Chemical Bonding

Bonding Chapter 7Names of Elements (dont write)The most common source for element names is a property of the elements. EX: nitrogen: Greek for nitron (niter) and genes (to be born). Niter was the name for any naturally occurring substance that contained nitrogen.Some elements get their name from their place of discovery, person of honor, or from the mineral from which they are obtained.

Chemical Symbols (dont write)J. J. Berzelius, a Swedish chemist, is generally given credit for creating the modern symbols for the elements.In some cases, the Latin form of the element was used.EX:Iron is Fe for ferric

Chemical Formulas p56Warm up: why dont some of the symbols match the names of the elements?Formula:a combination of symbols that represents the composition of a compound. Symbols C8H18atoms of each

Types of Bonds p561. Ionic bondTransfer of e- from a metal to a nonmetal forms an ionic compound.EX: Na+ + Cl- NaClIonic compounds are crystal solids with a high melting point.

Types of Bonds p562. Covalent bondsharing of e- between nonmetals resulting in a molecule.EX: H2 + O H2OMolecules have lower melting points and are mostly gases or liquids at room temp.

Types of Bonds p563. Metallic bondshare electrons among many atomsBond Character p56Electrons are transferred when the electronegativity difference is high. They are shared when the difference is lowA difference of 2.0 and higher will produce ionic bonds. 0.4 and below= covalent (sharing)0.41 and 1.99= polar covalent (in between sharing and transferring)

Example p56EX: Magnesium + Oxygen|1.2 3.5| = 2.3 =Ionic

(on periodic table) Bond Character p55Predict the bond character for the following pairs of elements using a CREW statement: (electronegativities on periodic table)B P: |2.0 2.1|=0.1 covalentBr-Cl :|2.8-3.0| = 0.2 covalent Na-F: |0.9 4.0| =3.1 ionic

Valence Electrons: Review

1222345678Lewis Dot Diagrams p58Warm up: What kind of bond will form between Cs and O?Step 1: Write the symbol.Step 2: find number of valence electrons (table)Step 3: Start at the bottom and place dots around symbol clockwise. One at a time, then paired.

Lewis Dot Diagrams p58EX: carbonstep 1: C

step 2: group 4, 4 valence e-

step 3: C

Lewis Dot Diagrams p58EX: brominestep 1: Br

step 2: 7 ve-

step 3: Br

15Do page from red chemDrawing Ionic Bonds p58Draw Lewis dots for each element.

Na + Cl

Draw an arrow to show the e- exchange between atoms.

Drawing Simple Ionic Bonds p58 Now draw them together.

Na Cl

17Do page from red chemExchange of Electrons

Covalent Bonding (ch. 8) p60Warm up: what is the difference between an ionic and covalent bond?We will represent covalet bonding by drawing Lewis Structures.Lewis Structures of Molecules p601. Count the total number of valence e-2. Determine the central atom. Often the unique atom (only one of it), and is usually written first.Or the least electronegative element3. Arrange the other atoms around the central atom.

4. Connect all atoms with one bond (structural formula). 5. Subtract the number of electrons used; two for each bond. 6. Distribute the remaining electrons in pairs around the atoms, satisfy the octet rule. the most electronegative atom gets them first. (Hydrogen only gets 2 electrons!!!)

7. If you run out of electrons, you need to form double or triple bonds. 8. If you have extra electrons, put them on the central atom in pairs (unshared pair). Q. How do you think the lengths and strengths of single, double, and triple bonds compare?

Lewis StructuresEX: AsI31. Count valence e- [5 + (3 x 7)]= 262. Place As (least in number) in center.3. Place the three Iodines around As.4. Draw lines (bonds connecting them) I As I I5. Subtract # used for bonds (26 6) = 20 e-.6. Place e- around the three I atoms first because they are the most electronegative. I As I I7. We did not run out of e- so we do not have any double or triple bonds.8. We have 2 extra e- (20 starting (3x6) = 2. Place them around the central atom.

I As I I

Lewis Structure of CH2O1. Count total valence e-(C=4, H=1x2, O=6)= 12 valence e-2. Place C in the center.3. Place the 2 hydrogens and one oxygen around C.4. Draw lines connecting H and O to C.5. Subtract number of bonded e- from total. (12-6) = 6

6. Place e- around the oxygen atom first because it is the most electronegative. 7. We ran out of e- before carbon satisfied its octet. This means that we will have a double bond between the carbon and oxygen. (Hydrogen cannot form double bonds).8. There will be no unshared e-.

Lewis Structure of CH2OHC O

H

28Do red chemExceptions to the Octet Rule P62Warm up: how do you think the length and strength of a single, double and triple bond compare?Hydrogen only needs 2 ve- Al and B only need 6 ve-Ex) BCl3Elements above atomic number 15 can have more than an octet.Ex) SF4

Lewis Structures of Polyatomic Ions p62Lewis Diagrams for the polyatomic ions is the same, except the difference in charge (+ or -) must be accounted for.Put final structure in brackets

Lewis Structure of ClO31-1. Count valence e-, including charge7 + (3x6) + 1 = 26 total2. Place Cl in the center.3. Arrange the three O around it.4. Draw bonds from O to Cl.5. Subtract e- used in bonds (26 6) = 20 e-.6. Place remaining e- around the three oxygens to satisfy octet.

7. There are two e- left over so we will not have multiple bonds.8. Place the last two e- on the central atom.*For polyatomic ions: place structure in brackets with the charge indicated on outside as demonstrated

1- OCl O

OResonance Structures p62Some molecules and ions cannot be represented by a single Lewis Structure. EX: Ozone O3

O=OO OO=O

Draw a 2-way arrow to show resonance

Resonance of NO2

Shapes of Molecules p64Warm up: whats the difference between 2-dimensional and 3-dimensional?video

VSEPR Theory p64Valence shell, electron-pair repulsion (VSEPR) Theory states that repulsion between valence-level electrons causes them to be as far apart as possible.

VSEPR Theory to Predict Molecular GeometriesStep 1: Write the Lewis Structure for the molecule.Step 2: Represent the central atom in molecule by the letter A.Step 3:Represent the atoms bonded to it by the letter XStep 4: Represent the # of unshared pairs with the letter EStep 5: Now refer to Molecular Structures handout

Ex. AlCl3What are the bond angles?

Ex. PCl3Bond angles?Why do they differ?

Ex. H2ONotice that there are several bond angles why?video

41Vsepr red chemPolar bondsOccur if the electronegativity difference between 2 atoms is high.Electrons are pulled to one end of the bond, making a negative end and positive end (dipole). Ex) H-F An arrow is drawn to show direction electrons pulled. Ex) H-FNonpolar bonds have electrons evenly dispersed. Ex) F-FPolar MoleculesWhen one end of a molecule has a high concentration of electrons and the other has lost them.Ex. H2O, CHCl3 videoNonpolar molecules can have polar bonds but are not polar overall.Ex) CF4 videoLewis Structure of AlCl3EX: AlCl31. Lewis: Al has 3 valence and Cl has 7 x 3 for a total of 24 e-.2. Place Al in center.3. Place Cl around Al.4. Draw bonds connecting Al and Cl.5. Subtract bonds from total e-(24 6) = 18 e-

6. Now put electrons around the most electronegative atoms (Cl) first, try to satisfy octet rule.7. There are no remaining e-. Note: this molecule is an exception to the octet rule because in this case Al only forms three bonds.

Cl

ClAl ClPredicting Molecular Geometry of AlCl31. Refer to structure.2. Al will be represented by letter A.3. Cl will be represented by letter X.4. We have AX3. Refer to Table 1 and look for AX3. 5. According to the Table, the molecular geometry for AlCl3 is Trigonal-planar (aka- equilateral triangle).

Next Example: PCl31. Lewis Structure: Cl

Cl P Cl2. P is represented by A. The unshared pair is represented by E.3. Cl is represented by X. 4. We have AX3E. Refer to Table 3.

Molecular Geometry of H2ORemember, H2O has a Lewis Structure of HOH

The O is represented by A and the two H are represented by X. There are two unshared pairs represented by E2.