Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

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Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3

Transcript of Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Page 1: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Molecular Nomenclature and Geometry

Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3

Page 2: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Covalent Bonding

• Covalent bonding entails a sharing of electrons.

• Covalent bonding usually occurs between nonmetals.

• Form individual molecules.

• Shapes of molecules determines properties.

Page 3: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Properties of Covalent Molecules

• Gases, liquids, or solids (made of molecules)

• Low melting and boiling points

• Poor electrical conductors in all phases

• Many soluble in nonpolar liquids but not in water

Page 4: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Covalent Bonds– attain the octet or full valence by sharing pairs of valence electrons.

Page 5: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Covalent Bonds• For every pair of electrons shared between

two atoms, a single covalent bond is formed. 

• Some atoms can share multiple pairs of electrons, forming multiple covalent bonds. 

Page 6: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Building a Dot StructureBuilding a Dot StructureHydrogen - H2

1. How many valence electrons? (1)

2. Add up the number of valence electrons that can be used.

H = 1 and H = 1

Total = (1 + 1) = 2

= 2 electrons

3. Put dots together

With dots- H:H Electrons

Page 7: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Building a Dot StructureBuilding a Dot StructureHydrogen - H2

With dots- H:H

4. When two dots are together,

replace with a line.

H:H H-H

Electrons

Page 8: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Building a Dot StructureBuilding a Dot StructureAmmonia, NH3

1. Number of Valence electrons H= 1 N=5

Decide on the central atom; never H.

2. Add up the number of valence electrons that can be used.

H = 1 and N = 5

Total = (3 x 1) + 5

= 8 electrons / 4 pairs

Page 9: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

3. Form a single bond between the central atom and each surrounding atom (each bond takes 2 electrons!)

Building a Dot Building a Dot StructureStructure

4.4. Remaining electrons Remaining electrons form LONE PAIRS to form LONE PAIRS to complete the octet as complete the octet as needed (or duet in the case needed (or duet in the case of H).of H). 3 BOND PAIRS and 1 LONE 3 BOND PAIRS and 1 LONE

PAIR.PAIR.

..

Page 10: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

5. Check to make sure there are 8 electrons around each atom except H. H should only have 2 electrons. This includes SHARED pairs.

Building a Dot Building a Dot StructureStructure

6. 6. Also, check the number of electrons in your Also, check the number of electrons in your drawing with the number of electrons from step drawing with the number of electrons from step 2. If you have more electrons in the drawing 2. If you have more electrons in the drawing than in step 2, you must make double or triple than in step 2, you must make double or triple bonds. If you have less electrons in the drawing bonds. If you have less electrons in the drawing than in step 2, you made a mistake!than in step 2, you made a mistake!

..

Page 11: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

H

CH H

H

methane

Carbon has 4 valence electrons

C

H

H

H

H

H C

Ne

Neon

Stable Octet required

Simplest Organic molecule

The H’s can be replaced with any group 17 Halogen(s) to make a multitude of molecular

compounds

Page 12: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

• Diatomic Elements - There are seven elements that exist as diatomic molecules in which two atoms of the same element bond together.

• They are bromine, iodine, nitrogen, chlorine, hydrogen, oxygen, and fluorine. If the symbols are written for these elements in the order given, they spell out Br I N Cl H O F.

• Whenever these elements appear as free elements (by themselves) in a chemical equation, they MUST have a subscript "2"

• Ex. Br2 I2 N2 Cl2 H2 O2 F2

Page 13: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Double Covalent Bond

• Oxygen (which has six valence electrons) needs two electrons to complete its valence shell. Two oxygen atoms form the compound O2, they share two pairs of electrons, forming two covalent bonds (double bond).  

Page 14: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Triple Covalent Bonds

• Nitrogen (which has five valence electrons) needs three electrons to complete its valence shell. Two nitrogen atoms form the compound N2, they share three pairs of electrons, forming three covalent bonds (triple bond). 

Page 15: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Covalent Bonds – Draw the Lewis structures for each atom,

draw circles to show the electrons that are shared, and then write the bond structure and chemical formula.

(A)Fluorine + Fluorine

(B) 3 Hydrogen + 1 Phosphorus

(C) 2 Hydrogen + 1 Sulfur

(D) 1 Carbon + 2 Oxygen

Page 16: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

C(6) - 1s2, 2s2, 2px1, 2py

1, 2pz0

lowest energy state- allows four bonds by electron promotion

Hybridization

C(6) - 1s2, 2s1, 2px1, 2py

1, 2pz1

Excited state

4 valence e-/sp3

2s 2px2py 2pz

+ + +

4 X sp3

Page 17: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

VSEPR

• VSEPR stands for Valence Shell Electron Pair Repulsion.  

• Basically, the idea is that covalent bonds and lone pair electrons like to stay as far apart from each other as possible under all conditions. 

• This is because covalent bonds consist of electrons, and electrons don't like to hang around next to each other much because they have the same charge (like charges repel).

Page 18: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

VSEPR explains why molecules have their shapes. 

• If carbon has four atoms stuck to it (as in CH4), these four atoms want to get as far away from each other as they can.  This isn't because the atoms necessarily hate each other, it's because the electrons in the bonds “hate” each other.  That's the idea behind VSEPR.

Page 19: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Methane is Tetrahedral

109.50

Sp3 hybridized carbon 4 equivalent C-H bonds (bonds)

All purely single bonds are called bonds

H

CH

HH

Page 20: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Molecular Geometry

Page 21: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Polarity

• Depending on the percent covalent vs. ionic characteristic of the bond, molecular compounds can have polar covalent or nonpolar covalent bonds

• The higher the percentage of ionic characteristic the more polar the bond will be

Page 22: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Naming Covalent Compounds

Covalent compounds are named by adding prefixes to the element names.

A prefix is added to the name of the first element in the formula if more than one atom of it is present. (The less electronegative element is typically written first.)

A prefix is always added to the name of the second element in the formula. The second element will use the form of its name ending in ‘ide’.

Page 23: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Naming Covalent Compounds

Prefixes

Subscript Prefix

1 mono-

2 di-

3 tri-

4 tetra-

5 penta-

Subscript Prefix

6 hexa-

7 hepta-

8 octa-

9 nona-

10 deca-

Note: When a prefix ending in ‘o’ or ‘a’ is added to ‘oxide’, the final vowel in the prefix is dropped.

Page 24: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Naming Binary Covalent Compounds: Examples

N2S4 dinitrogen tetrasulfide

NI3 nitrogen triodide

XeF6 xenon hexafluoride

CCl4 carbon tetrachloride

P2O5 diphosphorus pentoxide

SO3 sulfur trioxide

1 mono

2 di

3 tri

4 tetra

5 penta

6 hexa

7 hepta

8 octa

9 nona

10 deca

* Second element in ‘ide’ from

* Drop –a & -o before ‘oxide’

Page 25: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Writing Formulas for Covalent Compounds

The names of covalent compounds contain prefixes that indicate the number of atoms of each element

present.

If no prefix is present on the name of the first element, there is only one atom of that element in the formula (its subscript will be 1).

A prefix will always be present on the name of the second element. The second element will use the form of its name ending in “ide”

Page 26: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Writing Formulas for Binary Covalent Compounds: Examples

nitrogen dioxide NO2

diphosphorus pentoxide P2O5

xenon tetrafluoride XeF4

sulfur hexafluoride SF6

1 mono

2 di

3 tri

4 tetra

5 penta

6 hexa

7 hepta

8 octa

9 nona

10 deca

* Second element in ‘ide’ from

* Drop –a & -o before ‘oxide’

Page 27: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

• Within molecules, covalent bonding holds molecule together

• Between molecules, intermolecular forces hold molecules together to make them liquids or solids.

• Molecules are held in place by intermolecular forces

• Properties– Low to moderate melting point

and boiling point– Soft– Non conductive

Molecular SolidMolecular Solid

Page 28: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Intermolecular ForcesIntermolecular Forces

Intermolecular Forces are Intermolecular Forces are electrostatic forces of electrostatic forces of attraction that exist attraction that exist betweenbetween an area of negative charge an area of negative charge on on one molecule andone molecule and an area an area of positive charge on of positive charge on a a second molecule.second molecule.

Page 29: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

TYPES OF INTERMOLECULAR FORCESTYPES OF INTERMOLECULAR FORCES(only attractions not bonds)(only attractions not bonds)

1.1. Hydrogen Bonding ( generally the Hydrogen Bonding ( generally the STRONGEST)STRONGEST)

2.2. Van Der WaalsVan Der Waalsa. Dipole-dipole (polar molecules)a. Dipole-dipole (polar molecules)b. London dispersion forces b. London dispersion forces

(nonpolar (nonpolar moleculesmolecules

Page 30: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Two of the intermolecular forces are Two of the intermolecular forces are associated with associated with POLARPOLAR structures. structures.

•Hydrogen BondingHydrogen Bonding •Dipole-dipole ForcesDipole-dipole Forces

One of the intermolecular forces is One of the intermolecular forces is associated with associated with NONPOLARNONPOLAR structures. structures.

•London Dispersion ForcesLondon Dispersion Forces

Page 31: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Hydrogen Bonding :Hydrogen Bonding :These occur between polar covalent molecules that possess a hydrogen bonded to an extremely electronegative element, specifically - N, O, and F.

Page 32: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

OOHH

HH

OOHH

HH

Hydrogen’s single electron is pulled Hydrogen’s single electron is pulled toward the very electronegative toward the very electronegative oxygen resulting in:oxygen resulting in:

1.1. Large partial chargesLarge partial charges

2.2. The unshielded nucleus of hydrogen The unshielded nucleus of hydrogen attraction to the unshared electron attraction to the unshared electron pairspairs

Covalent bondCovalent bond

Hydrogen bondHydrogen bond

Hydrogen Bonding :Hydrogen Bonding :

Page 33: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Hydrogen Bonding :Hydrogen Bonding :

Page 34: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Properities due to Hydrogen Bonding

• Higher than expected melting/boiling points

• More viscous substances (liquids are “thicker” to pour)

• Surface tension – an inward pull that minimizes the surface area of a liquid.

• Capillary Action

Page 35: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Hydrogen Bonding :Hydrogen Bonding :

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Hydrogen Bonding : Surface TensionHydrogen Bonding : Surface Tension

Page 37: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Only polar covalent molecules have the ability to form dipole-dipole attractions between molecules. Polar covalent molecules act as little magnets, they have positive ends and negative ends which attract each other.

Dipole-Dipole :Dipole-Dipole :

Page 38: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

Dipole-Dipole :Dipole-Dipole :

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• Because of the constant motion of the electrons, an atom or molecule can develop a temporary (instantaneous) dipole when its electrons are distributed asymmetrically about the nucleus.

• The attractive forces are responsible for Bromine being a liquid and Iodine a solid at room temperature.

London Dispersion Force :London Dispersion Force :

Page 40: Molecular Nomenclature and Geometry Chemistry Text Ch 6.1,6.2,6.5,16.1-16.3.

• The electron asymmetry about the nucleus induces a temporary attraction between the non-polar molecules causing the London Dispersion Force.

London Dispersion Force :London Dispersion Force :