Chemistry SM-1131Week 14 Lesson 1

Dr. Jesse ReichAssistant Professor of Chemistry

Massachusetts Maritime AcademyFall 2008

Class Today• Poem• Review: valence electrons, octet rule, Orbitals• Lewis Dot Structure• Single, Double, Triple Bonds• There is class on Friday!

P orbitals

D orbitals

F orbitals

Simple Rule

• When you go from a lower energy shell to a higher energy shell the shapes of the orbitals don’t change, but they do get bigger. This is because they are physically moving further away from the nucleus (most of the time).

Rules• Aufbau- The building up rule. Start at the lowest energy

orbital (look at the chart) and start filling up there.• The Pauli exclusion principle- No two electrons can have

the same set of four quantum numbers. Therefore you can only have a max of 2 electrons in any given orbital and they have to have different spins.

• Hund’s Rule- Electrons are negative and repel each other, so if you put electrons into p, d, or f orbitals spread them out so they are all spin up first, and then go back and pair them.

Energy

1s

2s

3s

4s

5s

2p 2p 2p

3p 3p 3p

4p 4p 4p3d 3d 3d 3d 3d

4d 4d 4d 4d 4d

Orbital Energy Diagram

Start by filling up the 1s, then the 2s and then the 2ps. Continue from there based on which set of orbitals is closest to the bottom of the chart.

Electron Configuration

• It takes a long time and uses a lot of space when chemists have to write a huge orbital energy diagram. Chemists came up with a way to shrink this down. The short hand notation is called electron configuration.

• To write the short hand list the electrons in the atom starting with the lowest, and then moving up from there.

Energy

1s

2s

3s

4s

5s

2p 2p 2p

3p 3p 3p

4p 4p 4p3d 3d 3d 3d 3d

4d 4d 4d 4d 4d

Orbital Energy Diagram of Kr

Kr has a total of 36 electrons. There are 2 in the 1s orbital, 2 in the 2s orbital, 6 in the 2p orbitals, 2 in the 3s, 6 in the 3p orbitals, 2 in the 4s, 10 in the 3d, and 6 in the 4p. We will write this as 1s22s22p63s23p64s23d104p6.

Electron configuration pattern

• Kr = 1s22s22p63s23p64s23d104p6.• Ar = 1s22s22p63s23p6.• Ne = 1s22s22p6.• He = 1s2

Notice how the earlier ones keep showing up in the later ones. That’s part of the pattern, and it gives us a short cut.

Noble Gas Configuration

• Kr = 1s22s22p63s23p64s23d104p6.• Ar = 1s22s22p63s23p6.• Ne = 1s22s22p6.• He = 1s2

• Instead of writing the full noble gas configuration it’s common just to write [He], [Ne], [Ar], or [Kr], and everyone knows you’re talking about the noble gas configuration of those elements.

Energy

1s

2s

3s

4s

5s

2p 2p 2p

3p 3p 3p

4p 4p 4p3d 3d 3d 3d 3d

4d 4d 4d 4d 4d

Orbital Energy Diagram of Sr

Remember, Kr has the following configuration: 1s22s22p63s23p64s23d104p6. Now we’re just going to piggy back on that and say we also have a 5s2 now too, or [Kr]5s2. You can see how it’s a lot shorter to write electron configurations using the noble gas configurations the bigger the atom gets.

Core and valence electrons

• Core electrons are any of the electrons not in the highest shell number. These normally are the same electrons as in the noble gas configuration.

• Valence electrons are the electrons in the highest shell.

Block Pattern

Noble gases are special• Noble gas don’t bond with anything.• Noble gases are incredibly stable.• All noble gases have 8 electrons (except helium

which has 2).• There is something magical about having 8 valence

electrons (or 2 if you are helium).• Chemists call this the octet rule. In short it means

you either want 0 valence electrons or all 8 because either way you look like a noble gas (except helium which only wants 2).

Now, consider charges• Remember our previous chart I told you to just

memorize. Let’s think about this another way.• Group 1 = +1• Group 2 = +2• Group 13 = +3• Group 14 =+ or – 4• Group 15 = -3• Group 16 =-2• Group 17 = -1

• Group 18 = 0

Shielding and periodic trends

• Shielding is a tricky concept, but not horrendous. Fill out this packet over break. Use graph paper. It’s worth 10 points, so don’t slough off and for the first time you’ll lose 5 points on the test if you don’t complete it. This one is that important. IT IS DUE WEDNESDAY! We’ll talk about the results when you get back.

Energy

1s

2s

3s

4s

5s

2p 2p 2p

3p 3p 3p

4p 4p 4p3d 3d 3d 3d 3d

4d 4d 4d 4d 4d

Orbital Energy Diagram

Mini Review

• Valence electrons for the main group elements (1,2, 13-18) are the counted by adding the highest shell S electrons and the highest shell P electrons

• Octet Rule: elements want either 0 or 8 valence electrons. Hydrogen and helium are exceptions. H wants either 0 or 2 valence eletrons. He wants 2 valence electrons

Lewis Dot Structure

• G. N. Lewis (1875-1946) came up with a way to quickly and pictorially show how many electrons an element has. We now call it the Lewis Dot Structure.

Lewis Dot Structure• 1- figure out how many valence electrons it has

(Group 1 =1 ve, Group 2 =2ve, Group 13= 3ve, Group 14= 4ve, Group 15 = 5ve, Group 16 =6ve, Group 17 =7ve, Group 18 = 8ve)

• 2- For every VALENCE electron an element has draw a dot around it. Start by putting 1 dot to the N, S, E, W and then put a second dot in the N, S, E, W.

• 3- A pair of electrons is called a lone pair.• 4- A Single electron is called unpaired.

Lewis Dot Theory

Ions

• So Lithium has 1 valence Electron. If it loses that electron it has a +1 charge and 0 valence electrons. We’d write it like this: Li+ and the Lewis Dot would be this:

Li

Ions

• Oxygen has 6 valence electrons. It wants eight. So, typically it gains two electrons. We’ll write it like O2-, and it’s dot structure would be the following.

O

Ionic Compounds

Li +1 O -2

Li2O

Li O Li

What happens if the two Li each lose 1 electron?How many VE will each Li have? The O?Is the Octet Rule satisfied?

Li2O

Li O Li

Ionic Compounds

• MgO• Mg+2O-2

• Mg2O2

• MgO

Mg O

Mg has 0 VE and O has 8 VE. Octet Rule!

In Class

• I want you to draw Lewis Dot Structures for NaCl, MgCl2, AlCl3, and Na2O

Bonds

• Ok, I’ve told you HINClBrOF is so unstable that they are all diatomic. Let’s start looking at those.

H2

• H has 1 valence electron. It wants either 0 or 2. So far, we’ve seen it give or take an electron to get to 0 or 2 valence electrons. This time it’s going to do something different. It’s going to share.

H H we draw it this like: H H

I2

• H has 1 valence electron. It wants either 0 or 2. So far, we’ve seen it give or take an electron to get to 0 or 2 valence electrons. This time it’s going to do something different. It’s going to share.

I I we draw it this like: I – I I - I

Bonds have 2 electrons

• Because they share electrons when we count how many electrons each one has we say both get the benefit of the two electrons in the bond.

• H-H each one has 2 electrons• I-I each one has 8 electrons, each I has 3 lone

pairs for 6 electrons, and then we say each one has 2 electrons from the shared bond

NClBrOF• For the rest of class put together the diatomic

molecules for the elements listed above. N and O will need more than 1 bond to make the product. O will need 2, and N will need 3.

• Start by writing the Lewis dot structure. As you put electrons around the element add them first so that the lone pair forms away from the adjacent element. Then put an additional electron on top, and then bottom.

• Does every atom has 8 valence electrons?

Stuff

• Class Wednesday and Friday• Test Wed of next week.