Covalent BondsAtoms can form molecules by sharing electrons in the covalent bond. This is done only among non-

metal atoms.

Molecules

• Some elements in nature are found in the form of molecules

• Diatomic = 2 atoms BrINClHOF

• Compound composedOf molecules is called a Molecular compound

PROPERTIES

• Relatively low melting points and boiling points

• Many are gases and liquids at room temperature

• Composed of atoms of 2 or more nonmetals

Molecular Formulas

• Show how many atoms of each element a molecule contains

• Ex. H2O has 2 hydrogen atoms and 1 oxygen atom

• Doesn’t show shape of molecule or which atoms are covalently bonded and how

Dot Structures-Octet Rule(All atoms want 8 electrons around them.)

Valence electrons are those in the outermost orbitals. They are the ones that can form bonds.

Electron sharing occurs in such a way so that atoms attain the electron configuration of the noble gases.

SINGLE COVALENT BONDS

• Two atoms held together by sharing a pair of electrons. Can be shown by lewis dot or a dash

H H

UNSHARED PAIRS

In F2 each flourine contributes one electronThe electrons that are not shared are called Unshared pairs, lone pairs or nonbonding pairs

Draw Lewis structures

• NH3

• PCl3

• Cl2

• SBr2

DOUBLE AND TRIPLE COVALENT BONDS

Occurs when three pairs of electronsAre shared

Occurs when two pairs of electrons are shared

NASL Method for Lewis Dot Structures

• Helps to determine how to place electrons around an atom ( double/triple bonds + lone pairs)

• Exceptions to octet = H = 2, Be = 4, B= 6

STEPS1. Write a skeleton molecule with the lone atom in the

middle (Hydrogen can never be in the middle)2. Calculate (N) Needed which is the sum of electrons

needed for all atoms to obey the octet rule.

NASL MethodShow structure for CO2

1. O C O skeleton 2. Needed electrons C = 1 x 8 = 8

O = 2 x 8 = 16

N = 24

NASL METHOD

• Step 3; Calculate A (Available) = sum of all valence electrons. For anions and cations you need to subtract or add electrons here.

• Step 4; Calculate S ( Shared) = Difference between N and A

1 x 4 = 4 for Carbon

2 x 6 = 12 for Oxygen

CO2

16 A (available)

SharedNeeded – Available = 24-16= 8

NASL Method

• Divide S by 2 to obtain the number of bonds to be extended from the central atoms.

8 / 2 = 4 O::C::O

• Calculate L ( Lone-pair electrons ) the difference between A and S

16 – 8 = 8 .. .. O::C::O

●● ●●

Let's Try it!1.S

2.N

3.A

4.S

5.L

6.E ..H:O:H ●●

H O H Water H2O

2 x 2 = 4 for Hydrogen1 x 8 = 8 for Oxygen4+8=12 needed electrons

8 – 4 = 4 non-bonding electrons

2 x 1 = 2 for Hydrogen1 x 6 = 6 for Oxygen You have 8 available electrons

12 – 8 = 4/2 = Bonding

8 H12 N

4 B

4 NB

-

-

H:O:H ..H:O:H ●●

Let's Try it!1.S

2.N

3.A

4.S

5.L

6.E ..H:N:H ●●

HH N H Ammonia NH3

3 x 2 = 6 for Hydrogen1 x 8 = 8 for Nitrogen6+8=14 needed electrons

8-6 = 2 lone electrons

3 x 1 = 3 for Hydrogen1 x 5 = 5 for Nitrogen You have 8 available electrons

14 – 8 = 6/2 = 3 bonding pairs

8 H14 N

6 B

2 NB

-

-

..H:N:H

..H:N:H ●●

H

HH

REVIEW

• Draw lewis dot structures for the following

– PCL3

– CH4

Review Quiz #2

• Using NASL Show covalent bonding for the following compounds. Show all work for credit. ( 6 points )

SO2

NomenclatureNaming of Binary Molecular Compounds

Binary Compounds: Composed of two different elements that are nonmetals.

Ex. CO and CO2 (not carbon Oxide)

CO = Carbon monoxide = poisonous gasCO2 = carbon dioxide waste product of breathing

Need to differentiate different types of compounds by using prefixes. Tells you how many of each element are present

Mono = 1 Penta = 5Di = 2 Hexa = 6Tri = 3 Hepta = 7Tetra = 4 Octa = 8

Naming Guidelines

• 1. make sure you have a binary molecular compound composed of two nonmetals

• 2. Name must identify the elements and how many are present

• 3. Name the elements in the order listed• 4. Omit the prefix – mono when the first element only

has one– Ex. SF6 is sulfur hexaflouride NOT monosulfur hexaflouride

• 5. The suffix for the second element is -ide

Writing Formulas

• Use the prefixes in the name to determine the correct subscripts for the formula.

• Ex. Silicon Carbide ( no prefixes so must contain one of each) SiC

• Dinitrogen Tetroxide = N2O4

Let’s Practice!

• Phosphorus Pentachloride• Iodine Heptaflouride• Chlorine triflouride

OF2

SO2

N2O4

Using a few sentences discuss what the cartoon might mean in terms of how Cl and H bond

POLARITY

• Covalent bonds involve atoms sharing electrons (pulled in a tug of war)

• When electrons are pulled equally = nonpolar Covalent bond

• When electrons are pulled unequally = polar covalent bond

Electronegativity

• The magnitude of attraction for electrons is called “Electronegativity”. The more electronegative an atom is, the more it wants the electrons.

The higher the electronegativity Value the greater the ability to attract electrons

Bond types

WATER IS A POLAR MOLECULE

O = 3.5 ELECTRONEGATIVEH = 2.1 ELECTRONEGATIVE

DIFFERENCE = 1.4 = POLAR COVALENT

OXYGEN PULLS HYDROGENS ELECTRONS CLOSER THAN HYDROGEN CAN PULL OXYGENSELECTRONS. OXYGEN GETS AN OVERALL PARTIAL NEGATIVE CHARGE AND HYDROGENGETS AN OVERALL PARTIAL POSTITIVE CHARGE DESIGNATED BY A GREEK DELTA SIGN

VSEPR Theory

• Electron dot structures fail to reflect the 3-dimensional shape of molecules

Molecules in reality are 3 dimensional and can be explained by the VSEPR theory

VSEPR Theory

• Explains 3-D shape of molecules• Based on the theory that repulsion occurs

between electron pairs and causes a variety of molecular shapes.

• Electrons want to stay as far apart as possible• Can be determined by first looking at the lewis

dot structure• Counting how many electron clouds (pairs) are

radiating

LINEAR MOLECULES

The simplest structure has two groups around the central atom. Carbon monoxide, CO2, is an example of this kind of shape. The two groups of electrons in the two double bonds repel each other and assume a shape with an angle of 180 degrees.

MOLECULAR SHAPES

Review

Trigonal planar = 3 bondingNo lone pairs

Pyramidal = 3 bonding pairsAnd a lone pair