2. Atomic Structure Review Atoms are the simplest form of matter. The center is called the nucleus The area outside the nucleus is the cloud

3. Atomic Structure LocationParticleChargeMass nucleusProton+11 nucleusNeutron01 cloudElectron0 Why are atoms neutral? # of protons = # of electrons

4. the atomic number is the number of protons the mass number is the sum of the protons and neutrons Isotopes are atoms of the same element, but with different masses

5. Elements are pure substances that cannot be broken down any further each element has a one- or two-letter symbol 96% of living organisms are made of 4 elements: carbon, hydrogen, oxygen, nitrogen the remaining 4% contain some essential and trace elements (ex. iodine, calcium, zinc)

6. Compounds are substances composed of 2 or more atoms that are chemically combined Chemical bonds hold atoms together in a compound atoms that share electrons form covalent bonds

7. atoms that transfer electrons form ionic bonds  ions are atoms that have lost or gained electrons, giving them a charge (ex: K +, Na +, H +, Cl - )

8. Chemical Reactions A chemical equation is used to represent a reaction 2H 2 O 2  2H 2 O + O 2 (reactants)  (products) the coefficient = the # of molecules

9. Properties of Water 1. Water is a polar molecule

10. 2. Water forms hydrogen bonds

11. Cohesion occurs when water is attracted to water(beads) Adhesion occurs when water is attracted to some other substance - Both are used by plants to transport water

12. 3. Water is less dense as a solid (ice floats)

13. 4. Water can dissolve most substances, making it the universal solvent These are known as aqueous solutions

15. The water molecule separates into two different ions: H 2 O  H + + OH - (H + )hydrogen ions and (OH - ) hydroxide ions

16. the pH scale measures the amount of H + Acids (pH 0 – 6.9) Taste sour Feel like water Bases (pH 7.1 – 14) Taste bitter Feel slippery Strong base Strong acid