More on Electrons ! !

Find the electron configuration and draw the orbital diagram for…. Na

Valence Electrons Electrons in the outermost energy shell Ex. Na has 1 valence electron Mg has 2 valence electrons Electrons that are involved in chemical reactions and form chemical bonds with other atoms. Gained or lost by atoms in a reactions ***Except for transition elements, the number of valence electrons for an atom = group number !!!!

Practice: How many valence electrons? 1)Be6) S 2)N7) Ca 3)O8) Sr 4)P9) C 5)Cl10) Br

Octet Rule Main group atoms gain/lose electrons in order to achieve a total of 8 electrons in their outermost electron shell. Therefore, 8 valence electrons = satisfied atom. Noble Gases = full octet, not reactive since they don’t need to gain/lose electrons.

Example 1: Mg What does it have to do to achieve 8 electrons?

Example 2: Cl What is it going to do to achieve 8 electrons?

Lewis Dot Structures Named for G.N. Lewis, who developed the octet rule. Method of representing valence electrons for an atom. Electrons are represented by dots around an element symbol Electrons shown in pairs, any unpaired electrons are available to be gained/lost in a chemical reaction Used to describe chemical bonding.

Example 1: Ne Lewis Dot Structure How many valence electrons???

Example 2: I How many valence electrons?

Example 3: N How many valence electrons?

Example 4: B

Example 5: Mg

Classwork Draw Lewis Dot structure. 1)Li6) H 2)F7) He 3)P8) Cs 4)Be9) O 5)C10) K

Ions Atoms with an electric charge Cation= positively charged atom, losing electrons Anion = negatively charged atom, gaining electrons Polyatomic ions = more than one atom composition, electrically charged (look in your reference table)

Examples Na + H + Mg +2 Cl - Li Ca +2 H Do the PEN method

Monoatomic Ions Ions created from a single atom (ex. Mg +2, Na + ) The charge on these ions can be determined based on the group number. Group I-- +1 charge Group II charge Some exceptions Al +3 N -3 O -2 S -2

Now we move to anions: Group VII charge **These groups readily form ions but some groups do not form ions and others form ions with various charges. **Transition elements vary in the charged ions they can form Ex. Cu, either +1 or +2 Fe, either +2 or +3

Oxidation Numbers Numbers assigned to an atom existing in compound or ion. NOT the same as charges on an ion, do NOT indicate gain/loss of electrons.

Oxidation Number Rules 1) Atoms of pure elements, oxidation # = 0 2) Fluorine (F) –always -1 3) Oxygen(O)—majority of the time -2 4) Hydrogen (H) – mostly has a +1, some exceptions. 5) Monoatomic ion charges = oxidation number **These numbers add to ZERO in a neutral atom!!!

Assign Charges to the following… 1)Ca 6) Na 2)O 7) Br 2 3)F 8) Li 4)O 2 9) H 5)Cl 10) S