1. ATOMS TO IONS Why atoms become ions How to draw Lewis Dot Structures
How to determine the charge of an ion

2. Rules for being an atom! Use as little energy as possible Be stable
Give or steal electrons to get a full outer energy level!! (either 2 or 8 electrons)

3. 1. Use as little energy as possibleH He
Electrons stay far apart from each other
Electrons travel in pairs before moving to the next energy level
no more than 4 pairs /energy level (except level 1 has only 1 pair)

4. 2. Be stable = full outer energy levelH He
Level 1: 1 pair max (2 electrons)
Level 2: 4 pairs max (8 electrons)
Level 3: 4 pairs max (8 electrons)

5. 2. Be stable = full outer energy level
1H NOT FULL H
2He
FULL  !! He

6. 3. What about atoms that don’t have full energy levels?
It can give up an electron Or
It can gain 7 electrons Li Li
is REACTIVE Li
Which take “less effort?”

7. Metals GIVE electrons Li Li Metals GIVE electrons Lose an energy level
Make CATIONS
Have a positive charge
is REACTIVE

8. Non-Metals TAKE electronsCl Cl
Non-Metals IONS
TAKE electrons
Have same # energy levels
Make ANIONS
Have negative charge
is REACTIVE

9. LEWIS DOT STRUCTURES
A shorthand way of showing valence electrons

10. Show only the VALENCE ELECTRONS!
LEWIS DOT STRUCTURES
Show only the VALENCE ELECTRONS!

11. X LEWIS DOT STRUCTURES How to draw Lewis Dot:
Write the symbol for the element (the symbol has 4 sides)
Determine the number of valence electrons for the element
Use a dot to represent each electron
Apply dots counterclockwise at 3; 12; 9 and 6:00; (If 2 or less apply at 3 and 9:00)
The number of dots represents the number of valence electrons (7 in this example) X

12. BECOMING AN ION
Easy to see in Lewis dot structure if atom has full energy level
Easy to see charge of ion
Every atom has 0 or 8 electrons in Lewis Dot to become an ion!!
F atom
F ION
Stable for full valence shell also called noble gas electron configuration

13. BECOMING AN ION Li • Atom become ions TO BECOME MORE STABLE
IONS are atoms that have gained or lost electrons to complete their energy levels
Positive ions (cations) are formed when an atom loses electrons.
Negative ions (anions) are formed when an atom gains electrons.
Usually metals form cations & non-metals anions
F atom
F ION
Li •
Li +1
Stable for full valence shell also called noble gas electron configuration

14. CHARGE Always CHARGE = #p - # e-
# of electrons that an atom GIVES or TAKES to have a full valence energy level
example: Chlorine
Needs to take one electron to have a full energy level
CHARGE is NEGATIVE adding an e- gives Cl 18 electrons:
Charge = # p - # e-
17 p – 18 e- = -1 charge

15. GROUPS & CHARGE Charge follows a pattern for the GROUPS
Can you identify the pattern? +1 +2 +3
- 3
- 2
- 1

16. PRACTICE Draw the Lewis Dot for beryllium ION
Draw the Lewis Dot structure for Be atom (#p=4, so #e-=4, but # valence e-=2)
Be has 2 valence electrons, GIVE or TAKE?
Give 2 or take 6
Which is “easier?” - GIVE AWAY 2
Charge = #p – # e (since you gave 2 away) = +2
HELPFUL HINT:
+ = it’s positive/good to give electrons; so give away 2 means +2
- = it’s negative/bad to take/steal electrons; so take 2 means -2

17. - CHARGE +
PRACTICE: Na (atomic #11) and N (Atomic #7) Na
Na+1
N-3 N

18. # electrons gained or lost
To summarize: CHARGE
Acts like
METAL
NON-METAL
INERT
Alkali metals Group I
Alkaline earth metals Group 2
Group 13
Group 14
Group 15
Group 16
Halogens
Group 17
Noble Gases
Group 18
Lewis Dot for atom
Li •
• Be • •
• B •
• C •
• N:
• •
• O •
: F:
: Ne:
Charge on Ion
+ 1
+ 2
+ 3
+ 4
- 4
- 3
- 2
- 1
# electrons gained or lost
1e- lost
2e- lost
3e- lost
4e- lost
4e- gained
3e- gained
2e- gained
1e- gained
No change
Example
X+1
X+2
X+3
X+4
X-4
X-3
X-2
X-1 X
Lewis Dot for ION
[Li] +1
or Li+ Li+
[Be] +2
or Be+2
[B] +3
or B+3
[C] +4
or C+4 Ne -4 C -3 N -2 O -2 O -2 O -2 O -1 F