more on electrons ! !. find the electron configuration and draw the orbital diagram for…. na
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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
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