CHAPTER 2 The Chemical Basis of Life

2.1-2.6 Elements, Atoms & their InteractionsObjectives: 1) Describe the structure of an atom

2) Identify the differences between atoms, elements, ions,and compounds

I. ElementsA. Intro

1. What is it?a. A substance that can’t be broken down into simpler chemical

substances2. Example Gold

a. No matter what you do it will always be gold1. Burn it, crush it into powder, treat it with chemicals, etc.

B. Natural elements in living things1. Out of 90 naturally occurring elements, only 25 are essential to living

organisms

C. Each element is identified with a 1 or 2 letter symbol1. Carbon-C, Oxygen-O, Calcium-Ca

II. CompoundsA. Intro

1. What is a compound?a. A substance that is composed of 2 or more different elements that

are chemically combined

b. Water H2O1. 2 hydrogen atoms combined with 1 oxygen atom

2. Why do atoms bond/combine?

a. To become more stable1. An atom becomes more stable when its outermost energy level

is fulla. Oxygen

1. Only has 6 electrons in outermost shell, it wants 2 more2. It gets 2 more by sharing them with hydrogenH2O

III. Atoms: The building blocks of elementsA. Atom

1. The smallest particle of an element that has the characteristics of that element

B. The structure of an atom/subatomic particles1. Nucleus

a. The center of the atomb. Composed of protons & neutrons

1. Protons + charged particles2. Neutrons neutral, no charge

2. Electronsa. Found in the electron cloudb. - charged particle

C. Atomic number & Atomic mass1. Atomic number

a. The unique number of protons each element has2. Atomic mass

a. The number of all protons and neutrons that a particular element has

D. Isotopes1. Elements that have gained or lost a neutron2. Have the same number of protons & electrons but differ in neutron #3. Atomic number remains the same

III. Electron Arrangement A. The arrangement of electrons around the nucleus determines the

chemical properties of a particular element1. 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

B. Electron energy level1. Regions or orbits around the nucleus in which electrons travel2. Each energy level has a limited capacity for electrons

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a. The first energy level1. The smallest2. Can hold a maximum of 2 electrons

b. The second energy level1. Can hold a maximum of 8 electrons

c. The third energy level1. Can hold a maximum of 18 electrons

3. Electrons will always fill the first energy level first then move to the nexta. Oxygen=8 electrons

1. 2 electrons in 1st energy level2. 6 electrons in 2nd energy level

4. Atoms have no net chargea. They contain equal number of electrons & protons

I. How covalent bonds formA. What is a covalent bond?

1. The force that holds 2 atoms together when the share electrons

2. Most compounds in organisms have covalent bonds3. 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

B. Bond Types1. 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 electronegativity1. The more a particular atom pulls on an electron the more

electronegative it is2. Nonpolar covalent bond

a. Electrons are shared equally between the elementsb. Electronegativity is equal between the atoms

3. Polar covalent bonda. Electrons are NOT shared equally between elements

1. Electrons spend more time around one of the elements than the other

b. Creates a polar molecule1. A molecule that has an unequal distribution of charge2. For example, H2O

II. How ionic bonds formA. What is an ion?

1. An atom that has lost or gained an electrona. It now will have a charge

2. A charged particle

B. Ionic bonding1. The attractive force between 2 ions of opposite charge

2. Example Sodium Chloride (NaCl)

a. Na-11 electronsCl-17 electrons

(1 in outer level) (7 in outer level)

b. Na needs to loose 1 electronCl needs to gain 1 electron

c. Na gives 1 electron to Cl making Na happy and Cl happy1. However, Na now has a positive charge and Cl now has a negative

charge2. The difference in charge is what attracts them to each other

creating an ionic bond

III. Hydrogen BondsA. Formation

1. A + charged hydrogen in a polar covalent bond is attracted to the – charged atom of another molecule with polar covalent bondsa. In other words, a bond involving hydrogen that gets formed due to

the electronegativity between hydrogen and another molecule

3. Example-H2O

2. Weak bonds

2.11-2.14Water’s Life-Supporting PropertiesObjectives: 1) Describe why water is polar

2) Describe water’s unique features

I. Water’s polarityA. Because water is polar

1. It attracts each other2. It attracts ions3. 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 itselfa. + charged hydrogen on one water molecule attracts the – oxygen

off another water molecule1. This forms a hydrogen bond

a. A very weak bondb. Cohesion

c. Surface tension

3. Waters attraction to other moleculesa. Adhesion

b. Solvent of life1. Solvent

a. A dissolving agent2. Solute

a. A substance being dissolved

II. Water resists temperature changeA. Requires more heat to increase temp. compared to most other

substancesB. Losses a lot of heat as it cools

C. Why important?1. Considering cells are surrounded by water, water provides a

constant env. for cells2. Considering 71% of earth’s surface is covered with water, water

moderates temperatures worldwide

III. Ice less dense than waterA. Water expands when it freezes

1. Ice is less dense that water causing it to floata. Causes cycling of the worlds water supply

2. As ice expands it has the ability to break rocka. Increases erosion the cycling of soil

2.15 Acids & BasesObjectives: 1) To be able to distinguish between acids, bases, & buffers

2) To be able to explain and utilize the pH scale

I. AcidsA. Any compound that donates H+ ions into a solutionB. 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 solutionB. Basic solutions, therefore, are solutions that……

1. Solutions that have a low [ ] of H+ (Basic or Alkaline)

III. BuffersA. Substances that minimize changes in pH

1. How?a. They accept H+ when…..b. The donate H+ when…...

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 = Acidic2. 14 = Basic3. 7 = Neutral

C. Scale factor1. Each unit on the scale is a

factor of 10a. A tenfold increase in H+

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