1. Chemical Bonds

2. Atom – the smallest unit of matter “indivisible”
Helium
atom

3. electron shells Atomic number = number of Electrons
Electrons vary in the amount of energy they possess, and they occur at certain energy levels or electron shells.
Electron shells determine how an atom behaves when it encounters other atoms

4. Electrons are placed in shells according to rules:
The 1st shell can hold up to two electrons, and each shell thereafter can hold up to 8 electrons.

5. Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons
C would like to
N would like to
O would like to
Gain 4 electrons
Gain 3 electrons
Gain 2 electrons

6. Why are electrons important?
Elements have different electron configurations
different electron configurations mean different levels of bonding

9. Electron Dot Structures
Symbols of atoms with dots to represent the valence-shell electrons
H He:
          
Li Be  B   C   N   O  : F  :Ne :
       
          
Na Mg  Al  Si  P S :Cl  :Ar :
       

10. Chemical bonds: an attempt to fill electron shells
Ionic bonds –
Covalent bonds –
Metallic bonds

11. Learning Check A. X would be the electron dot formula for
A. X would be the electron dot formula for
1) Na 2) K 3) Al
 
B  X  would be the electron dot formula
1) B 2) N 3) P

12. Two major categories of compounds are ionic and molecular (covalent) compounds.
Ionic compounds are formed when a metal combines with a nonmetal.
Ionic compounds have ionic bonds.
Molecular compounds are formed between two nonmetals.
Molecular compounds have covalent bonds.

13. Regents Question: Which compound contains ionic bonds? NO NO2 CaO

14. Regents Question: þ Nitrogen – nonmetal Oxygen – nonmetal
Which compound contains ionic bonds? NO
NO2
CaO
(4) CO2
Nitrogen – nonmetal
Oxygen – nonmetal
Calcium – metal
Carbon – nonmetal þ

15. Regents Question: Which formula represents an ionic compound? (1) NaCl
(2) N2O
(3) HCl
(4 )H2O

16. Chemical bonds are formed when valence electrons are
transferred from one atom to another (ionic)
shared between atoms (covalent)
mobile within a metal (metallic)

17. IONIC BOND bond formed between two ions by the transfer of electrons

18. Formation of Ions from Metals
Ionic compounds result when metals react with nonmetals
Metals lose electrons to match the number of valence electrons of their nearest noble gas
Positive ions form when the number of electrons are less than the number of protons
Group 1 metals  ion 1+
Group 2 metals  ion 2+
Group 13 metals  ion 3+

19. Formation of Sodium Ion
Sodium atom Sodium ion
Na  – e  Na +
( = Ne)
11 p p+
11 e e-

20. Formation of Magnesium Ion
Magnesium atom Magnesium ion 
Mg  – 2e  Mg2+
(=Ne)
12 p p+
12 e e-

21. Some Typical Ions with Positive Charges (Cations)
Group 1 Group 2 Group 13
H+ Mg2+ Al3+
Li+ Ca2+
Na+ Sr2+
K+ Ba2+

22. Learning Check A. Number of valence electrons in aluminum
1) 1 e ) 2 e- 3) 3 e-
B. Change in electrons for octet
1) lose 3e ) gain 3 e ) gain 5 e-
C. Ionic charge of aluminum
1) ) ) 3+

23. Solution A. Number of valence electrons in aluminum 3) 3 e-
B. Change in electrons for octet
1) lose 3e-
C. Ionic charge of aluminum
3) 3+

24. Learning Check Give the ionic charge for each of the following:
A. 12 p+ and 10 e-
1) 0 2) 2+ 3) 2-
B. 50p+ and 46 e-
1) 2+ 2) 4+ 3) 4-
C. 15 p+ and 18e-
2) ) 3- 3) 5-

25. Ions from Nonmetal Ions
In ionic compounds, nonmetals in groups 15, 16, and 17 gain electrons from metals
Nonmetal add electrons to achieve the octet arrangement
Nonmetal ionic charge:
3-, 2-, or 1-

26. Fluoride Ion     1 - : F  + e : F :     2-7 2-8 (= Ne)
unpaired electron octet
   
: F  e : F :
   
(= Ne)
9 p p+
9 e e-
ionic charge

27. Ionic Bond
Between atoms of metals and nonmetals with very different electronegativity
Bond formed by transfer of electrons
Produce charged ions all states. Conductors and have high melting point.
Examples; NaCl, CaCl2, K2O

29. Ionic Bonds: One Big Greedy Thief Dog!

30. 1). Ionic bond – electron from Na is transferred to Cl, this causes a charge imbalance in each atom. The Na becomes (Na+) and the Cl becomes (Cl-), charged particles or ions.

32. Ionic Bonds: Metals and Non-metals
Metals… lose e-.
Non-metals… gain e-.
They can exchange electrons to form a bond.

33. Metals tend to have low ionization energies, so they lose e- easily.
Non-metals tend to have high electronegativities, so they gain e’ readily.

34. To add to notes…
The two Elements involved in an ionic bond have a difference in electronegativity (E.N.D.) that is greater than or equal to 1.7
Ex: NaCl E.N.D.= 2.3 (How do you find this? Look up electronegativity of each element on Table S and subtract.)
Na = 0.9 Cl = 3.2
3.2 – 0.9 = 2.3

35. Summary of Concepts: Ionic Bonds
Occur between metals (+) and non-metals (-)
Involve a transfer of electrons from the metal to the nonmetal.
The two elements have an electronegative difference of 1.7 or greater
We call ionic compounds “salts”

36. Aim: To identify what covalent bonds are and to compare and contrast them to ionic bonds.
Do Now:
What is an ionic bond?
In order for a bond to be considered ionic, what does the
electronegativity difference between the two elements
have to be?
List two properties of ionic bonds.

37. COVALENT BOND bond formed by the sharing of electrons

38. Covalent Bond
Between nonmetallic elements of similar electronegativity.
Formed by sharing electron pairs
Stable non-ionizing particles, they are not conductors at any state
Examples; O2, CO2, C2H6, H2O, SiC

39. Covalent Bonds

40. Bonds in all the polyatomic ions and diatomics are all covalent bonds

41. Covalent Bonds vs. Ionic Bonds

42. Two Hydrogen Atoms
The valence shells overlap and the electrons are shared making a more stable molecule.

43. Covalent Bonds
Involves SHARING electrons because both elements have high electronegativities.
Sharing of electrons can be equal (non-polar) or unequal (polar)
Usually is between two NON-METALS (ex. H, C, O, N…)
Covalent bonding like Ionic bonding results in a more stable compound, because the atoms involved meet the “octet rule”.

44. Covalent Bonding (cont.)
A “shared” pair of electrons makes a SINGLE BOND (2 total e-).
2 “shared” pairs makes a DOUBLE BOND (4 total e-).
3 “shared” pairs makes a TRIPLE BOND (6 total e-).
We call them MOLECULES.
Covalent bonds are very strong bonds.

45. when electrons are shared equally
NONPOLAR COVALENT BONDS
when electrons are shared equally
H2 or Cl2

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

47. when electrons are shared but shared unequally
POLAR COVALENT BONDS
when electrons are shared but shared unequally
H2O

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

49. - water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.

50. Comparing the properties: compounds with ionic bonds and compounds with covalent bonds.
Properties of molecular compounds
Low melting and boiling points (weak attraction between molecules)
Nonelectrolytes: Do not conduct electricity as solids or when dissolved or molten – no charged particles (ions) to move
Solids are soft
Forms molecules
Properties of ionic compounds
Solids with high melting and boiling points (strong attraction between ions)
Electrolytes: Do not conduct electricity as solids but do when dissolved or molten – ions are charged particles that are free to move
No individual molecules

51. Ionic solids conduct electricity when dissolved or molten
Ionic solids conduct electricity when dissolved or molten Molecular solids do not.
Solution conducts electricity
Solution doesn’t conduct electricity
Ionic Solid dissolved in water
Molecular Solid dissolved in water

52. Regents Question:
Which of the following solids has the highest melting point?
(1) H2O(s)
(2) Na2O(s)
(3) SO2 (s)
(4) CO2 (s)

53. Regents Question:
Which of the following solids has the highest melting point?
(1) H2O(s)
(2) Na2O(s)
(3) SO2 (s)
(4) CO2 (s) þ

54. Regents Question:
Testing of an unknown solid shows that it has the properties listed below.
(1) low melting point (2) nearly insoluble in water (3) nonconductor of electricity (4) relatively soft solid
State the type of bonding that would be expected in the particles of this substance.
Explain in terms of attractions between particles why the unknown solid has a low melting point.
Explain why the particles of this substance are nonconductors of electricity.

55. Regents Question: Covalent
Testing of an unknown solid shows that it has the properties listed below.
(1) low melting point (2) nearly insoluble in water
(3) nonconductor of electricity
(4) relatively soft solid
State the type of bonding that would be expected in the particles of this substance.
Explain in terms of attractions between particles why the unknown solid has a low melting point.
Explain why the particles of this substance are nonconductors of electricity.
Covalent
The attraction between particles is weak because there are no charged particle.
Molecular substances are non-electrolytes – they do not form ions.

56. When nonmetals combine with nonmetals, they share electrons
When nonmetals combine with nonmetals, they share electrons. The attraction of two atoms for a shared pair makes a covalent bond.
Electrons are always shared in pairs.
Sharing electrons fills the valence shell with 8 electrons (2 for hydrogen.)
Hydrogen chloride water ammonia methane

57. Regents Question:
Which type of chemical bond is formed between two atoms of bromine?
Metallic
(2) Hydrogen
(3) ionic
(4) covalent

58. Regents Question
Which type of chemical bond is formed between two atoms of bromine?
Metallic
(2) Hydrogen
(3) ionic
(4) covalent þ

59. In a multiple covalent bond, more than one pair of electrons are shared between two atoms.
Diatomic oxygen has a double bond O=O (2 shared pairs) because oxygen needs 2 electrons to fill its valence shell
Diatomic nitrogen has a triple bond NN (3 shared pairs) because nitrogen needs 3 electrons to fill its valence shell
Carbon dioxide has two double bonds

60. Regents Question: þ Which molecule contains a triple covalent bond?
(4) Cl 2 þ

61. Molecular polarity can be determined by the shape of the molecule and the distribution of charge.
Possible shapes
Linear (X2 HX CO2)
Bent (H2O)
Pyramidal (NH3)
Tetrahedral (CH4 CCl4)
A polar molecule is called a dipole. It has a positive side and a negative side – uneven charge distribution.

62. Symmetrical molecules are not dipoles.
Symmetrical (nonpolar) molecules include CO2 , CH4 , and diatomic elements. ..
Symmetrical molecules are not dipoles.

63. Asymmetrical (polar) molecules include HCl, NH3 , and H2 O. (5.2l)
The negative side of the molecule is the side that has the atom with the higher electronegativity.

64. Physical properties of substances can be explained in terms of chemical bonds and intermolecular forces. These properties include conductivity, malleability, solubility, hardness, melting point, and boiling point.

65. The stronger the intermolecular forces, the higher the boiling points and melting points.
Strongest
Ionic Solids
Molecules with Hydrogen bonds
Polar molecules
Nonpolar molecules
Weakest
For nonpolar molecules, the greater the mass, the greater the force of attraction.

66. Regents Question:
The table below shows the normal boiling point of four compounds.
Compound Normal Boiling Point (°C)
HF (l)
CH3Cl (l) –24.2
CH3F (l) –78.6
HCl (l) –83.7
Which compound has the strongest intermolecular forces?
(1) HF(l) (2) CH3Cl(l) (3)CH3F(l) (4)HCl(l)

67. Regents Question:
The table below shows the normal boiling point of four compounds.
Compound Normal Boiling Point (°C)
HF (l)
CH3Cl (l) –24.2
CH3F (l) –78.6
HCl (l) –83.7
Which compound has the strongest intermolecular forces?
(1) HF(l) (2) CH3Cl(l) (3)CH3F(l) (4)HCl(l) þ

68. Electronegativity indicates how strongly an atom of an element attracts electrons in a chemical bond.

69. Electronegativity values are assigned according to arbitrary scales
Fluorine is assigned the value 4.0 – the highest of any element
Nonmetals have high electronegativity – they want to attract electrons so they can fill their valence shell
Metals have low electronegativity – they want to lose electrons to get rid of their valence shell

70. Regents Question: (1) electronegativity (2) ionization energy
The strength of an atom’s attraction for the electrons in a chemical bond is the atom’s
(1) electronegativity
(2) ionization energy
(3) heat of reaction
(4) heat of formation

71. Regents Question:
The strength of an atom’s attraction for the electrons in a chemical bond is the atom’s
(1) electronegativity
(2) ionization energy
(3) heat of reaction
(4) heat of formation þ

72. The electronegativity difference between two bonded atoms is used to assess the degree of polarity in the bond.
Polar covalent bonds form between two different nonmetals
Polar bonds have a negative side and a positive side
The electrons are attracted more to the atom with the higher electronegativity.
The atom with the higher electronegativity is the negative side of the bond.

73. RECALL!
When the electronegativity difference between two elements is greater than or equal to 1.7, it is an IONIC bond.
When the electronegativity difference between two elements is less than 1.7, it is a COVALENT bond.
Complete the worksheet!

74. Regents Question:
Which of these formulas contains the most polar bond?
(1) H–Br
(2) H–Cl
(3) H–F
(4) H–I

75. Regents Question:
Which of these formulas contains the most polar bond?
(1) H–Br
(2) H–Cl
(3) H–F
(4) H–I þ

76. Three types of bonds
Ionic bonds– transfer of electrons- occur between a metal and a nonmetal
Polar bonds– unequal sharing- occur between two different nonmetals
Nonpolar bonds– equal sharing- occur between two of the same nonmetals

77. Electron-dot diagrams (Lewis structures) can represent the valence electron arrangement in elements, compounds, and ions.
atom ion molecular compound
ionic compound

78. Magnesium atom Magnesium ion
When metals lose electrons to form ions, they lose all their valence electrons. The Lewis Dot Structure of a metal ion has no dots. The charge indicates how many electrons were lost.
Magnesium atom Magnesium ion

79. When nonmetals gain electrons, they fill up their valence shell with a complete octet (except hydrogen.) The ion is placed in brackets with the charge outside the brackets.

80. The formula for magnesium fluoride is MgF2
A (+) metal ion is attracted to a (–) nonmetal ion (opposites attract) forming an ionic compound. We can use Lewis dot structures to represent ionic compounds.
The formula for magnesium fluoride is MgF2

81. Regents Question:
Draw the electron-dot (Lewis) structure of an atom of calcium.
Draw the electron-dot (Lewis) structure of an atom of chlorine.
Draw the electron-dot (Lewis) structure of calcium chloride.

82. Regents Question:
Draw the electron-dot (Lewis) structure of an atom of calcium.
Draw the electron-dot (Lewis) structure of an atom of chlorine.
Draw the electron-dot (Lewis) structure of calcium chloride.

83. Regents Question:
Draw an electron-dot diagram for each of the following substances:
A. calcium oxide (an ionic compound)
B. hydrogen bromide
C. carbon dioxide

84. Regents Question:
Draw an electron-dot diagram for each of the following substances:
A calcium oxide (an ionic compound)
B hydrogen bromide
C carbon dioxide

85. Polyatomic ions are groups of atoms covalently bonded together that have a negative or positive charge.

86. Polyatomic ions are held together by covalent bonds but form ionic bonds with other ions.+
Ionic bond H -
Covalent bonds
H N H Cl H

87. METALLIC BOND bond found in metals; holds metal atoms together very strongly

88. The bonds holding metals together in their crystal lattice are called metallic bonds.
All metals have metallic bonds
“Positive ions immersed in a sea of mobile electrons”
Bonds are between Kernels, leaving the valence electrons free to move from atom to atom
Mobile electrons give metals the ability to conduct electricity

89. Metallic Bond Formed between atoms of metallic elements
Electron cloud around atoms
Good conductors at all states, lustrous, very high melting points
Examples; Na, Fe, Al, Au, Co

90. Metallic Bonds: Mellow dogs with plenty of bones to go around.

91. Regents Question: Metallic bonding occurs between atoms of (1) sulfur
(2) copper
(3) Fluorine
(4) carbon

92. Regents Question: þ Metallic bonding occurs between atoms of
(1) sulfur
(2) copper
(3) Fluorine
(4) carbon þ

93. Regents Question:
The high electrical conductivity of metals is primarily due to
(1) high ionization energies
(2) filled energy levels
(3) mobile electrons
(4) high electronegativities

94. Regents Question: 01/03 #15
The high electrical conductivity of metals is primarily due to
(1) high ionization energies
(2) filled energy levels
(3) mobile electrons
(4) high electronegativities þ

95. Regents Question: Which substance contains metallic bonds? (1) Hg(l)
(2) H2O(l)
(3) NaCl(s)
(4)C6H12O6(s)

96. Regents Question: þ Which substance contains metallic bonds? (1) Hg(l)
(2) H2O(l)
(3) NaCl(s)
(4)C6H12O6(s) þ

97. Metallic Bond, A Sea of Electrons

98. Metals Form Alloys Metals do not combine with metals. They form
Alloys which is a solution of a metal in a metal.
Examples are steel, brass, bronze and pewter.

99. Regents Question:
A chemist performs the same tests on two homogeneous white crystalline solids, A and B. The results are shown in the table below.
The results of these tests suggest that (1) both solids contain only ionic bonds (2) both solids contain only covalent bonds (3) solid A contains only covalent bonds and solid B contains only ionic bonds (4) solid A contains only ionic bonds and solid B contains only covalent bonds

100. Regents Question:
A chemist performs the same tests on two homogeneous white crystalline solids, A and B. The results are shown in the table below.
The results of these tests suggest that (1) both solids contain only ionic bonds (2) both solids contain only covalent bonds (3) solid A contains only covalent bonds and solid B contains only ionic bonds (4) solid A contains only ionic bonds and solid B contains only covalent bonds þ

101. Regents Question:
Each molecule listed below is formed by sharing electrons between atoms when the atoms within the molecule are bonded together.
Molecule A: Cl2 Molecule B: CCl4 Molecule C: NH3
Draw the electron-dot (Lewis) structure for the NH3 molecule.
Explain why CCl4 is classified as a nonpolar molecule.
Explain why NH3 has stronger intermolecular forces of attraction than Cl2 .
Explain how the bonding in KCl is different from the bonding in molecules A, B, and C.

102. Regents Question:
Draw the electron-dot (Lewis) structure for the NH3 molecule.
Explain why CCl4 is classified as a nonpolar molecule.
Explain why NH3 has stronger intermolecular forces of attraction than Cl2 .
Explain how the bonding in KCl is different from the bonding in molecules A, B, and C.
It is symmetrical. There is an even charge distribution around the molecule.
Ammonia has hydrogen bonds, chlorine is nonpolar.
KCl is ionic and molecules A, B and C are molecular with covalent bonds.