2. Atom – the smallest unit of matter “indivisible” Helium atom WHAT ARE THESE REGIONS CALLED AGAIN?

3. electron shells a)Atomic number = number of Electrons a)What else does it tell us????? b)Electrons vary in the amount of energy they possess, and they occur at certain energy levels or electron shells. c)Electron shells determine how an atom behaves when it encounters other atoms

4. Remember 2818

5. the electrons of an atom that can participate in the formation of chemical bonds with other atomselectronsatomchemical bonds THESE ARE THE OUTERMOST ELECTRONS IN THE ATOM!!!

6. Determining # of Valence Electrons The number of valence electrons of an element is determined by its periodic table group (vertical column). The number within the unit's place identifies how many valence electrons are present in each group.periodic table group REMEMBER: We skip over the transition metals because they do not follow the rules.

7. Let’s Practice Elements in Group 1 should have how many valence electrons? Elements in Group 18 should have how many valence electrons? What about Group 16??? Pretty Simple, huh?

8. Electrons are placed in shells according to rules: 1)The 1st shell can hold up to two electrons, and each shell thereafter can hold up to 8 electrons. For Example: Let’s say shell 3 has 8 valence electrons…it would be considered FULL even though it can hold a maximum of 18

9. Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons C would like to N would like to O would like to Gain 4 electrons Gain 3 electrons Gain 2 electrons

10. Why are electrons important? 1)Elements have different electron configurations  different electron configurations mean different levels of bonding  When two or more atoms come together it creates a new substance called a COMPOUND  This just means that the way compounds are formed depends on how many valence electrons an atom has

13. Learning Check A.Number of valence electrons in aluminum. Aluminum is a metal and is found in group 13. It has an atomic number of 13. 1) 1 e - 2) 2 e - 3) 3 e -

14. Learning Check Give the ionic charge for each of the following: A. 12 p + and 10 e - 1) 02) 2+3) 2- B. 50p + and 46 e- 1) 2+2) 4+3) 4- C. 15 p + and 18e- 2) 3+ 2) 3-3) 5-