcium carbonate – How many atoms of calcium? – How many atoms of carbon? – How many atoms of oxygen? LET’S CHECK YOUR BELLRINGER ALMOST ALL ELEMENTS EXIST IN A COMPOUND FORM. MOLECULE • Structure that results when atoms join together. • Smallest unit of most compounds. Why do compounds form? • Stability VALENCE ELECTRONS = ELECTRONS IN THE OUTERMOST RING PERIODIC TABLE IS ORGANIZED ACCORDING TO REACTIVITY…OR THE # OF VALENCE ELECTRONS IN ORDER TO BE STABLE, THE OUTERMOST ELECTRON RING MUST BE COMPLETELY FILLED. ATOMS IN COMPOUNDS ARE HELD TOGETHER BY BONDS. LET’S MAKE ONE OF THE MOST PREVALENT COMPOUNDS IN YOUR BODY! Bond Types • There are two types of bonds: – Ionic – Covalent Remember… • Why do atoms bond in the first place? • What is the key subatomic particle involved in bonding? What is going on in each picture? Which picture would best match IONIC BONDS? Which picture would best match COVALENT BONDS? A B Ionic Bonds • Formed when one or more electrons are transferred from one atom to another. (ions) • The resulting oppositely charged ions are attracted to each other – forming the bond Covalent Bonds • Forms when electrons are shared between atoms. Covalent Bonds • Most commonly found bond in compounds that make up living things.