Why Study Chemistry?

1. Elements, Atoms, and the Interaction of Matter Why Study Chemistry? • Life dependson chemical reactions. • Metabolism ~ process of breaking down and building up molecules that are essential to life. • The “WHY” and “HOW” of Biology can be viewed in terms of chemistry. • Chemistry can be used to describe structures and processes.

2. Elements • Everything is made up of elements. • An element is a substance that cannot be broken down into simpler substances. • Example: Gold (Au), Iron (Fe), Aluminum (Al) • 92 elements occur in nature, 25 of which are essential to living organisms.

3. Elements • Four elements are especially abundant. • Composition of human body: • Oxygen -- 65.0% • Carbon -- 18.5% • Hydrogen -- 9.5% • Nitrogen -- 3.5%

4. Atoms • Smallest unit of an element with the properties of that element. • Atoms are the building blocks of elements. • Atoms are made up of: • Protons (p+) -- Positive Charge • Neutrons (n0) -- No Charge (Neutral) • Electrons (e-) -- Negative Charge

5. Atoms • All atoms have the same general arrangement. Electrons (e- ) Protons (p+ ) Nucleus Energy Levels Neutrons (n0 )

6. Atoms • # of Protons = # of Electrons ~ Zero Charge • # of Protons is constant for an element. • e.g. Hydrogen = 1 Oxygen = 8 Carbon = 12 • # Protons = Atomic Number • # of Neutrons is NOT constant for all elements. • Different numbers = ISOTOPES. • Radioisotopes ~ isotopes with UNSTABLE nuclei • Some, not all, are radioactive, e.g., Carbon -14.

7. Interactions of Matter • Compound-- two or more elements chemically combined in a fixed ratio. • Compounds have properties that are different from the elements that formed them. • Two or more atoms bonded together in a compound = molecule, e.g. water (H2O). How elements combine to form compounds depends on the number and arrangement of electrons in atoms -- atoms are MOST STABLE when the outermost energy level contains EIGHT electrons (except hydrogen, which is stable when the outermost level contains TWO electrons).

8. Electron Structure of Atoms • Maximum number of electrons: • Energy level one: 2 electrons (s) • Energy level two: 8 electrons (s, p) • Energy level three: 18 electrons (s, p, d) • Energy level four: 32 electrons (s, p, d, f) • Four orbitals possible for energy levels: • s: 2 electrons • p: 6 electrons • d: 10 electrons • f: 14 electrons

9. Bonding Patterns • Covalent Bonds • two atoms share one or more pairs of electrons • Ionic Bonds • one atom loses an electron, one atom gains an electron ~ results in negative and positive ions which are attracted to one another • Hydrogen Bonds • a chemical bond in which a hydrogen atom of one molecule is attracted to an electronegative atom, especially nitrogen, oxygen, or fluorine

10. Covalent Bonds H20 molecule • Atoms share electrons, e.g. e- e- Oxygen e- Atomic # O = 6 Atomic # H = 1 e- e- e- e- e- e- e- Hydrogen Hydrogen

11. Covalent Bonds • Equal Sharing -- Nonpolar Molecule • Unequal Sharing -- Polar Molecule e- e- Oxygen e- Atomic # O = 6 Atomic # H = 1 e- e- Negative Charge e- e- e- e- e- Positive Charge Hydrogen Hydrogen Water is the one essential life-giving substance!

12. Ionic Bond • One atom loses an electron and one atom gains an electron -- crystal is formed. • One atom is left with a positive charge. • One atom is left with a negative charge. • Opposite charges hold atoms together. e- Na + Cl Na+ + Cl-

13. Hydrogen Bonds • Positive ends of polar molecules are attracted to negative ends of other polar molecules. • Bonds form, break, reform frequently. • Bonds are weak (1/20 covalent bond). • These bonds give water its unique properties. H Bonds - + + + + Covalent Bonds + - - + +

14. Mixtures • Substances do not combine chemically. • Solution -- one or more substances are distributed evenly in another substance, e.g. Kool-Aid (solute) in water (solvent). • Suspension -- heterogeneous mixture of finely divided particles of a solid temporarily suspended in a liquid, e.g., Sand in water. • Colloid -- solid particles are larger than in a solution, but smaller than in a suspension; particles do NOT settle out, e.g., Gelatin in water

15. Acids and Bases • pH -- a measure of how acidic or basic (alkaline) a substance is (scale 0-14). • Acid -- any substance that forms hydrogen ions (H+) in water • Example: HCl H+ + Cl- • pH < 7 • Base -- any substance that forms hydroxyl ions (OH-) in water • Example: NaOH Na+ + OH- • pH > 7

16. pH of Common Solutions pH Acidic 0 1 2 3 4 5 6 Neutral 7 8 9 10 11 12 13 Basic 14

17. Review “QUIZ” • The center of an atom is called the nucleus • Atoms of the same element with different numbers of neutrons are called isotopes • Any substance that forms hydrogen ions (H+) in water is called a(n) acid • Atoms of two or more elements chemically combined are compounds • Two atoms that share electrons are held together by bonds. covalent

18. Review “QUIZ” • A molecule with an unequal distribution of charge is a polar molecule • A mixture in which one substance is distributed evenly in another is a solution • Any substance that forms hydroxyl ions (OH-) in water is called a(n) base • When one atom loses an electron and another atom gains the electron, the atoms are held together by ionic bonds • The one essential life-giving substance is water