W ARM U P The atomic mass of an element and the mass number of an atom often have similar values. However, atomic mass and mass number are not the same thing. Explain the difference.

W ARM U P Acids and bases are two kinds of chemical compounds. Compare and contrast at least four chemical and physical properties of acids and bases.

W ARM U P Why don’t the noble gases in Group 18 on the periodic table form chemical bonds?

W ARM U P You measured the mass of a steel pipe before leaving it outdoors. One month later, the pipe had rusted, and its mass had increased. Does this change violate the law of conservation of mass? Explain your answer.

C HEMICAL B ONDING Chapter 12

C HEMICAL B ONDING Sodium Atom

O CTET R ULE The number of valence electrons determines whether an atom will form bonds. The outermost energy level of an atom is considered to be full if it contains 8 electrons. Hydrogen and Helium only need 2 valence electrons for a full energy level. How many valence electrons are in the fluorine atom?

I ONIC B ONDS Ionic bonds form when electrons are transferred from one atom to another Ionic bonds form between metals and nonmetals

C OVALENT B ONDS Covalent bonds are formed when two atoms share one or more pairs of electrons Covalent bonds form between 2 nonmetals

M ETALLIC B ONDS Metallic bonds are formed by the attraction between positive metal ions and the electrons in the metal Electrons are not shared by adjacent atoms (atoms that are next to each other), but are free to “roam” This gives metals their ability to conduct electricity

C HEMICAL R EACTIONS Chapter 13 SPI Identify the reactants and products of a chemical reaction SPI Recognize that in a chemical reaction the mass of the reactants is equal to the mass of the products (Law of Conservation of Mass)

N EW S UBSTANCES

C HEMICAL F ORMULAS A chemical formula is a shorthand way to use chemical symbols and numbers to represent a substance Carbon dioxide = CO 2 Glucose = C 6 H 12 O 6 The subscript number tells you how many atoms of an element are in the compound

C HEMICAL F ORMULAS Reading check: What is the difference between CO and Co?

Subscripts – the number of atoms No number is understood to be “1” Coefficients – the number of molecules 3H 2 SO 4 = H 2 SO 4 6 – H, 3 – S, H 2 SO 4 = 2 – hydrogen 1 – Sulfur 4 – Oxygen coefficient subscript

C HEMICAL E QUATIONS The formulas of the reactants are written before the arrow The formulas of the products are written after the arrow The arrow, also called the yields sign, separates the reactants from the products

L AW OF C ONSERVATION OF M ASS

Which chemical equation best shows the law of conservation of mass? A. 3Al + 2CuO  Al 2 O 3 + 2Cu B. 2Al + 3CuO  Al 2 O 3 + 3Cu