1. Chapter 1
Section 4
Covalent Bonding

2. Sharing is Caring
The atoms held together by sharing electrons are joined by a Covalent Bond.

3. 2. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons.
Oxygen Atom
Oxygen Atom
Oxygen Molecule (O2)

4. Molecules and Molecular Compounds
Molecule is a neutral group of atoms joined together by covalent bonds.
Diatomic molecule is a molecule consisting of two atoms.
A compound composed of molecules is called a molecular compound.

5. Properties
Molecular compounds tend to have relatively lower melting and boiling points than ionic compounds.
Many are gases or liquids at room temperature.
Most are formed from atoms of two or more nonmetals.

6. Molecular Formulas
A molecular formula is the chemical formula of a molecular compound.
It shows how many atoms of each element a molecule contains.
CO2 Carbon Dioxide
1 Carbon Atom
2 Oxygen Atoms

7. Ionic Vs. Covalent Bond

8. Covalent Bonds

9. Chapter 2 Chemical Principles
Bonding
Covalent bonding

10. So
what
are
covalent
bonds?

11. In covalent bonding,
atoms still want to achieve
a noble gas configuration
(the octet rule).

12. But rather than losing or gaining electrons,
In covalent bonding,
atoms still want to achieve
a noble gas configuration
(the octet rule).
But rather than losing or gaining
electrons,
atoms now share an electron pair.

13. The shared electron pair is called a bonding pair
In covalent bonding,
atoms still want to achieve
a noble gas configuration
(the octet rule).
But rather than losing or gaining
electrons,
atoms now share an electron pair.
The shared electron pair
is called a bonding pair

14. Chlorine
forms a
covalent
bond
with
itself
Cl2

15. How
will
two
chlorine
atoms
react? Cl Cl

16. Cl Cl Each chlorine atom wants to
gain one electron to achieve an octet

17. Cl Cl do to achieve an octet? What’s the solution – what can they
Neither atom will give up an electron –
chlorine is highly electronegative.
What’s the solution – what can they
do to achieve an octet?

18. Cl Cl do to achieve an octet? What’s the solution – what can they
Neither atom will give up an electron –
chlorine is highly electronegative.
What’s the solution – what can they
do to achieve an octet?

19. Cl Cl
octet

20. Cl Cl octet circle the electrons for each atom that completes
their octets

21. Cl Cl The octet is achieved by each atom sharing the
electron pair in the middle
circle the electrons for
each atom that completes
their octets

22. Cl Cl The octet is achieved by each atom sharing the
electron pair in the middle
circle the electrons for
each atom that completes
their octets

23. Cl Cl This is the bonding pair circle the electrons for
each atom that completes
their octets

24. Cl Cl It is a single bonding pair circle the electrons for
each atom that completes
their octets

25. Cl Cl It is called a SINGLE BOND circle the electrons for
each atom that completes
their octets

26. Single bonds are abbreviatedCl Cl
Single bonds are abbreviated
with a dash
circle the electrons for
each atom that completes
their octets

27. This is the chlorine molecule,Cl Cl
This is the chlorine molecule,
Cl2
circle the electrons for
each atom that completes
their octets

28. O2
Oxygen is also one of the diatomic molecules

29. O
How will two oxygen atoms bond?

30. O
Each atom has two unpaired electrons

31. O

32. O

33. O Oxygen atoms are highly electronegative.
So both atoms want to gain two electrons.

34. Both electron pairs are shared.

35. O O
6 valence electrons
plus 2 shared electrons
= full octet

36. O O
6 valence electrons
plus 2 shared electrons
= full octet

37. O O
two bonding pairs,
making a double bond

38. O O =
For convenience, the double bond
can be shown as two dashes.

39. This is the oxygen molecule,=
this is so cool!!
This is the oxygen molecule, O2

40. Multiple Covalent bonds
Only 7 electrons does
Not meet Octet Rule!
Need to share
Another pair of
electrons O O
Sharing One Pair of electrons
One Covalent Bond O O O O
A Double Bond can be represented by a double line
Sharing Two Pairs of electrons
Two Covalent Bonds
A Double Bond

41. Multiple Covalent bonds
Nitrogen N N
Sharing Three Pairs of electrons
Three Covalent Bonds
A Triple Bond N N
A Triple Bond can be represented by a Triple line

42. Coordinate Covalent Bond
both electrons contributed by one atom of pair
NH3 + H > NH4+
H2O + H > H3O+

43. Coordinate Covalent Bond
ammonium ion

44. Drawing Lewis Dot Structures
Predict the location of the atoms
Hydrogen is a terminal atom
The central atom has the smallest electronegativity.
Count the valence electrons.
Draw a single covalent bond between the central atom and the surrounding atoms.
Subtract the number of electrons in the single covalent bonds from the total number of electrons in 2.
Use the remaining electrons to complete the octets of each atom.
If the central atom does not have a complete octet then try double or triple bonds.

45. Drawing Lewis Dot Structures
Draw Lewis Dot Structures for:
PH3
H2S
HCl
CCl4
SiH4
CH2Cl2

46. Bond Dissociation Energies
The energy required to break the bond between two covalently bonded atoms.

47. Relate the strength of covalent bonds to bond length
The more bonds located between 2 atoms, the shorter the bonds are
The shorter a bond is, the stronger it is
H – H single bond, not too strong
O=O double bonds, stronger
NΞN triple bonds, strongest

48. Endothermic/Exothermic
In chemical reactions, bonds are broken, then new bonds are formed
Endothermic
More energy is required to break the old bonds than is released by the formation of new bonds
Energy is taken in (colder)
Exothermic
More energy is released when forming new bonds than is used to break the old bonds
Energy is given off (hotter)

49. Exceptions to Octet Rule
NO2 nitrogen dioxide
resonance

50. Exceptions to Octet Rule
PF5
expanded octet

51. Exceptions to Octet Rule
SF6
Expanded octet

52. INTRODUCTION
A) Lewis structures do not indicate the three dimensional shape of a molecule. They do not show the arrangement space of the atoms, what we call the molecular geometry or molecular structure.
B) Molecules have definite shapes and the shape of a molecule controls some of its chemical and physical properties.

53. II. Valence Shell Electron Pair Repulsion Theory - VSEPR - predicts the shapes of a number of molecules and polyatomic ions.
A) Assumptions of VSEPR Theory
1) Electron pairs in the valence shell of an atom tend to orient themselves so that the total energy is minimized. This means that: the electrons will approach the nucleus as close as possible yet take positions as far away from each other as possible to minimize _______________ .

54. 2) Because lone pairs of electrons are spread out more broadly than bond pairs, repulsions are greatest between two lone pairs, intermediate between a lone pair and a bond pair, and weakest between two bonding pairs of electrons.
3) Repulsive forces decrease rapidly with increasing interpair angle - greatest at 90o, much weaker at 120o, and very weak at 180o.
B) What are the ideal arrangements of electron pairs to minimize repulsions?

55. Note that each atom has a single, unpaired electron.
Bond Formation
A bond can result from an overlap of atomic orbitals on neighboring atoms. Cl H •• • +
Overlap of H (1s) and Cl (2p)
Note that each atom has a single, unpaired electron.

56. Double and even triple bonds are commonly observed for C, N, P, O, and S
H2CO
SO3
C2F4

57. Some Common Geometries
Linear
Tetrahedral
Trigonal Planar

60. Structure Determination by VSEPR
Water, H2O
The electron pair geometry is TETRAHEDRAL
2 bond pairs
2 lone pairs
The molecular geometry is BENT.

61. Structure Determination by VSEPR
Ammonia, NH3
The electron pair geometry is tetrahedral.
The MOLECULAR GEOMETRY — the positions of the atoms — is TRIGONAL PYRAMID.

62. Bond Polarity Cl has a greater share in bonding electrons than does H.
HCl is POLAR because it has a positive end and a negative end. (difference in electronegativity)
Cl has a greater share in bonding electrons than does H.
Cl has slight negative charge (-d) and H has slight positive charge (+ d)

63. Bond Polarity
This is why oil and water will not mix! Oil is nonpolar, and water is polar.
The two will repel each other, and so you can not dissolve one in the other

64. Bond Polarity Polar dissolves Polar Nonpolar dissolves Nonpolar
“Like Dissolves Like”
Polar dissolves Polar
Nonpolar dissolves Nonpolar

65. Electronegativity Difference
If the difference in electronegativities is between:
1.7 to 4.0: Ionic
0.3 to 1.7: Polar Covalent
0.0 to 0.3: Non-Polar Covalent
Example: NaCl
Na = 0.8, Cl = 3.0
Difference is 2.2, so
this is an ionic bond!

66. Remember: BrINClHOF Diatomic Elements
These elements do not exist as a single atom; they always appear as pairs
When atoms turn into ions, this NO LONGER HAPPENS!
Hydrogen
Nitrogen
Oxygen
Fluorine
Chlorine
Bromine
Iodine
Remember: BrINClHOF

67. Polar Covalent Bonds: Unevenly matched, but willing to share.

68. Van der Waals Forces
Small, weak interactions between molecules

69. Van der Waals Forces Intermolecular: between molecules (not a bond)
Intramolecular: bonds within molecules (stronger)

70. 3 Types of Van der Waals Forces
1)    dipole-dipole
2)    dipole-induced dipole
3) dispersion

71. Dipole-Dipole
Two polar molecules align so that d+ and d- are matched (electrostatic attraction)
Ex: ethane (C2H6) vs. fluromethane (CH3F)
Occurs when polar molecules are attracted to one another.
The slightly region of a polar molecule is weakly attracted to the slightly positive region of another polar molecule.
Similar to but much weaker than ionic bonds.

72. Dispersion Forces
The weakest of all molecular interactions, are caused by the motion of electrons.
Dispersion is the ONLY intermolecular attraction that occurs between non-polar molecules

73. Review Dipole – between two polar molecules Dispersion-
between two non-polar molecules

74. Hydrogen Bonding STRONGEST Intermolecular Force!!
A special type of dipole-dipole attraction
Bonds form due to the polarity of water.
Ice
Liquid

75. Hydrogen Bonding con’t
Hydrogen bonds keep water in the liquid phase over a wider range of temperatures than is found for any other molecule of its size

76. How many drops can you get on a penny?
Water?
Why is there a difference???
Water has strong Hydrogen Bonds and TTE has weaker intermolecular forces

77. How is surface tension affected by soap?
Breaks the surface tension!

78. Intermolecular Attractions and Molecular Properties
The physical properties of a compound depend on the type of bonding it displays-in particular, on whether it is ionic or covalent.
Network Solids are solids in which all of the atoms are covalently bonded together.
Melting a network solid would require breaking covalent bonds throughout the solid.
Diamond does not melt; rather it vaporizes to a gas at 3500 degrees Celsius and above.

79. Review of Chemical Bonds
There are 3 forms of bonding:
_________—complete transfer of 1 or more electrons from one atom to another (one loses, the other gains) forming oppositely charged ions that attract one another
_________—some valence electrons shared between atoms
_________ – holds atoms of a metal together
Most bonds are somewhere in between ionic and covalent.

80. Review of Valence Electrons
Number of valence electrons of a main (A) group atom = Group number

81. Review of Valence Electrons
Remember from the electron chapter that valence electrons are the electrons in the OUTERMOST energy level… that’s why we did all those electron configurations!
B is 1s2 2s2 2p1; so the outer energy level is 2, and there are 2+1 = 3 electrons in level 2. These are the valence electrons!
Br is [Ar] 4s2 3d10 4p5 How many valence electrons are present?

82. Bond and Lone Pairs
Valence electrons are distributed as shared or BOND PAIRS and unshared or LONE PAIRS. • •• H Cl
shared or
bond pair
lone pair (LP)
This is called a LEWIS structure.