Chemistry SM-1131 Lesson 1

Chemistry SM-1131Week 14 Lesson 1Dr. Jesse ReichAssistant Professor of ChemistryMassachusetts Maritime AcademyFall 2008

1Class TodayPoemReview: valence electrons, octet rule, OrbitalsLewis Dot StructureSingle, Double, Triple BondsThere is class on Friday!2P orbitals

3D orbitals

4F orbitals

5Simple RuleWhen you go from a lower energy shell to a higher energy shell the shapes of the orbitals dont change, but they do get bigger. This is because they are physically moving further away from the nucleus (most of the time).6RulesAufbau- 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.Hunds 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.7Energy1s2s3s4s5s2p2p2p3p3p3p4p4p4p3d3d3d3d3d4d4d4d4d4dOrbital Energy DiagramStart 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.8Electron ConfigurationIt 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.9Energy1s2s3s4s5s2p2p2p3p3p3p4p4p4p3d3d3d3d3d4d4d4d4d4dOrbital Energy Diagram of KrKr 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 1s22s22p63s23p64s23d104p6.10Electron configuration patternKr = 1s22s22p63s23p64s23d104p6.Ar = 1s22s22p63s23p6.Ne = 1s22s22p6.He = 1s2Notice how the earlier ones keep showing up in the later ones. Thats part of the pattern, and it gives us a short cut.11Noble Gas ConfigurationKr = 1s22s22p63s23p64s23d104p6.Ar = 1s22s22p63s23p6.Ne = 1s22s22p6.He = 1s2Instead of writing the full noble gas configuration its common just to write [He], [Ne], [Ar], or [Kr], and everyone knows youre talking about the noble gas configuration of those elements.

12Energy1s2s3s4s5s2p2p2p3p3p3p4p4p4p3d3d3d3d3d4d4d4d4d4dOrbital Energy Diagram of SrRemember, Kr has the following configuration: 1s22s22p63s23p64s23d104p6. Now were just going to piggy back on that and say we also have a 5s2 now too, or [Kr]5s2. You can see how its a lot shorter to write electron configurations using the noble gas configurations the bigger the atom gets.13Core and valence electronsCore 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.

14Block Pattern

15Noble gases are specialNoble gas dont 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).16Now, consider chargesRemember our previous chart I told you to just memorize. Lets think about this another way.Group 1 = +1Group 2 = +2Group 13 = +3Group 14 =+ or 4Group 15 = -3Group 16 =-2Group 17 = -1Group 18 = 0 17Shielding and periodic trendsShielding is a tricky concept, but not horrendous. Fill out this packet over break. Use graph paper. Its worth 10 points, so dont slough off and for the first time youll lose 5 points on the test if you dont complete it. This one is that important. IT IS DUE WEDNESDAY! Well talk about the results when you get back.

18Energy1s2s3s4s5s2p2p2p3p3p3p4p4p4p3d3d3d3d3d4d4d4d4d4dOrbital Energy Diagram19Mini ReviewValence 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 electronsOctet 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 electrons20Lewis Dot StructureG. 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. 21Lewis Dot Structure1- 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.22

Lewis Dot Theory

23IonsSo Lithium has 1 valence Electron. If it loses that electron it has a +1 charge and 0 valence electrons. Wed write it like this: Li+ and the Lewis Dot would be this:

Li24IonsOxygen has 6 valence electrons. It wants eight. So, typically it gains two electrons. Well write it like O2-, and its dot structure would be the following. O25Ionic CompoundsLi +1 O -2Li2O

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?26Li2O Li O Li27Ionic CompoundsMgOMg+2O-2Mg2O2MgO

Mg O

Mg has 0 VE and O has 8 VE. Octet Rule!28In ClassI want you to draw Lewis Dot Structures for NaCl, MgCl2, AlCl3, and Na2O29BondsOk, Ive told you HINClBrOF is so unstable that they are all diatomic. Lets start looking at those.30H2H has 1 valence electron. It wants either 0 or 2. So far, weve seen it give or take an electron to get to 0 or 2 valence electrons. This time its going to do something different. Its going to share.

H H we draw it this like: H H31I2H has 1 valence electron. It wants either 0 or 2. So far, weve seen it give or take an electron to get to 0 or 2 valence electrons. This time its going to do something different. Its going to share.

I I we draw it this like: I I I - I 32Bonds have 2 electronsBecause 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 electronsI-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 33NClBrOFFor 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?34StuffClass Wednesday and FridayTest Wed of next week.35