Biology:

1. Biology: • You need to study your notes and vocab. • Make sure you know the following things: • What is a period? What does it represent? • What is a family? What does it represent? • What is atomic mass? • If you know the atomic number and atomic mass, what else do you know?

2. Pop Quiz: • Selenium’s (Se) atomic number is 34. Its atomic mass is 79. Its period is 4, its family is 6. • On your paper, answer the following questions: • How many protons does Se have? • How many electrons does Se have? • How many neutrons does Se have? • How many orbitals does Se have? • How many electrons are in its outer orbital?

3. C2.a Types of Chemical Bonds

4. Chemical Bonds: • Atoms in compounds are held together by bonds. • This is where electrons become important…

5. The Octet Rule: • The octet rule states that elements gain or lose electrons to attain an electron configuration of the nearest noble gas. Remember, the noble gases are Family 8, so they have 8 electrons in their outer orbital.

6. Valence electrons… • Valence electrons are electrons that are available to form bonds. • They are the electrons furthest to the outside of the atom (outer orbital). • The electrons that are the nearest to the nucleus are held more tightly than those farther away and cannot leave orbit.

7. Ions: • Remember when I said atoms like to have equal numbers of protons and electrons. • Well… that’s not always the case… • An ion is an atom or molecule with a net electric charge (either positive or negative) due to the loss or gain of one or more electrons.

8. Ions (con’t): • An atom that gains an electron has a negative charge. • An atom that loses an electron has a positive charge.

9. Ionic Bonds: • An ionic bond is a bond formed when electrons are transferred from one atom to another (gain/lose e-); the attraction between oppositely charged ions. • Usually when metals bond with nonmetals.

10. Example:

11. Covalent Bonds: • A covalent bond forms when electrons are shared between atoms. • Usually when nonmetals bond together.

12. Example:

13. Hydrogen Bonds: • Not actually a bond. • Chemical attraction in which the proton of a hydrogen atom of one molecule is attracted to an electronegative atom of another molecule. • Think H2O (water). • These bonds are weaker attractions than covalent or ionic bonds.

14. Hydrogen Bonds (con’t): • Hydrogen bonds have to involve hydrogen. • Will also involve an electronegative atom such as N (nitrogen), O (oxygen), or F (fluorine).

15. Example:

16. Chemical Reactions: C2.a

17. Chemical Reactions: • A chemical reaction involves either the making or breaking of chemical bond. • This is a process that changes one set of chemicals into another set of chemicals.

18. Chemical Reactions (con’t): • These occur slowly: • Iron + Oxygen -> Iron Oxide (rust) • Or they can occur quickly: • Hydrogen gas + Oxygen -> EXPLOSION

19. Chemical Reactions (con’t): • The elements or compounds that enter into a chemical reaction are called reactants. • The elements or compounds that are produced by a chemical reaction are called products. • H2O + CO2 -> O2+ C6H12O6 Reactants Products

20. Chemical Reactions (con’t): • Law of Conservation of Energy: energy can neither be created nor destroyed… • So energy is released or absorbed whenever a chemical bonds are broken or formed.

21. Balancing Equations: • Since atoms aren’t typically destroyed or created, you must have the same number of an element before and after a chemical reaction occurs. • This is called balancing chemical equations.

22. Balancing Equations: • Subscripts: little numbers; come after the element; represent the number of atoms of that elements; CANNOT be changed. • Coefficients: big numbers; come at the beginning of an element or compound; think multiplication; CAN be changed.

23. Balancing Equations (con’t): • Add coefficients in front of the compounds to balance the following equation: • H2O + CO2 -> O2+ C6H12O6