Electron Configuration, Ion Formation, and Lew Structures

Vocabulary:1. valence shell2. valence electrons3. anion4. cation5. isoelectric6. Lewis structure

(Lewis dot diagram)

Banksy, British, 2002

Pauling Electronegativities Linus Pauling

developed the concept of electronegativity and assigned values to atoms to quantify electronegativity.

Electronegativities have no units; they are comparative only.

Draw the orbital diagram for chlorine

4s __ 4p ___ ___ ___

3s ___3p ___ ___ ___

2s ___2p ___ ___ ___

1s ___

17 protons

potassium

4s __ 4p ___ ___ ___

3s ___3p ___ ___ ___

2s ___2p ___ ___ ___

1s ___

19 protons

Identify the valence electronschlorine

4s __ 4p ___ ___ ___

3s ___3p ___ ___ ___

2s ___2p ___ ___ ___

1s ___

17 protons

potassium

4s __ 4p ___ ___ ___

3s ___3p ___ ___ ___

2s ___2p ___ ___ ___

1s ___

19 protons

Consequences

chlorine

4s __ 4p ___ ___ ___

3s ___3p ___ ___ ___

2s ___2p ___ ___ ___

1s ___

17 protons

potassium

4s __ 4p ___ ___ ___

3s ___3p ___ ___ ___

2s ___2p ___ ___ ___

1s ___

19 protonsOnly 2 more protons

But a whole new energy level

Consequences

chlorine

4s __ 4p ___ ___ ___

3s ___3p ___ ___ ___

2s ___2p ___ ___ ___

1s ___

17 protons

potassium

4s __ 4p ___ ___ ___

3s ___3p ___ ___ ___

2s ___2p ___ ___ ___

1s ___

19 protons

That means strong attraction for these valence electrons (large Zeff).

And weak attraction for this valence electron (low Zeff).

Consequences

chlorine

4s __ 4p ___ ___ ___

3s ___3p ___ ___ ___

2s ___2p ___ ___ ___

1s ___

17 protons

potassium

4s __ 4p ___ ___ ___

3s ___3p ___ ___ ___

2s ___2p ___ ___ ___

1s ___

19 protons

That means easy to gain 1 more electron here (high electronegativity)

And easy to lose an electron here (low ionization energy)

Summary:

Elements that have a nearly full valence shell, like chlorine, have high electronegativities and can gain electrons easily.

chlorine

4s __ 4p ___ ___ ___

3s___3p ___ ___ ___

2s___2p ___ ___ ___

1s ___

17 protons and 17 electrons = 0 charge

Summary:

Elements that have a nearly full valence shell, like chlorine, have high electronegativities and can gain electrons easily.

chlorine

4s __ 4p ___ ___ ___

3s___3p ___ ___ ___

2s___2p ___ ___ ___

1s ___

17 protons and 18 electrons = 1- charge

Summary:

Atoms that have gained one or more electrons are now negative ions and are called anions (ˈan-ī-ən).

chlorine

4s __ 4p ___ ___ ___

3s___3p ___ ___ ___

2s___2p ___ ___ ___

1s ___

17 protons and 18 electrons = 1- charge

potassium

4s __ 4p ___ ___ ___

3s___3p ___ ___ ___

2s___2p ___ ___ ___

1s ___

19 protons + 19 electrons = 0 charge

Summary:

Elements that have a nearly empty valence shell, like potassium, have low electronegativities and can lose electrons easily.

potassium

4s __ 4p ___ ___ ___

3s___3p ___ ___ ___

2s___2p ___ ___ ___

1s ___

19 protons + 18 electrons = 1+ charge

Summary:

Atoms that have lost one or more electrons are now positive ions and are called cations (kat-ī-ən).

Noticechlorine anion (1- charge)

4s __ 4p ___ ___ ___

3s___3p ___ ___ ___

2s___2p ___ ___ ___

1s ___

potassium cation (1+ charge)

4s __ 4p ___ ___ ___

3s___3p ___ ___ ___

2s___2p ___ ___ ___

1s ___When each atom gained or lost electrons, the new outer shell (energy level) is full, like the noble gases.

Notice

Different atoms or ions that have the same electron configuration are called isoelectric. The Cl- ion is isoelectric with the K+ ion. They are both isoelectric with neon.

chlorine anion (1- charge)

4s __ 4p ___ ___ ___

3s___3p ___ ___ ___

2s___2p ___ ___ ___

1s ___

potassium cation (1+ charge)

4s __ 4p ___ ___ ___

3s___3p ___ ___ ___

2s___2p ___ ___ ___

1s ___

The Octet Rule

Atoms lose or gain electrons in order to have a full valence shell (a noble gas configuration). This will typically result in 8 valence electrons and make the resulting ion isoelectric with the noble gas.

An easier way!Rather than draw orbital diagrams, we can use Lewis Structures

(Lewis Dot Diagrams) to show numbers of valence electrons.

Cl

1. Write symbol of element.

2. Determine number of valence electrons by position on periodic table

3. Use dots to represent electrons around symbol (one at a time on each side and then pair them up.)

7 valence electrons because in group 17

An easier way!

Cl

So when chlorine forms an ion, will it gain or lose electrons? How many?

It needs one more to have an octet.

What will its charge be now?

1-

Lewis Structure Practice: potassium

K

1. Write symbol of element.

2. Determine number of valence electrons by position on periodic table

3. Use dots to represent electrons around symbol (one at a time on each side and then pair them up.)

1 valence electrons because in group 1

Lewis Structure Practice: potassium

K

So when potassium forms an ion, will it gain or lose electrons? How many?

It will lose one electron to have a full valence

What will its charge be now?

1+

Lewis Structure Practice: nitrogen

N

1. Write symbol of element.

2. Determine number of valence electrons by position on periodic table

3. Use dots to represent electrons around symbol (one at a time on each side and then pair them up.)

5 valence electrons because in group 15

Lewis Structure Practice: nitrogenSo when nitrogen forms an ion, will it gain or lose electrons? How many?

It will gain three electrons to have a full

valence

What will its charge be now?

3-

N

Short Cut

Using periodic trends, we can predict the ion charge for the main group elements.1+

2+

3+ 4+/-

3- 2- 1- 0