Chemistry SM-1131Week 11 Lesson 1

Dr. Jesse ReichAssistant Professor of Chemistry

Massachusetts Maritime AcademyFall 2008

Class Today• Poem• Enjoy you’re break, which starts after classes on

Tuesday through the weekend• Electron Configuration• Noble Gas configurations• Valence electrons• Periodic Blocks• Atomic Trends: Size, Ionization energy, Metallic

Character,

Poem

• Advice from my brother:

“When given a choice between two or more options of how to solve a problem or a difficult situation the hardest choice for you is normally the right path to follow.”

Bohr

• 1 Quantum # and it’s energy shell

Quantum Model

• 4 Quantum models• 1- Energy Shell• 2- Shape• 3- Orientation• 4- Electron Spin

S Orbitals

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.

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 He

He has the atomic number 2. It must have two protons, which means to be neutral overall it needs 2 electrons. They will both go in the 1s orbital. We’ll put the first electron spin up and the second spin down. Arrows are usually drawn as only half arrows, but PowerPoint can’t do that.

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 Ne

Ne has a total of 10 electrons. The first two will go in the 1s, then the next two in the 2s, the next three will be spin up in the 2p, and then the last three will be spin down in the 2p.

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 Ar

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

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 XX

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 He

He only has 2 electrons. They are in the 1s orbital and there are two of them, so the electron configuration is 1s2

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 Ne

Ne has a total of 10 electrons. There are 2 in the 1s orbital, 2 in the 2s orbital, and 6 in the 2p orbitals. We will write this as 1s22s22p6.

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 Ar

Ar has a total of 18 electrons. There are 2 in the 1s orbital, 2 in the 2s orbital, 6 in the 2p orbitals, 2 in the 3s, and 6 in the 3p orbitals. We will write this as 1s22s22p63s23p6.

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

Ar 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.

Noble gas configuration

• That means that anything in period two can be written as [He] plus whatever came after it. Take a look at nitrogen:

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 N

We can also write nitrogen as [He]2s22p6.

Electron Configuration

• The noble gas configuration didn’t save me a lot of work there, but it sure would for Sr atomic number 38.

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.

Periodic Blocks and valence electrons

• Ok, think about the noble gas configuration model, and just write the electrons outside of the core configurations for every member of group 1 and 2 elements on the periodic table I give you.

• Ok, now do that for group 3 and group 4.• Ok, now do that for group 13 and 14.• Ok, now do that for the first two groups of the

lanthanides and actinides.

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

Group 1, 2, and 13

• Group 1 has 1 valence electron and wants to get to 0 or 8. So it will lose one electron and gain a +1 charge.

• Group 2 has 2 valence electrons and wants to get to 0 or 8. So it will lose two electrons and gain a +2 charge.

• Group 13 has 3 valence electrons and wants to get to 0 or 8. So it will lose three electrons and gain a +3 charge.

Group 14

• Group 14 has 4 valence electrons and wants to get to 0 or 8. It can either gain or lose 4 electrons. If it gains 4 electrons it has a -4 charge and 8 valence electrons. If it loses 4 electrons is has a +4 charge and 0 valence electrons.

Group 15, 16, and 17

• Group 15 has 5 valence electrons and wants to get to 0 or 8. It will gain 3 electrons and have a -3 charge.

• Group 16 has 6 valence electrons and wants to get to 0 or 8. It will gain 2 electrons and have a -2 charge.

• Group 17 has 7 valence electrons and wants to get to 0 or 8. It will gain 1 electron and have a -1 charge.

Group 18

• Group 18 has 8 valence electrons and wants to get to 0 or 8. It already has 8 so it won’t gain or lose any electrons.

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. 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 of XX

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 XX

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