1. Ch. 19.1 & 19.2 I. Bonding and Molecules A. Molecule-DEF- made up of more than one atom. B. Why do atoms form chemical bonds? 1. Atoms bond in order to become stable. a. Stable atoms have 8 valence electrons. i. One exception: the first energy level only holds 2 electrons. b. Octet rule- atoms form bonds in order to complete their octet and become stable.

2. C. Bohr’s Model 1. Bohr’s Model is named after the discoveries of a Danish Physicist Neils Bohr (1885-1962). a. He described electrons as moving around the nucleus in fixed orbits that have a set amount of energy. b. When looking at Bohr’s Model, the father the electrons are from the nucleus the more energy they have. c. Electrons orbit around the nucleus on circular rings that are referred to as orbitals or energy levels. d. The first energy levels can hold 2 electrons, the 2 nd can hold 8, the 3 rd -8, the 4 th -18, the 5 th -18, the 6th- 36 and so on. e. Electrons can “jump” to higher energy levels and then “fall” back to their original energy level.

3. C. Shortcut to find valence electrons… 1. Look at the group number. ( Peery #’s) a. Ex. Nitrogen-group 5…it has 5 valence electrons. b. Draw the Lewis Dot Diagram in order to see how many electrons an element needs in order to be stable. What is a Lewis Dot Diagram? c. It is a drawing that includes an elements’ symbol surrounded by dots that represent the number of valence electrons an element has. Ex. Nitrogen- on board. d. Nitrogen needs 3 more valence electrons in order to be stable. e. What element has three valence electrons? Ex. Aluminum- in group 3 Therefore, Nitrogen could bond with Aluminum to complete its outermost energy level and become stable. (This also, fulfills the Octet Rule)

4. A. Bonding with transition elements. 1. The group of elements in the middle of the periodic table are called transition elements. 2. There is no shortcut way to figure out the charge…so the charge has to be given to you in the problem. Ex. Copper (II). a. This example tells you that Copper would have a charge of positive 2. b. Transition elements will always HAVE a positive charge.

5. c. Roman numerals will always be used to tell you the charge. d. Transition elements can have more than one charge and be stable. Ex. Copper (II), Copper (I), Copper (IV). Why is why the charge has to be given to you. Lets try an example: Ex. 1 Write the chemical formula for Iron (III) Oxide.