COVALENT BONDING

Chapter 6

CHAPTER 6 BEGINNING ASSIGNMENTS Vocabulary page 226 Section 6.1 Reading, 10 questions and

their answers, pages 194-201

COVALENT BOND Covalent Bond – a bond that occurs

when 2 atoms share valence electrons. Covalent bonds usually occur between

nonmetal atoms. How they form:1. As 2 atoms approach each other, the

attractions are initially stronger than the repulsions.

2. The covalent bond forms when the energy is minimized; or when attractions = repulsions.

COVALENT BOND

IONIC VS. COVALENT BONDING video

COVALENT BOND Bond Length – average distance

between 2 atoms covalently bonded. Bond Energy – energy needed to break a

covalent bond. High bond energy = short bond length

TYPES OF COVALENT BONDS1. Nonpolar Covalent Bond – bond in

which electrons are shared equally.2. Polar Covalent Bond – bond in which

electrons are shared unevenly because they are pulled toward the more electronegative atom.

This creates a dipole – the bond has a partially positive and negative end.

Electronegativity – ability of an atom to attract electrons to itself.

Polar Covalent Bonding

PREDICTING BOND TYPE If the electronegativity difference

between atoms is: from 0 – 0.4 NONPOLAR

from 0.5 – 2.0 POLAR

Greater than 2.0 IONIC

ALSO ON PAGE 198

LEWIS DOT SYMBOLS Lewis Dot Symbol (Electron Dot Symbol)

– uses dots to depict the number of valence electrons an atom has.

Valence Electrons – electrons in the highest occupied energy level of an atom that participate in chemical bonding.

VALENCE ELECTRONS

DRAW LEWIS DOT SYMBOLS FOR THE FOLLOWING ATOMS calcium

iodine

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p2

neon

aluminum

MOLECULAR COMPOUNDS Molecular Compound – compound in

which atoms, not ions, are covalently bonded by sharing electrons to form molecules.

Ionic Compounds are named with the Stock system

Molecular Compounds are named with the prefix system.

Ionic compounds typically contain metals and nonmetals.

Molecular compounds typically contain only nonmetals.

NAMING BINARY MOLECULAR COMPOUNDS – PREFIX SYSTEM

1. Use the full name of the 1st element. Only add a prefix if there is more than 1 atom.

1 = mono- 2 = di- 3 = tri- 4 = tetra-

5 = penta- 6 = hexa- 7 = hepta- 8 = octa- 9 = nona- 10 = deca-2. Change the name of the 2nd element to

end in –ide. Always add a prefix to indicate the number of atoms.

3. Drop the ‘o’ or ‘a’ from a prefix if an element name begins with a vowel.

WRITE FORMULAS carbon dioxide

dinitrogen pentoxide

sulfur hexafluoride

dihydrogen monoxide

WRITE NAMES CCl4

N2O3

PF5

Cl2O

NAME USING THE RIGHT SYSTEM AlBr3

AsBr3

Cu2S

P2O3

LEWIS STRUCTURES Lewis Structure – diagram that shows

the structure of a covalently bonded molecule using only valence electrons. It includes lone pairs and bond pairs of atoms bonded together.

Lone Pair – unshared pair of electrons not involved in a covalent bond.

Bond Pair – pair of electrons shared by 2 atoms to form a covalent bond.

Lone pairs are represented with dots; bond pairs with dashes (-).

LEWIS STRUCTURES Single Bond – bond in which one pair of

electrons is shared between atoms. Double Bond – bond in which 2 pairs of

electrons are shared. Triple Bond – bond in which 3 pairs of

electrons are shared. Triple bonds tend to have the highest

bond energy and shortest bond length.

HOW TO DRAW LEWIS STRUCTURES1. Determine the total number of valence

electrons from all atoms in the molecule.

2. Choose a central atom and arrange all atoms to show how they are bonded.

C is ALWAYS a central atom. Otherwise, the first atom in the formula is probably the central atom.

3. Fill in lone pairs until all atoms have an octet. H should have just 2 valence electrons (exception to octet rule!).

HOW TO DRAW LEWIS STRUCTURES4. Check to make sure the total number

of electrons is correct. If not, change the bond types.

PRACTICE TIME1. CCl2F2

2. HOCl

3. CS2

4. SO2

5. NF3

LEWIS STRUCTURES OF POLYATOMIC IONS Anions – ADD electrons to the total due

to the negative charge.

Cations – must SUBTRACT electrons from the total due to the positive charge.

RESONANCE STRUCTURES Resonance Structures – equivalent Lewis

structures that can be drawn to represent the same molecule or ion.

EXCEPTIONS TO THE OCTET RULE1. Less than an Octet Hydrogen will have 2 valence electrons Boron is stable having 6 valence electrons2. Odd Number of Valence Electrons Causes the molecule or ion to be very

unstable and reactive The more electronegative atom(s) will

have octets.3. Expanded Octet – elements in the 3rd

period of the PT and below can be stable having more than 8 valence electrons as central atoms.

SECTION 6.2 QUIZ Names / formulas of molecular

compounds (prefix system) Lewis Dot Symbols and valence

electrons Drawing Lewis Structures

WHAT TYPE OF BOND? Si - O

Cl – Cl

K – S

Li - F

WRITE THE FORMULA OR NAME SeBr6

S2Cl3

P2O5

dinitrogen monoxide

phosphorus trihydride

TODAY: Finish Molecular Modeling Lab in groups. Read section 6.2 and write 10 questions

and answers.

MOLECULAR GEOMETRY VSEPR Theory – Valence Shell Electron

Pair Repulsion theory Electron pairs will orient themselves as

far apart as possible to minimize repulsions.

Shapes of molecules are based on how many ATOMS and LONE PAIRS are around the central atom.

LINEAR

BENT

TRIGONAL PLANAR

TRIGONAL PYRAMIDAL

TETRAHEDRAL

TRIGONAL BIPYRAMIDAL

OCTAHEDRAL

MOLECULAR POLARITY A molecule / polyatomic ion is POLAR if:1. At least one bond is POLAR

(electronegativity difference of 0.5 or more.

2. All dipole moment arrows point in the same general direction (left, right, up, down).

Dipole moment – arrow drawn to show the more electronegative atom in a polar bond.

Polarity of Water

MOLECULAR POLARITY

ASSIGNMENT - #32 PAGE 2291. Draw Lewis Structures showing the

correct shape.2. Add dipole moment arrows (if there are

any).3. Is the molecule Polar or Nonpolar?

TODAY’S ASSIGNMENTS1. Read section 6.4 and write 10

questions and answers. Turn in.2. Complete Term Review #1-10 page

227 and Test Prep #1-12 page 231.3. If finished, you should begin the

chapter 6 review sheet.