Chapter 8

1
Chapter 8 Covalent Bonding
The unspoken hero Covalent Bond ?

• Mr. Samaniego
• Lawndale High School

2
Review of Chapter 7

• In Chapter 7, we learned about electrons being
  transferred (given up or stolen away)

• This type of tug of war between a METAL and
  NONMETAL is called an IONIC BOND, which results
  in a SALT being formed

3
Chapter 8.1 Molecular Compounds

• In this chapter, you will learn about another
  type of bond in which electrons are shared

• Covalent Bonds are atoms held together by
  SHARING electrons between NONMETALS

4
Salt versus Molecules

• A metal cation and nonmetal anion are joined
  together by an ionic bond called SALT

• A group of atoms joined together by a covalent
  bond is called a MOLECULE

• A Compound is a group of two or more elements
  bonded together (Ionic or Covalent).

5
Monatomic vs. Diatomic Molecules

• Most molecules can be monatomic or diatomic

• Diatomic Molecule is a molecule consisting of two
  atoms

• There are 7 diatomic molecules (SUPER 7) N2,
  O2, F2, Cl2, Br2, I2, H2

• You can also remember them as H2O2F2Br2I2N2Cl2

6
Properties of Molecular Compounds

• Liquids or gases at room temperature

• Lower Melting Points than Ionic Compounds (which
  means that they are weaker than ionic)

7
Molecular Formulas

• The Molecular Formula is the formula of a
  molecular compound

• It shows how many atoms of each element a
  molecule contains

• Example
• H2O contains 3 atoms (2 atoms of H, 1 atom of O)
• C2H6 contains 8 atoms (2 atoms of C, 6 atoms of H)

8
Practice

• How many atoms total and of each do the following
  molecular compounds contain?
• H2
• CO
• CO2
• NH3
• C2H6O

9
Practice True or False

1. All molecular compounds are composed of atoms of
   two or more elements.
2. All compounds are molecules.
3. Molecular compounds are composed of two or more
   nonmetals.
4. Atoms in molecular compounds exchange electrons.
5. Molecular compounds have higher melting and
   boiling points than ionic compounds.

TRUE
FALSE
TRUE
FALSE
FALSE
10
(No Transcript)
11
Ionic versus Covalent
IONIC COVALENT
Bonded Name Salt Molecule
Bonding Type Transfer e- Share e-
Types of Elements Metal Nonmetal Nonmetals
Physical State Solid Solid, Liquid, or Gas
Melting Point High (above 300ºC) Low (below 300 ºC)
Solubility Dissolves in Water Varies
Conductivity Good Poor
12
Chapter 8.2 Covalent Bonding

• Remember that ionic compounds transfer electrons
  in order to attain a noble gas electron
  configuration

• Covalent compounds form by sharing electrons to
  attain a noble gas electron configuration

• Regardless of the type of bond, the Octet Rule
  still must be obeyed (8 valence electrons)

13
Single Covalent Bond

• A Single Covalent Bond consists of two atoms held
  together by sharing 1 pair of electrons (2 e-)

14
Electron Dot Structure
15
Shared versus Unshared Electrons

• A Shared Pair is a pair of valence electrons that
  is shared between atoms

• An Unshared Pair is a pair of valence electrons
  that is not shared between atoms

16
Practice Lewis Dot Structures
Chemical Formula of Valence Electrons Single Line Bond Structure of Remaining Electrons Lewis Dot Structure Octet Check All Atoms8 Hydrogen2
F2
H2O
NH3
CH4
17
Double Covalent Bonds

• Sometimes atoms attain noble gas configuration by
  sharing 2 or 3 pairs of electrons

• A Double Covalent Bond is a bond that involves 2
  shared pairs of electrons (4 e-)

18
Triple Covalent Bond

• A Triple Covalent Bond is a bond that involves 3
  shared pairs of electrons (6 e-)

19
Covalent Bonds
20
Practice Lewis Dot Structure
Chemical Formula of Valence Electrons Single Line Bond Structure of Remaining Electrons Lewis Dot Structure Octet Check All Atoms8 Hydrogen2
O2
CO2
N2
HCN
21
Bond Dissociation Energy

• Bond Dissociation Energy is the energy required
  to break a bond between two atoms

• A large bond dissociation energy corresponds to a
  strong bond which makes it unreactive

• Carbon has strong bonds, which makes carbon
  compounds stable and unreactive

22
Chapter 8.3 - Bonding Theories

• So far, the orbitals we have been discussing are
  atomic orbitals (s, p, d, f) for each atom

• When two atoms combine, their atomic orbitals
  overlap and they make molecular orbitals

• A Molecular Orbital is an orbital that applies to
  the entire molecule, instead of just one atom

23
Molecular Orbitals

• Just as atomic orbitals belong to a particular
  atom, a molecular orbital belongs to molecules
  as a whole

• Each orbital is filled with 2 electrons

• A Bonding Orbital is an orbital that can be
  occupied by two electrons of a covalent bond
  (its the space in between the two atoms)

• There are 2 types of bonding orbitals sigma
  and pi

24
Sigma Bond (?)

• A Sigma Bond is when 2 atomic orbitals combine to
  form a molecular orbital that is symmetrical
  around the axis

S orbitals overlapping
P orbitals overlapping end-to-end
25
Pi Bond (?)

• Pi bonding electrons are likely to be found in a
  sausage-shape above and below the axis

• Pi bonds are weaker than sigma bonds because they
  overlap less

P orbitals overlapping side-by-side
26
VSEPR Theory

• VSEPR Theory predicts the 3D shape of molecules

• According to VSEPR, the repulsion of electrons
  causes the shape of the molecule to adjust so
  that the electrons are far apart

27
A Few VSEPR Shapes
28
Nine possible molecular shapes
29
VSEPR Theory

• Unshared pairs of electrons are very important in
  predicting the shapes of molecules

• Unshared pairs of electrons are very important in
  predicting the shapes of molecules

• Each bond (single, double, or triple) or unshared
  pair is considered a steric number

• Use the steric number to predict the molecular
  geometry

• VSEPR can only be used with the central atom

30
Practice

• Methane (CH4) tetrahedral
• Ammonia (NH3) pyramidal
• Water (H2O) bent
• Carbon Dioxide (CO2) - linear

31
Hybrid Orbitals

• VSEPR is good at describing the molecular shapes,
  but not the types of bonds formed

• Orbital hybridization provides information about
  both molecular bonding and molecular shape

• In hybridization, several atomic orbitals mix to
  form hybrid orbitals

32
Bond Hybridization

• Hybridization Involving Single Bonds sp3
  orbital
• Ethane (C2H6)

• Hybridization Involving Double Bonds sp2
  orbital
• Ethene (C2H4)

• Hybridization Involving Triple Bonds sp orbital
• Ethyne (C2H2)

33
Chapter 8.4 Polar Bonds and Molecules

• There are two types of covalent bonds
• Nonpolar Covalent Bonds (share equally)
• Polar Covalent Bonds (share unequally)

34
Polar Covalent

• A Polar Covalent Bond is unequal sharing of
  electrons between two atoms (HCl)

• In a polar covalent bond, one atom typically has
  a negative charge, and the other atom has a
  positive charge

35
Nonpolar Covalent Bond

• A Nonpolar Covalent Bond is equal sharing of
  electrons between two atoms (Cl2, N2, O2)

36
(No Transcript)
37
Classification of Bonds

• You can determine the type of bond between two
  atoms by calculating the difference in
  electronegativity values between the elements

Type of Bond Electronegativity Difference
Nonpolar Covalent 0 ? 0.4
Polar Covalent 0.5 ? 1.9
Ionic 2.0 ? 4.0
38
Practice

• What type of bond is HCl? (H 2.1, Cl 3.1)

Difference 3.1 2.1 1.0
Therefore it is polar covalent bond.
Your Turn To Practice

• N(3.0) and H(2.1)
• H(2.1) and H(2.1)
• Ca(1.0) and Cl(3.0)

• Al(1.5) and Cl(3.0)
• Mg(1.2) and O(3.5)
• H(2.1) and F(4.0)

39
Dipole

• No bond is purely ionic or covalent they have a
  little bit of both characters

• When there is unequal sharing of electrons a
  dipole exists

• Dipole is a molecule that has two poles or
  regions with opposite charges

• A dipole is represented by a dipole arrow
  pointing towards the more negative end

40
Practice Drawing Dipoles

• P- Br
• P 2.1
• Br 2.8

P Br ? ?-

• Practice
• H(2.1) S(2.5)
• F(4.0) - C(2.5)
• C(2.5) - Si(1.8)
• N(3.0) O(3.5)

41
Attractions Between Molecules

• Besides ionic, metallic, and covalent bonds,
  there are also attractions between molecules

• Intermolecular attractions are weaker than ionic,
  covalent, and metallic bonds

• There are 2 main types of attractions between
  molecules Van der Waals and Hydrogen

42
Van der Waals Forces

• Van der Waals forces consists of the two weak
  attractions between molecules

1. dipole interactions polar molecules
attracted to one another
2. dispersion forces caused by the motion of
electrons (weakest of all forces)
43
Hydrogen Bond

• Hydrogen Bonds are forces where a hydrogen atom
  is weakly attracted to an unshared electron pair
  of another atom

44
Hydrogen Bond

• This other atom may be in the same molecule or in
  a nearby molecule, but always has to include
  hydrogen

• Hydrogen Bonds have about 5 of the strength of
  an average covalent bond
• Hydrogen Bond is the strongest of all
  intermolecular forces

45
Intermolecular Attractions

• A few solids that consist of molecules do not
  melt until the temperature reaches 1000ºC or
  higher called network solids (Example diamond,
  silicon carbide)

• A Network Solid contains atoms that are all
  covalently bonded to each other

• Melting a network solid would require breaking
  bonds throughout the solid (which is difficult to
  do)

46
Classwork

• Chapter 8 Assessment Page 247
• s 39-41, 43-46, 51, 53, 54, 57-59, 61, 65, 68,
  83, 85, 86, 89, 96, 99, 100