3.1 Matter And Substances I. Atom A. Def- the smallest unit of matter that cannot be broken down by chemical means. B. Atomic structure 1. Protons = 2. Neutrons = 3. Electrons = + charge neutral or no charge - charge

1. Made up of all the same atoms a. ex- 24 karat gold 4. Protons & Neutrons have same mass and are found in the nucleus. 5. Electrons are 1/1000 the mass of protons & neutrons. Found in electron clouds around the nucleus. C. Elements 1. Made up of all the same atoms a. ex- 24 karat gold 2. Isotopes have extra neutrons a. makes atom bigger, no change in overall charge.

II. Chemical Bonds A. Valance electrons 1. Electrons in the outermost energy level. 2. This level wants to fill to 8 electrons. B. Compounds 1. Made up of two or more element

C. Covalent Bonding 1. The sharing of electrons 2. A molecule is a group of atoms held together by a covalent bond 3. Not all substances that have covalent bonds are compounds. a. O2 covalent bond, not a compound b. CO2 covalent bond, compound

D. Ionic Bonding 1. gain or lose electrons 2. ion – positively or negatively group of atoms. 3. ionic bond is the attractive force between oppositely charged ions. 4. ex- table salt (NaCl) a. Sodium (Na+) - silver, soft metal that explodes in water b. Chlorine (Cl-) - green toxic gas

III. Polarity A. Molecules with partial charges on opposite ends are polar. B. Solubility 1. Water can dissolve polar molecules a. ex.- salt, sugar 2. Non-polar molecules do not dissolve in water. They instead clump together. a. ex.- oil, grease, wax

C. Hydrogen Bonds 1. Stronger than attractions between other molecules but not as strong as a covalent bond. a. ex.- 2 strands of DNA are held together by hydrogen bonds between bases.