1. CHAPTER 2  The Chemical Basis of Life 2.1-2.6  Elements, Atoms & their Interactions Objectives:1) Describe the structure of an atom 2) Identify the differences between atoms, elements, ions, and compounds I. Elements A. Intro 1. What is it? a. A substance that can’t be broken down into simpler chemical substances 2. Example  Gold a. No matter what you do it will always be gold 1. Burn it, crush it into powder, treat it with chemicals, etc. B. Natural elements in living things 1. Out of 90 naturally occurring elements, only 25 are essential to living organisms C. Each element is identified with a 1 or 2 letter symbol 1. Carbon-C, Oxygen-O, Calcium-Ca

2. II. Compounds A. Intro 1. What is a compound? a. A substance that is composed of 2 or more different elements that are chemically combined

3. b. Water  H2O 1. 2 hydrogen atoms combined with 1 oxygen atom 2. Why do atoms bond/combine? a. To become more stable 1. An atom becomes more stable when its outermost energy level is full a. Oxygen 1. Only has 6 electrons in outermost shell, it wants 2 more 2. It gets 2 more by sharing them with hydrogen  H2O

4. III. Atoms: The building blocks of elements A. Atom 1. The smallest particle of an element that has the characteristics of that element B. The structure of an atom/subatomic particles 1. Nucleus a. The center of the atom b. Composed of protons & neutrons 1. Protons  + charged particles 2. Neutrons  neutral, no charge 2. Electrons a. Found in the electron cloud b. - charged particle

5. C. Atomic number & Atomic mass 1. Atomic number a. The unique number of protons each element has 2. Atomic mass a. The number of all protons and neutrons that a particular element has D. Isotopes 1. Elements that have gained or lost a neutron 2. Have the same number of protons & electrons but differ in neutron # 3. Atomic number remains the same

6. III. Electron Arrangement A. The arrangement of electrons around the nucleus determines the chemical properties of a particular element 1. Electron cloud a. The space around the atom’s nucleus that is occupied by fast moving electrons b. Because electrons move so fast around the nucleus they appear as a cloud

7. B. Electron energy level 1. Regions or orbits around the nucleus in which electrons travel 2. Each energy level has a limited capacity for electrons 18 a. The first energy level 1. The smallest 2. Can hold a maximum of 2 electrons b. The second energy level 1. Can hold a maximum of 8 electrons c. The third energy level 1. Can hold a maximum of 18 electrons

8. 3. Electrons will always fill the first energy level first then move to the next a. Oxygen=8 electrons 1. 2 electrons in 1 st energy level 2. 6 electrons in 2 nd energy level 4. Atoms have no net charge a. They contain equal number of electrons & protons

9. I. How covalent bonds form A. What is a covalent bond? 1. The force that holds 2 atoms together when the share electrons 2. Most compounds in organisms have covalent bonds 3. Molecules a. A group of atoms held together by covalent bonds 2.7-2.10  Element Bonding Objectives:1) Distinguish between ionic, covalent, & hydrogen bonds. 2) Explain the properties of each type of bond

10. B. Bond Types 1. Electronegativity a. Atoms within an element are constantly pulling on their shared electrons b. The degree to which an atom pulls on an electron is referred to its electronegativity 1. The more a particular atom pulls on an electron the more electronegative it is 2. Nonpolar covalent bond a. Electrons are shared equally between the elements b. Electronegativity is equal between the atoms 3. Polar covalent bond a. Electrons are NOT shared equally between elements 1. Electrons spend more time around one of the elements than the other b. Creates a polar molecule 1. A molecule that has an unequal distribution of charge 2. For example, H 2 O

11. II. How ionic bonds form A. What is an ion? 1. An atom that has lost or gained an electron a. It now will have a charge 2. A charged particle B. Ionic bonding 1. The attractive force between 2 ions of opposite charge 2. Example  Sodium Chloride (NaCl) a. Na-11 electrons Cl-17 electrons (1 in outer level) (7 in outer level) b. Na needs to loose 1 electron Cl needs to gain 1 electron c. Na gives 1 electron to Cl making Na happy and Cl happy 1. However, Na now has a positive charge and Cl now has a negative charge 2. The difference in charge is what attracts them to each other creating an ionic bond

12. III. Hydrogen Bonds A. Formation 1. A + charged hydrogen in a polar covalent bond is attracted to the – charged atom of another molecule with polar covalent bonds a. In other words, a bond involving hydrogen that gets formed due to the electronegativity between hydrogen and another molecule 3. Example-H 2 O 2. Weak bonds

13. 2.11-2.14  Water’s Life-Supporting Properties Objectives:1) Describe why water is polar 2) Describe water’s unique features I. Water’s polarity A. Because water is polar 1. It attracts each other 2. It attracts ions 3. It attracts other polar molecules B. Why is being polar a big deal? 1. Due to its attraction for itself and other molecules, water can dissolve a variety of ionic (salt) and polar molecules (sugar) 2. Water’s attraction for itself a. + charged hydrogen on one water molecule attracts the – oxygen off another water molecule 1. This forms a hydrogen bond a. A very weak bond b. Cohesion c. Surface tension

14. 3. Waters attraction to other molecules a. Adhesion b. Solvent of life 1. Solvent a. A dissolving agent 2. Solute a. A substance being dissolved

15. II. Water resists temperature change A. Requires more heat to increase temp. compared to most other substances B. Losses a lot of heat as it cools C. Why important? 1. Considering cells are surrounded by water, water provides a constant env. for cells 2. Considering 71% of earth’s surface is covered with water, water moderates temperatures worldwide III. Ice less dense than water A. Water expands when it freezes 1. Ice is less dense that water causing it to float a. Causes cycling of the worlds water supply 2. As ice expands it has the ability to break rock a. Increases erosion  the cycling of soil

16. 2.15  Acids & Bases Objectives:1) To be able to distinguish between acids, bases, & buffers 2) To be able to explain and utilize the pH scale I. Acids A. Any compound that donates H + ions into a solution B. Acidic solutions, therefore, are solutions that….. 1. Solutions that have a high [ ] of H + (Acidic) II. Bases A. Any compound that accepts H + and removes them from a solution B. Basic solutions, therefore, are solutions that…… 1. Solutions that have a low [ ] of H + (Basic or Alkaline) III. Buffers A. Substances that minimize changes in pH 1. How? a. They accept H + when….. b. The donate H + when…...

17. IV. pH scale (potential for hydrogen) A. Reflects the relative [ ] of H + & OH - 1. H + & OH - [ ] are opposite one another B. Scale ranges from 0 – 14 1. 0 = Acidic 2. 14 = Basic 3. 7 = Neutral C. Scale factor 1. Each unit on the scale is a factor of 10 a. A tenfold increase in H + [ ]