1. Unit: The Chemistry of Living Things

2. I. Composition of Matter Matter—anything that occupies space and has mass Elements—fundamental units of matter ◦ About 96% of an organism is made from four elements  Carbon (C)  Oxygen (O)  Hydrogen (H)  Nitrogen (N)

3. Composition of Matter Atom: smallest unit in which an element may be divided while retaining all of the characteristic properties of that element.

4. Atomic Structure Nucleus ◦ Protons (p +, +1) ◦ Neutrons (n 0 ) Outside of nucleus Electrons (e -, -1) Atomic number= # number of protons * Each element has a unique atomic number.

5. 2. Neutrons and Protons have significant mass. A proton has a mass of 1 AMU A neutron has a mass of 1 AMU An electron has negligible mass Mass #= protons + neutrons

6. 3. Location Neutrons & protons -nucleus. Electrons orbit nucleus in patterns within electron shells. # of shells an atom has is determined by # of electrons Electron shells AKA energy levels since shells closet to the nucleus have the least energy; those farthest away have the most.

7. 4. Energy Levels Each energy level (shell) holds: ◦ Level 1 can hold a maximum of 2 electrons ◦ Level 2 can hold a maximum of 8 electrons ◦ Level 3 can hold a maximum of 18 electrons

8. Octet Rule ◦ Electrons will follow the Octet rule or rule of eights:  Energy levels > shell 2 can contain more than eight electrons  BUT # of electrons that can participate in bonding (outer shell) is still limited to a total of 8.

9. Electrical charge of an atom Ions – atoms with an electrical charge ◦ Charged particles  Anions are negative  Cations are positive  Either donate or accept electrons  Ions in the body are known as electrolytes

10. Elements Element: a substance that cannot be ordinarily broken down chemically to form simpler kinds of matter.

11. 1. Atomic Number (# of protons) Nucleus contains a fixed # of protons. # of protons in nucleus is the primary determining factor for the general characteristics of an atom. Atoms with the = # of protons in the nucleus are the same element, regardless of whether they have the same #s of neutrons or electrons. The atomic # is written as a subscript to the left of its atomic symbol, i.e. Helium has 2p+, ( 2 He).

13. 2. Chemical Symbol Rules: a. 1 or 2 letters are used to represent an element. b. If 1 letter is used to represent an element it is capitalized. c. If 2 letters are used to represent an element, the first letter is uppercase and the second letter is always lowercase

14. Isotopes and Atomic Weight  Elements w/2+ variants are Isotopes  Isotopes of an element have the same atomic number but vary in their mass numbers; thus, all isotopes of an element have the same number of protons, but differ in the number of neutrons  I.e.: The most abundant isotope of hydrogen is 1 H. However, some hydrogen atoms have a mass of 2 or 3, which means they have 1 proton and 1 or 2 neutrons respectively.

15. Isotopes and Atomic Weight Uses of Isotopes -Carbon dating – fossils, organic remains -Medical imaging

16. Atomic weight  Atomic mass is the average of the relative masses of all the isotopes of an element  The atomic mass is written as a superscript to the left of its atomic symbol. The atomic mass of an element is =P + N The atomic weight of hydrogen is 1.008. Thus, the lightest isotope 1 H is present in much greater amounts in our world than its 2 H or 3 H forms.

17. Definitions Molecule: the simplest structural unit of a single element (O 2 ) or compound (CO 2 ) ◦ Compound: a pure substance made up of atoms of 2 or more elements. (Literally means “to put together”)

18. 1. Atoms in a Compound In a compound, the proportions of each kind of atom are fixed. ◦ Chemical formula: gives the kind and proportion of atoms of each element in the compound ◦ EXAMPLE: H 2 O (there are 2 hydrogen atoms for every 1 oxygen atom in the compound water).

19. Structural formula: an expanded molecular formula showing the arrangement of atoms within the molecule

20. 2. Properties of Compounds The physical and chemical properties of compounds differ from those of the individual elements that compose it ◦ Example: Oxygen and hydrogen are usually found as gases, however when they combine, they form a liquid.

21. D. Chemical Bond: a chemical attachment between atoms Breaking and Forming Chemical Bonds ◦ During chemical reactions, bonds are broken, atoms are rearranged, and new chemical bonds are formed

22. Role of Electrons ◦ Elements combine and form bonds based on the number of electrons in their outermost shell. ◦ Valence is the number of single bonds an atom will usually form (generally = to the number of electrons required to fill outer shell). ◦ Most atoms are not naturally stable, so they undergo chemical bonding with other atoms to become more stable.

23. Chemical Equation Reactants are generally shown on the left side of the equation Products are shown on the right The arrow means “yields”

24. 2. Bonding for Stability ◦ Atom is stable when its outer energy level (valence shell) is “filled”. ◦ Incomplete valence shell are unstable and therefore chemically reactive. ◦ To fill their valence shells, they form bonds by sharing or transferring e - with other atoms.

25. Examples of elements that do not form bonds.

26. 3. Covalent Bond: a bond that forms when two atoms share one or more pairs of electrons. Nonmetals form covalent bonds.

27. Covalent Bonds A line drawn between chemical symbols represents a covalent bond (-). Single, double, and triple covalent bonds A molecule = 2+ atoms held together by covalent bonds.

28. Oxygen needs 2 electrons to be stable. So, it will share 4 VEs or 2 pair= double bond

29. Exercise: Finish the electron shell diagrams for N 2, H 2 O, and CO 2.

31. Note the two pairs (4 electrons) shared between each of the atoms.

33. 4. Ionic Bond: a bond formed by electrical attraction between two oppositely charged ions. Remember, an ion is an atom or molecule with an electrical charge. Opposites attract Electron(s) are transferred from one atom to another

35. Use the practice sheet to form ionic bonds. Animation: Bonding in an Erlenmeyer Flask. Animation: Bonding in an Erlenmeyer Flask.