Valence Electrons, Ions, and the Periodic Table

Valence Electrons

•Valence electrons are electrons in the outer energy level of an atom.

Practice!

• Find the number of valence electrons for:1.Li2.P3.I4.Ar5.Ca6.O7. He

Check It!

1. Li = 12. P = 53. I = 74. Ar = 85. Ca = 26. O = 67.. He = 2 (not 8)!

Now For Lewis Dot Structures!(Also called Electron Dot Structures)

•Step 1: Write the symbol for the element.•Step 2: Put ‘dots’ around the symbol to represent valence electrons.

See It In Action!

•Let’s do Carbon. The symbol for carbon is C•Carbon is in Group 4 •4 valance electrons•Put one on each side!

You do some!

• Draw the Lewis Dot Structures for the following atoms:

1.Oxygen2.Sodium3.Fluorine4.Nitrogen5.Beryllium

Checkit!1. 2. 3.

4. 5.

AcrossPeriod2

Electron Dot, or Lewis Dot Symbols for the “Representative” Elements

Since elements in the same family have the same number of valence electrons, their dot structures will look the same, too!

ION: an atom that has gained or lost one or more electrons

**atoms with the same atomic number (protons), but different number of electrons

§An atom that has LOST one or more electrons (has an overall positive charge)

11 Protons8 Neutrons

Na1911

Na1911

11 Protons8 Neutrons

Na1911

+1Na

+1

11 Protons8 Neutrons

Na1911

+1

+1Na Sodium Ion

11 Protons8 Neutrons

If a neutral Magnesium atom loses two electrons, what will its overall charge be?A. -2B. +1C. +2D. -1C

How many electrons are in an ion of K +1 ?A. 39B. 18C. 19D. 20

B

§An atom that has gained one or more electrons (has an overall negative charge).

9 Protons8 Neutrons

F179

F179

9 Protons8 Neutrons

F179

-1

F -1

9 Protons8 Neutrons

F179

-1

F -1Fluoride Ion

9 Protons8 Neutrons

If a neutral oxygen atom gains two electrons, what will its overall charge be?A. -2B. +1C. +2D. -1 A

How many electrons are in an ion of Br -1 ?A. 35B. 34C. 36D. 79 C

Learning Check

Give the ionic charge for each of the following:1. 12 p+ and 10 e-

A) 0 B) 2+ C) 2-

2. 50 p+ and 46 e-A) 2+ B) 4+ C) 4-

3. 15 p+ and 18e-A) 3+ B) 3- C) 5-

Now What Do I Do With That?

• We can use number of valence electrons to predict which charge they make when we turn them into an ion.

• Review: what’s an ion??–An atom that has gained or lost electrons.

• Atoms can become more stable if they have FULL outer energy levels

PREDICTING ION CHARGES

In general

•metals (like Mg) lose electrons ---> cations

•nonmetals (like F) gain electrons ---> anions

How So?

• For atoms with LESS than 4 valence electrons, they’re going to lose/give up electrons to form positive cations.

• For atoms with MORE than 4 valence electrons, they’re going to gain/steal electrons to form negative anions.

• For atoms with 4 valence electrons, it can go either way.

• For atoms with 8 valence electrons, there is no change.

Example

• I need to know what ion Aluminum forms.• I know that it has 3 valence electrons.• Is 3 closer to 0 or 8?• So will it gain or lose electrons?• How many will it lose to be 0?• If it loses electrons, will it be + or -?• So I end up with…

Al+3

Closer to 0

Lose

+

All 3

More Practice!

• Predict the ion formed by the following elements: Write the symbol with the charge.

1.Cl2.B3.K4.Ca5.O6.Ne

Check It!

1.Cl = Cl-

2.B = B+3

3.K = K+

4.Ca = Ca+2

5.O = O-2

6.Ne = Ne (no change)

1 2 3 4 5 6 7

Ion Formation SummarynAtoms gain or lose electrons to become more stable.

–They achieve the same number of valence electrons as the Noble Gases (in the last column)