1. Chemical Bonding

2. Chemical Bonding
Chemical bonding refers to the attractive forces that hold atoms together in compounds.

3. There are two major classes of bonding:
Ionic bonding results from electrostatic interactions among ions, which often results from the net transfer of one or more electrons from one atom to another
-Atoms that lose electrons form positive
ions called cations.
-Atoms that gain electrons form negative
ions called anions.

4. There are two major classes of bonding (continued):
Covalent bonding results from sharing one or more electron pairs between two atoms
-Atoms that share electron pairs equally
are referred to as nonpolar covalent
bonds.
-Atoms that share electron pairs unequally
are referred to as polar covalent bonds.

5. All bonds between atoms of different elements have at least some degree of both ionic and covalent character.
Compounds containing predominantly ionic bonding are called ionic compounds.
Compounds that are held together mainly by covalent bonds are called covalent compounds.
Polyatomic ions are groups of covalently bonded atoms that together form ionic bonds with other atoms.
Some nonmetallic elements, such as H2, N2, O2, F2, Cl2, Br2, I2 also involve covalent bonding.
Many molecules found in nature consist of covalently bonded carbon-carbon or carbon-hydrogen bonds or both. These compounds are classified as organic compounds.

6. Properties of Ionic and Covalent Compounds
Ionic Compounds
Crystalline solids
High melting points (>400oC)
Soluble in polar solvents such as water
Molten compounds conduct electricity
Aqueous solutions conduct electricity
Usually formed between a metal and a nonmetal.
Covalent Compounds
Gases, Liquids, or soft solids
Low melting points (<300oC)
Insoluble in polar solvents such as water
Most are soluble in nonpolar solvents such as hexane and carbon tetrachloride
Liquid, molten, and aqueous solutions do not conduct electricity
Usually formed between nonmetals

7. Representing Compounds
There are several methods used in representing compounds:
Chemical formula -gives the number of atoms of each type in the compound
-Molecular formula gives the actual number of
atoms of each type
-Empirical formula gives the simplest ratio of
Structural formula -shows the order in which the atoms in a compound are connected

8. Naming Simple Compounds
Binary Ionic Compounds (Type I)
1. The cation is always named first and the anion second.
2. A monatomic cation takes its name from the name of the element.
3. A monatomic anion is named by taking the root of the element name and adding –ide.

9. What is the name of AlCl3? Aluminum trichloride Aluminum chloride10
Aluminum trichloride
Aluminum chloride
Aluminum chlorine
Aluminide chloride 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

10. Naming Simple Compounds
Binary Ionic Compounds (Type II)- Metals that can form more than one positive ion can form more than one type of compound with a given anion.
1. The charge on the metal ion must be specified by using a Roman numeral following the cation name.
2. The anion is named the same as with the Type I compounds.

11. What is the name of CuCl? Copper chloride Copper (I) chloride10
Copper chloride
Copper (I) chloride
Copper (II) chloride
Copper chlorine 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

12. What is the name of HgO? Mercury oxide Mercury (I) oxide10
Mercury oxide
Mercury (I) oxide
Mercury (II) oxide
Mercury oxygen 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

13. What is the name of Fe2O3? Iron oxide Iron (I) oxide Iron (II) oxide10
Iron oxide
Iron (I) oxide
Iron (II) oxide
Iron (III) oxide 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

14. What is the name of MnO2? Manganese oxide Manganese (I) oxide10
Manganese oxide
Manganese (I) oxide
Manganese (II) oxide
Manganese (IV) oxide 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

15. What is the name of GaI3? Gallium iodide Gallium (I) iodide10
Gallium iodide
Gallium (I) iodide
Gallium (II) iodide
Gallium (III) iodide 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

16. Naming Simple Compounds
Ionic Compounds with Polyatomic Ions
1. Polyatomic ions have specific names which must be memorized.
2. The other ion is named in the same manner as the Type I or Type II compounds.

17. What is the name of Na2SO4? Sodium sulfide Sodium sulfate10
Sodium sulfide
Sodium sulfate
Sodium sulfite
Sodium (II) sulfate 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

18. What is the name of Fe(NO3)3?10
Iron nitrate
Iron (III) nitrate
Iron nitrite
Iron (III) nitrite 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

19. What is the name of CuCO3? Copper carbonate Copper (I) carbonate10
Copper carbonate
Copper (I) carbonate
Copper (II) carbonate
Copper (III) carbonate 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

20. What is the name of NaOCl?10
Sodium oxygen chloride
Sodium hypochlorite
Sodium chlorite
Sodium chlorate 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

21. Naming Simple Compounds
Binary Covalent Compounds (Type III)
1. The first element in the formula is named first, using the full element name.
2. The second element is named as if it were an anion.
3. Prefixes are used to denote the numbers of atoms present.

22. Binary Covalent Compounds
Prefixes Number Indicated
Mono Di
Tri
Tetra
Penta
Hexa
Hepta
Octa
Nona
Deca

23. What is the name of PCl5? Phosphorus chloride Phosphorus (V) chloride10
Phosphorus chloride
Phosphorus (V) chloride
Monophosphorus pentachloride
Phosphorus pentachloride 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

24. What is the name of N2O3? Nitrogen oxide Nitrogen (II) oxide10
Nitrogen oxide
Nitrogen (II) oxide
Nitrogen trioxide
Dinitrogen trioxide 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

25. What is the name of Nb2O5? Diniobium pentaoxide Niobium oxide10
Diniobium pentaoxide
Niobium oxide
Niobium (II) oxide
Niobium (V) oxide 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

26. What is the name of Ti(NO3)4?10
Titanium nitrate
Titanium tetranitrate
Titanium (IV) nitrate
Titanium (XII) nitrate 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

27. Writing Formulas
Given the name of a compound, the following rules are followed when writing the formula:
1. For ionic compounds, the sum of the charges must equal zero. Subscripts are added as needed in order to follow this rule.
2. For covalent compounds, subscripts are added according to the numerical prefixes given.

28. Energy of Chemical Bonds
Bond energy- the energy required to break a bond.
Bond energy can be used to indicate the strength of a bonding interaction.
Ionic bonds form when an atom loses electrons relatively easily to an atom that has a high electron affinity.
Ionic compounds result when a metal reacts with a nonmetal.

29. Coulomb’s Law
Coulomb’s law can be used to calculate the energy of interaction between a pair of ions.
E = 2.31 x J . nm (Q1Q2/ r)
E is energy in joules, r is the radius between the ion centers in nanometers, and Q1 and Q2 are the numerical ion charges.
Example: the distance between Na+ and Cl- ions is nm. What is the ionic energy per pair of ions?
-8.37 x J
A negative sign indicates an attractive force. (The ion pair has lower energy than the separated ions and is therefore more stable).
Coulomb’s law can also be used to calculate the repulsive force between two like charged ions. In this case, the sign will be positive.

30. Energy Effects in Binary Ionic Compounds
Lattice energy is the change in energy that takes place when separated gaseous ions are packed together to form an ionic solid. (Energy that is released when an ionic solid forms from its ions).
If energy is released, it represents an exothermic process. (Energy will have a negative sign).

31. Lattice Energy Calculations
A modified form of Coulomb’s Law can be used to calculate lattice energy.
Lattice energy = k(Q1Q2 / r)
K is a constant that depends on the structure of the solid and electron configuration of the ions, Q1 and Q2 are the charges on ions, and r is the distance between the nuclei of the ions.

32. Which compound has the most exothermic lattice energy?10
NaCl
KCl 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

33. Which compound has the most exothermic lattice energy?10
LiF
LiCl 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

34. Which compound has the most exothermic lattice energy?10
Mg(OH)2
MgO 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

35. Which compound has the most exothermic lattice energy?10
Fe(OH)2
Fe(OH)3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

36. Which compound has the most exothermic lattice energy?10
NaCl
Na2O 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

37. Which compound has the most exothermic lattice energy?10
MgO
BaS 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

38. Which compound has the most exothermic lattice energy?10
MgO
NaF 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

39. Covalent Bonding Electrons are shared between the nuclei of two atoms.
Polar covalent bonding occurs when there is unequal sharing between the atoms.
Unequal sharing results from electronegativity differences between atoms.
Electronegativity is the ability of an atom in a molecule to attract shared electrons to itself.
Electronegativity increases bottom to top and left to right across the periodic table.
The fractional charge that results is called a dipole moment.
The dipolar character of a molecule is represented by an arrow pointing to the negative charge center.
See page 334 for table of electronegativities.

40. Which of the following pairs of elements forms a nonpolar covalent bond?10
H-H
S-H
O-H
F-H
Cl-H 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

41. H-H, O-H, Cl-H, S-H, F-H F-H, Cl-H, O-H, S-H, H-H
Select the answer choice that lists the pairs of elements in order of increasing polarity. 10
H-H, O-H, Cl-H, S-H, F-H
F-H, Cl-H, O-H, S-H, H-H
H-H, O-H, S-H, Cl-H, F-H
H-H, S-H, Cl-H, O-H, F-H 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

42. Polar and Nonpolar Molecules
A molecule is nonpolar if the dipoles cancel (opposed bond polarities cancel out).
This occurs when the bonds are symmetrically arranged within the molecule.
A molecule is polar if the dipoles do not cancel out.

43. Which of the following molecules is nonpolar?10
H2O
CH4
CH3Cl
HCl 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

44. Which of the following molecules is polar?10
CO2 CO
C6H6 O2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

45. Types of Covalent Bonds
Single bond-One pair of electrons is shared between atoms
Double bond-two pairs of electrons are shared between atoms
Triple bond-three pairs of electrons are shared between atoms

46. Bond Energy and Bond Length
Bond energy increases as follows:
single bond < double bond < triple bond
Bond length increases as follows:
triple bond < double bond < single bond

47. Bonding Models Localized Electron Bonding Model
Molecules consist of lone pairs and bonding pairs of electrons
VSEPR Model
The structure around a given atom is determined principally by minimizing electron pair repulsions. (Bonding and nonbonding pairs are positioned as far apart as possible)

48. Lewis Structures
The Lewis structure shows how the valence electrons are arranged among the atoms in a molecule.
For the formation of a stable compound, the atoms should achieve noble gas configuration.

49. Steps for Writing Lewis Structures
Find the total number of electrons needed if each element had a complete octet. (remember hydrogen only needs two valence electrons to be stable)
Determine the total number of valence electrons available.
Find the difference between what is needed and what is available in order to determine the number of electrons shared.
Every two electrons shared represents one bond.

50. Give the Lewis structure for each of the following.
HCl
NO+
NH3
HCN
CO2

51. Exceptions to the Octet Rule
Some compounds form in which one or more atoms will have fewer than 8 electrons in the outer level (incomplete octet)
Example: BF3
Other compounds form in which one atom may have more than 8 electrons in the outer level (Exceeds the octet rule)
Example: SF6

52. Resonance
Resonance is invoked when more than one valid Lewis structure can be written for a molecule.
The resulting electron structure of the molecule is given by an average of these resonance structures.
This is supported by experimental observations in which the bond lengths and strengths are between those expected if the bonds were single and/or double.

53. Formal Charge
Molecules that exceed the octet rule can often have many nonequivalent Lewis structures, all which obey the rules for writing Lewis structures.
Through the determination of formal charges, the Lewis structures can be evaluated as to which best describes the bonding in the molecule.

54. Rules Governing Formal Charge
Determine the sum of the lone pair electrons and one-half of the shared electrons. This is the number of valence electrons assigned to the atom.
Subtract the number of valence electrons assigned to the atom from the valence electrons on the free , neutral atom.
The sum of the formal charges must equal the overall charge on the ion or molecule.
If nonequivalent structures exist, those with formal charges closest to zero and with any negative formal charges on the most electronegative atoms are considered the best description of the bonding.

55. Sigma bonds

56. Pi bonds
Triple Bond
Double bond