1. Cosmic voyage (Morgan Freeman) 40 min
BONDING
Cosmic voyage (Morgan Freeman) 40 min

2. Valence Electrons are Involved in Bonding
The electrons responsible for the chemical properties of atoms
Electrons in the outer energy level or highest occupied energy level
Kernel (Core) electrons
those in the energy levels below.

3. Chemical Bonding Chemical Bond
The attractive force between atoms or ions
Formed when 2 atoms share electrons or when electrons are transferred from one atom to another
The Octet Rule
In forming compounds, atoms tend to achieve a noble gas configuration - 8 in the outer level is stable
When chemical bonds are formed energy is released (exothermic)
When chemical bonds are broken energy is absorbed (endothermic)

4. Electron Dot Diagrams AKA Lewis Structures
A way of showing & keeping track of valence electrons
How to write them
Write the element’s symbol
It represents the nucleus and core electrons
Put one dot for each valence electron (8 maximum)
2 electrons pair at 12 o’clock position
The next 3 are dispersed around the symbol as follows: 1 at 3 o’clock, 1 at 6 o’clock, 1 at 9 o’clock, the last 3 are dispersed the same way X

5. N Electron Dot Diagram Nitrogen has 5 valence electrons
- First write the symbol. N
-The first 2 belong at the 12 o’clock position as a pair
The last 3 belong separate at the 3 o’clock, 6 o’clock, and 9 o’clock position
(maximum of 2 electrons per side in any diagram except for H or He)

6. Ionic Bonding

7. Formation of Cations
Metals lose electrons to attain a noble gas configuration.
Form positive ions (cations)
If we look at the electron configuration, it makes sense to lose electrons:
Na valence electron
Na This is a noble gas configuration (neon) with 8 electrons in the outer level.

8. Electron Dots For Cations
Metals will have few valence electrons (usually 3 or less); calcium has only 2 valence electrons Ca
Calcium Atom Electron Configuration:
2 Valence Electrons

9. Electron Dots For Cations
Metals will have few valence electrons
Metals will lose the valence electrons to achieve a noble gas configuration Ca

10. Electron Dots For Cations
Metals will have few valence electrons
Metals will lose the valence electrons to achieve a noble gas configuration
Forming positive ions
Ca2+
This is named the calcium ion.
NO DOTS are now shown for the cation.

11. Electron Configurations: Anions
Nonmetals gain electrons to attain noble gas configuration.
Form negative ions (anions)
S = = 6 valence electrons
S2-= = noble gas configuration.
Halide ions are ions from chlorine or other halogens that gain electrons

12. Electron Dots For Anions
Nonmetals will have many valence electrons (usually 5 or more)
They will gain electrons to fill outer shell. P
P3-
This is called the phosphide ion

13. Stable Electron Configurations
All atoms react to try and achieve a noble gas electron configuration.
8 valence electrons = already stable!
This is the octet rule (8 in the outer level is particularly stable). Ar

14. Ionic Bonding Ionic Bond
Force of attraction that holds oppositely charged ions together
The bond is formed through the transfer of electrons.
Electrons are transferred to achieve noble gas configuration.
Anions and cations are held together by opposite charges.
Resulting compound is an ionic compound

15. Ionic Compounds Ionic compounds Electrically neutral compound
Metal and non-metal
Salts are most common ionically bonded substances
Difference in electronegativity between atoms in compound must be 1.7 or greater (very large)
More electronegative atom takes electron

16. Ionic Bonding Na Cl
The metal (sodium) tends to lose its one electron from the outer level.
The nonmetal (chlorine) needs to gain one more to fill its outer level, and will accept the one electron that sodium is going to lose.

17. Result
Na+
Cl -
Remember that NO DOTS are now shown for the cation!

18. Ionic Bond

19. Ionic Bonding
Lets do an example by combining calcium and phosphorus: Ca P
All the electrons must be accounted for, and each atom will have a noble gas configuration (which is stable).

20. Ionic Bonding
Step 1 – Calcium atom donates its 2 valence electrons to phosphorus P Ca

21. Ionic Bonding
Ca2+ P
Results in 1 calcium ion and a phosphorus atom with 7 valence electrons

22. Ionic Bonding
Step 2 – Phosphorus still needs one more electron for the stable noble gas electron configuration. We can add another calcium atom
Ca2+ P Ca

23. Ionic Bonding
Ca2+
P 3- Ca
Results in 1 calcium ion, 1 phosphide ion and a calcium atom with 1 valence electron

24. Ca2+ P 3- Ca P Ionic Bonding
Step 3 – Calcium needs to donate its one valence electron for the stable noble gas electron configuration. We can add another phosphorus atom
Ca2+
P 3- Ca P

25. Ca2+ P 3- Ca2+ P Ionic Bonding
Results in 2 calcium ions, 1 phosphide ion and a phosphorus atom with 6 valence electrons

26. Ca2+ P 3- Ca2+ P Ca Ionic Bonding
Step 4 – the phosphorus atom still needs 2 electrons for the stable noble gas electron configuration. We can add another calcium atom
Ca2+
P 3-
Ca2+ P Ca

27. Ionic Bonding
Ca2+
P 3-
Ca2+ P Ca

28. Ca2+ P 3- Ca2+ P Ca2+ Ionic Bonding 3- = Ca3P2
Results in 3 calcium ions and 2 phosphide ions, all with a stable noble gas electron configuration of 8 valence electrons
= Ca3P2

29. Chemical formula refers to a ratio known as a formula unit
Formula unit – the lowest whole number ratio of ions in an ionic compound
Note – the formula NaCl does not represent a single discrete unit like a molecule (it’s not a molecule!)

30. Structure of Sodium Chloride

32. Properties of Ionic Compounds
Crystalline solids
a regular repeating arrangement of ions in the solid
Component ions in crystal are arranged in repeating 3-dimensional patterns
Fluorite - CaF2

33. Properties of Ionic Compounds
Ions are strongly bonded together.
Structure is rigid
High melting points
Very stable structure
Poor conductors in the solid state

34. Do Ionic Compounds Conduct Electricity ?
Conducting electricity means allowing charges to move.
In a solid, the ions (charged atoms) are locked in place
Do not conduct electricity
Ionic solids are insulators

35. Do Ionic Compounds Conduct Electricity?
When melted, the ions can move around.
Melted ionic compounds conduct electricity.
NaCl: must get to about 800ºC.
Dissolved in water, ionic compounds also conduct
Ions are free to move in aqueous solutions
When melted or dissolved regular crystal structure of ionic compound breaks and ions can move

36. The ions are free to move when they are molten (or in aqueous solution (dissolved)), and thus they are able to conduct the electric current.

37. Metallic Bonds Metals atoms lose valence electrons very easily
Metals are made of closely packed cations rather than neutral atoms
The force of attraction that holds metals together are called metallic bonds
Metallic bonds consist of the attraction of the free-floating valence electrons for the positively charged metal ions
Think of metal atoms as different metal ions (cations) floating in a sea of electrons

38. Metallic Bond

40. Sea of Electrons + Electrons are free to move through the solid.
This explains many physical properties of metals
Metals conduct electricity because the electrons can flow freely in them +

41. Metals are Malleable Hammered into shape (bend).
Also ductile - drawn into wires.
Both malleability and ductility explained in terms of the mobility of the valence electrons
A sea of drifting valence electrons insulates the metal cations from one another so the cations do not repel each other

42. Due to the mobility of the valence electrons, metals have:
Notice that the ionic crystal breaks due to ion repulsion!
1) Ductility
2) Malleability
and

43. Malleable +
Force

44. Malleable
Mobile electrons allow atoms to slide by, sort of like ball bearings in oil. +
Force

45. Ionic solids are brittle
On the other hand…
Ionic solids are brittle
Force + -

46. Ionic solids are brittle
Strong repulsion breaks a crystal apart, due to similar ions being next to each other. + -
Force + -

47. Alloys We use lots of metals every day, but few are pure metals
Alloys are mixtures of 2 or more elements, at least 1 is a metal
Made by melting a mixture of the ingredients, then cooling
Brass: an alloy of Cu and Zn
Bronze: Cu and Sn

48. Why use alloys? Properties are often superior to the pure element
Sterling silver (92.5% Ag, 7.5% Cu) is harder and more durable than pure Ag, but still soft enough to make jewelry and tableware
Steels are very important alloys
corrosion resistant, ductility, hardness, toughness, cost

49. Covalent Bond Attraction between neutral atoms
formed by sharing e- between two nonmetals

50. Covalent Bond
covalent bonds result in discrete molecules
NH3
Cl2
H2O

51. Covalent Bond Nonpolar Covalent Bond e- are shared equally
usually identical atoms

52. + - Covalent Bond Polar Covalent Bond
e- are shared unequally between 2 different atoms
results in partial opposite charges + -

53. Nonpolar Covalent
Polar Covalent
Ionic
View Bonding Animations.

54. Bond Polarity d+ d- d+ and d-
Only apparent (partial) charges, much less than a true 1+ or 1- as in ionic bond
Written as: H - Cl
the positive and minus signs (with the lower case delta: ) denote partial charges.
d+ d-
d+ and d-

55. Bond Polarity H Cl Can also be shown:
the arrow points to the more electronegative atom.
electronegativity can also indicate the type of bond that tends to form
H Cl

56. Polar molecules
In small molecules a polar bond tends to make the entire molecule “polar”
areas of “difference”
HCl has polar bonds, thus is a polar molecule.
A molecule that has two poles is called dipole, like HCl

57. Polar molecules
The effect of polar bonds on the polarity of the entire molecule depends on the molecular shape
carbon dioxide has two polar bonds, is linear, and is symmetrical so it’s a nonpolar molecule!

58. Polar molecules
water has two polar bonds and a bent shape; the highly electronegative oxygen pulls the e- away from H so the molecule is very polar!

59. Attractions between molecules (Intermolecular Forces)
They are what make solid and liquid molecular compounds possible.
1. Dispersion forces (Van der Waal’s forces)
weakest of all, caused by motion of e-
increases as # e- increases
Halogens start as gases, fluorine is gas; bromine is liquid; iodine is solid – all in Group 7A.
Although they are all nonpolar molecules, when more e- are present there is more attraction between molecules making them more like a solid.

60. Van der Waals Forces

61. 2. Dipole interactions d+ d- d+ d- H F H F
Occurs when polar molecules are attracted to each other.
Dipole interaction happens in water
positive region of one molecule attracts the negative region of another molecule.
Slightly stronger than dispersion forces.
Opposites attract, but not completely hooked like in ionic solids.
H F
d+ d-
H F
d+ d-

62. 2. Dipole Interactions
d+ d-
d+ d-
d+ d-
d+ d-
d+ d-
d+ d-
d+ d-
d+ d-

63. 3. Hydrogen bonding?
…is the attractive force caused by hydrogen bonded to N, O, F, or Cl
N, O, F, and Cl are very electronegative, so this is a very strong dipole.
The hydrogen partially share with the lone pair in the molecule next to it.
This is the strongest of the intermolecular forces.

64. Why hydrogen?
Hydrogen has a higher electronegativity than metals, but has a lower electronegativity than most nonmetals. It’s the ONLY element with no shielding for its nucleus when involved in a covalent bond!

65. Hydrogen Bonding H O d+ d- H O d+ d-

66. Hydrogen bonding H O H O H O H O H O H O H O

67. Hydrogen Bonding
Chapt. 11.2

68. 4. Molecule – ion attraction
attractive force between the charged end of a molecule and an ion of opposite charge (ex. salt dissolving in water)

69. Why are some chemicals gases, some liquids, some solids?
It depends on the type of forces between the particles!

70. INTERMOLECULAR FORCES HAVE AN EFFECT ON PROPERTIES LIKE:
Viscosity
Solubility
Melting Pt
Boiling Pt

71. AND. . .
Surface Tension
Chemical Reactivity

72. Network solids – solids in which all the atoms are covalently bonded to each other
melts at very high temperatures, or not at all
Diamond does not really melt, but vaporizes to a gas at 3500 oC and beyond
SiC, used in grinding, has a melting point of about 2700 oC

73. Covalent Network Compounds
Some covalently bonded substances DO NOT form discrete molecules.
Diamond, a network of covalently bonded carbon atoms
Graphite, a network of covalently bonded carbon atoms

74. What type of molecule is it? Or are they ions?
If it has an electronegativity difference of:
1.7
0.5
polar covalent
bond
nonpolar covalent
bond
ionic
bond

75. What type of molecule is it? Or are they ions?
nonpolar covalent bond
polar covalent bond
ionic
bond
Must be a Nonpolar molecule
Must be an
Ionic compound
If symmetrical, then
Nonpolar molecule
If asymmetrical, then
polar molecule

76. VSEPR Theory
Valence Shell Electron Pair Repulsion Theory allows us to predict geometry
Molecules take a shape that puts electron pairs as far away from each other as possible.
Lewis structures tell us how the atoms are connected to each other.
The shape of a molecule can greatly affect its properties.
Lone electron pairs take up more space.

77. VSEPR The number of pairs determines The number of atoms determines
bond angles
underlying structure
The number of atoms determines
actual shape

78. Geometry and polarity Linear shape 1800 bond angle
Molecule is symmetrical so the polarity pull is cancelled out. It is nonpolar. ex. BeH2
If the molecule is not symmetrical, it is polar
ex. HF

79. Geometry and polarity Trigonal planar shape
Polarity pull is cancelled out if central atom is bonded to all the same atoms = nonpolar
120º

80. Geometry and polarity Tetrahedral shape
Molecule is symmetrical so the polarity pull is cancelled out if central atom is bonded to all the same atoms = nonpolar

81. Geometry and polarity Bent shape
Polarity pull is not cancelled out, so molecule is a dipole

82. Geometry and polarity Pyramidal shape
Polarity pull is not cancelled out, so molecule is a dipole

83. Polarity and Geometry
Linear O C O O
Bent H H

84. Polarity and Geometry .. F N B F F F F F
Pyramid
Trig. Planar

85. Example: HCN - Hydrogen Cyanide Step 1:
# valence e- molecule WANTS 8 2 18
# valence e- molecule HAS 5 4 1 10
Atom
Nitrogen
Carbon
Hydrogen
SUM: C H

86. HCN - Hydrogen Cyanide Step 2: Calculate # of Bonds
WANTS – HAS = # of bonds 2
18 – 10 = = C
4 bonds H

87. HCN - Hydrogen Cyanide Step 3: Draw It
Start with the “central atom”
Carbon is the central atom; it needs 4 more e-
Nitrogen forms a bond with Carbon
Hydrogen forms a bond with Carbon
What’s wrong with this picture?
1. Only Hydrogen
has the # of e- it wants
2. We predicted 4 bonds
– here there are only 2 H C N

88. H C N HCN - Hydrogen Cyanide We need 2 more bonds
H is full, so bonds must go between C & N
Add one bond, C & N still don’t have 8 e- H C N

89. What type of bond is between C & N?
HCN - Hydrogen Cyanide
We need 2 more bonds
H is full, so bonds must go between C & N
Add one bond, C & N still don’t have 8 e-
Add another bond
Now everyone has the # of e- they want
What type of bond is between C & N?
A triple bond H C N

90. Another way to draw bonds
Use a line to indicate a bond
Each line represents 2 valence e-
This is called a structural formula H N H H C N H

91. Multiple Bonds . . : . . . . :: ::: : : . . . . F O O N N
single bond has one shared electron pair. longest
double bond has two shared electron pairs.
triple bond has three shared electron pairs. shortest
Single Double Triple
. . : F
. .
. . ::
::: O O : : N N
. .
. .
e- config

92. H O H C H H C H H CH2O CH4 H | H - C - H | H O || H-C-H
Molecular Formula
Molecular Formula
CH2O
CH4
Lewis Dot Diagram
Lewis Dot Diagram H O H C H H C H H
Structural Formula
Structural Formula
H | H - C - H | H
O || H-C-H