1. Unit 1 The Chemistry of Life Chapters 2-5

2. Chapter 2 The chemical context of life You must know: The 3 subatomic particles & their significance The types of bonds, how they form, & their relative strengths

3. 2.1 Matter consists of elements in pure forms Matter consists in combinations called compounds

4. What is matter? Anything that has mass and takes up space Living or nonliving Element Substance that cannot be broken down to other substances by chemical reactions Periodic Table

6. Compound A substance consisting of two or elements combined in a fixed ratio: Example: Water H 2 O or Table Salt NaCl A compound has characteristics different from those of its elements Molecule A molecule is formed when two or more atoms join together chemically Example: Molecular hydrogen (H 2 ), molecular oxygen (O 2 ) and molecular nitrogen (N 2 ) *** All compounds are molecules but not all molecules are compounds

8. C, H, O, N Make up 96% of living matter 25 of the 92 Natural elements are essential to life The rest are trace elements Example: Fe & I

11. 2.2 Properties of an element depend on the structure of its atoms Atoms Smallest unit of an element that retains the property of the element Made up of Protons, Neutrons, & Electrons

12. Protons Positively charged Found in the nucleus Determine the element

13. Electrons Negatively charged Found in electron shells (or electron cloud) Determine chemical properties Determine reactivity of the element

14. Neutrons Have no charge Found in the nucleus The number can vary in the same element – called ISOTOPES Example: 12 C and 14 C are isotopes of Carbon – both have 6 protons, but 12 C has 6 neutrons & 14 C has 8 neutrons

17. Atomic number The number of protons an element has Unique to every element Also the number of electrons – why? Mass number The sum of its protons & neutrons How we determine isotopes

18. 2.3 Formation and function of molecules depend on chemical bonding Chemical bond Interactions between the valence electrons (outermost electrons) of different atoms Atoms are held together by chemical bonds to form molecules Two main types of bonds: Ionic Covalent

19. Ionic bonds 2 atoms attract valence electrons so unequally that the more electronegative atom steals the electron away from the less electronegative atom An ion is the resulting charged atom or molecule Cation = positive Anion = negative Ionic bonds occur because these ions will be either + or – charged and they are attracted – why? Example – see board

22. Covalent bond When valence electrons are SHARED Can share 1, 2, or 3 electrons Nonpolar CB When the shared electrons are shared equally Example: O = O or H-H Polar CB When there is unequal sharing of electrons Example: Water – causes the O to be slightly - & the H’s are slightly +

24. Other bonds: Hydrogen Weak bonds that form between the positively charged H atom of one molecule & the strongly (–) O or N of another Van der Waals interactions Very weak, transient connections that are results of asymmetrical distribution of electrons within a molecule Contribute to the 3-D shape of large molecules (ch 5)

25. 2.4 Chemical reactions are the making and breaking of chemical bonds The starting molecules of a chemical reaction are called reactants The final molecules of a chemical reaction are called products

27. Some chemical reactions go to completion: all reactants are converted to products All chemical reactions are reversible: products of the forward reaction become reactants for the reverse reaction Chemical equilibrium is reached when the forward and reverse reaction rates are equal *** Photosynthesis & Cellular Respiration ***