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) Be 6) S

2) N 7) Ca

3) O 8) Sr

4) P 9) C

5) Cl 10) 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

ClassworkDraw Lewis Dot structure.

1) Li 6) H

2) F 7) He

3) P 8) Cs

4) Be 9) O

5) C 10) 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 IonsIons 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 chargeGroup II -- +2 charge

Some exceptions Al +3

N-3

O-2

S-2

Now we move to anions:Group VII-------- -1 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 formEx. 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) Br2

3) F 8) Li

4) O2 9) H

5) Cl 10) S