ATOMS TO IONSATOMS TO IONS• Why atoms become ions

• How to draw Lewis Dot Structures

• How to determine the charge of an ion

Rules for being an atom!Rules for being an atom!

1. Use as little energy as possible

2. Be stable

3. Give or steal electrons to get a full outer

energy level!! (either 2 or 8 electrons)

1. Use as little energy as possible1. Use as little energy as possible

H

He

• Electrons stay far apart from each otherElectrons stay far apart from each other

• Electrons travel in pairs before moving to the next Electrons travel in pairs before moving to the next energy level energy level

• no more than 4 pairs /energy level (except level 1 no more than 4 pairs /energy level (except level 1 has only 1 pair)has only 1 pair)

2. Be stable = full outer energy level2. Be stable = full outer energy level

H

He

• Level 1: 1 pair max (2 electrons)Level 1: 1 pair max (2 electrons)

• Level 2: 4 pairs max (8 electrons)Level 2: 4 pairs max (8 electrons)

• Level 3: 4 pairs max (8 electrons)Level 3: 4 pairs max (8 electrons)

2. Be stable = full outer energy level2. Be stable = full outer energy level

11HH

NOT FULL NOT FULL

H22HeHe

FULL FULL !! !!

He

3. 3. What about atoms that don’t have What about atoms that don’t have full energy levels?full energy levels?

is REACTIVEis REACTIVE

Li

It can give up an electron

OrIt can gain 7 electrons

Li

LiWhich take “less effort?”

Metals GIVE electronsMetals GIVE electrons

is REACTIVEis REACTIVE

Li

Metals

•GIVE electrons

•Lose an energy level

•Make CATIONS

•Have a positive charge

Li

Non-Metals TAKE electronsNon-Metals TAKE electrons

is REACTIVEis REACTIVENon-Metals IONS

•TAKE electrons

•Have same # energy levels

•Make ANIONS

•Have negative charge

Cl Cl

LEWIS DOT STRUCTURESLEWIS DOT STRUCTURES

A shorthand way of showing valence electrons

LEWIS DOT STRUCTURESLEWIS DOT STRUCTURES

Show only the VALENCE ELECTRONS!

LEWIS DOT STRUCTURESLEWIS DOT STRUCTURES

How to draw Lewis Dot:

1. Write the symbol for the element (the symbol has 4 sides)

2. Determine the number of valence electrons for the element

3. Use a dot to represent each electron

4. Apply dots counterclockwise at 3; 12; 9 and 6:00; (If 2 or less apply at 3 and 9:00)

5. The number of dots represents the number of valence electrons (7 in this example)

X

• 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!!

BECOMING AN ION

F atom F ION

• 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

BECOMING AN ION

Li • Li +1

F atom F ION

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 levelNeeds to take one electron to have a full energy level

CHARGE is NEGATIVECHARGE is NEGATIVE adding an e- gives Cl 18 electrons: adding an e- gives Cl 18 electrons:

Charge = # p - # e- Charge = # p - # e-

17 p – 18 e- = -1 charge17 p – 18 e- = -1 charge

CHARGE

GROUPS & CHARGECharge follows a pattern for the GROUPSCan you identify the pattern?

+1

+2 +3 - 3 - 2 - 1

0

PRACTICE Draw the Lewis Dot for beryllium ION

1. Draw the Lewis Dot structure for Be atom (#p=4, so #e-=4, but # valence e-=2)

2. Be has 2 valence electrons, GIVE or TAKE? Give 2 or take 6 Which is “easier?” - GIVE AWAY 2 Charge = #p – # e-

4 - 2 (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

- CHARGE +

Na Na+1

N N-3

PRACTICE: Na (atomic #11) and N (Atomic #7)

To summarize: CHARGETo summarize: CHARGEActs like METAL NON-METAL INERT

Alkali metals

Group I

Alkaline earth metals Group 2

Group 13 Group 14 Group 14 Group 15 Group 16 HalogensGroup 17

Noble Gases

Group 18

Lewis Dot for atom Li • • Be •

•• B •

•• C •

•

•• C •

•

•• N:

•

• •• O •• •

• •: F:•

• •: Ne:• •

Charge on Ion + 1 + 2 + 3 + 4 - 4 - 3 - 2 - 1 0

# electrons gained or

lost1e- 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 -1

F -2

O -2

O -2

O