1. Northern Kentucky University
Lecture Presentation
Chapter 6
How Atoms Bond
Bradley Sieve
Northern Kentucky University
Highland Heights, KY

2. 6.1 Electron-Dot Structures
Valence Electrons
Outermost electrons of an atom
Valence Shell
The outer shell containing electrons
Electron-Dot Structure
Convenient notation showing the valence electrons

3. 6.1 Electron-Dot Structures
Model showing the valence electron arrangements within an atom
Explains ionic and covalent bonding

4. 6.1 Electron-Dot Structures
Important information in the dot-diagram
Number of valence electrons
Number of paired and unpaired electrons

5. 6.1 Electron-Dot Structures
Nonbonding Electron Pairs
Nonbonding electron pairs do not normally form bonds
Unpaired Electrons
Have a strong tendency to form bonds
Become paired as they form bonds

6. 6.1 Electron-Dot Structures
Electron Spin
Causes of electron pairing
Two types of spin
Clockwise
Counterclockwise

7. Concept Check
Where are valence electrons located? Why are they important?

8. Concept Check
Valence electrons are located in the outermost occupied shell of an atom. They are important because they play a leading role in determining the chemical properties of the atom.

9. 6.2 Atoms Can Lose or Gain Electrons to Become Ions
Electrons can gain or lose electrons
Unequal number of electrons and protons results in a charge
Atom with a charge is called an ion
A positive charge is seen when an atom has more protons, called a cation
A negative charge is seen when an atom has more electrons, referred to as an anion
Superscripts are used to denote charges

10. 6.2 Atoms Can Lose or Gain Electrons to Become Ions

11. 6.2 Atoms Can Lose or Gain Electrons to Become Ions

12. 6.2 Atoms Can Lose or Gain Electrons to Become Ions
Atoms tend to lose or gain electrons to reach a noble gas shell model
Atom’s model matches a noble gas’s model
Atoms with few electrons tend to lose electrons
Atoms with many electrons tend to gain electrons

13. 6.2 Atoms Can Lose or Gain Electrons to Become Ions

14. Concept Check
What type of ion does the magnesium atom, Mg, tend to form?

15. Concept Check
The magnesium atom (atomic number 12) is found in group 2 and has two valence electrons to lose. Therefore, it tends to form the 2+ ion.

16. 6.2 Atoms Can Lose or Gain Electrons to Become Ions
Additional notes for noble gas shell model
Noble gas atoms do not tend to form ions
Already have filler outermost shells
Noble gas shell model works well for groups 1, 2, and 13–18
Groups 3–12 are more complicated

17. 6.2 Atoms Can Lose or Gain Electrons to Become Ions
Molecules can form ions
Normally occurs with the addition of an H+
Remember H+ is simply a proton
Referred to as polyatomic ions

18. 6.2 Atoms Can Lose or Gain Electrons to Become Ions
Common Polyatomic Ions

19. 6.3 Ionic Bonds Result from a Transfer of Electrons
When an atom that tends to lose electrons pairs with one that tends to gain electrons, an ionic bond is formed
Ionic bond is the electric force of attraction between two oppositely charged ions

20. 6.3 Ionic Bonds Result from a Transfer of Electrons

21. 6.3 Ionic Bonds Result from a Transfer of Electrons
Ionic Compound
A compound containing ions
Typically form with elements from different sides of the periodic table
Metals tend to exhibit positive charges
Nonmetals tend to exhibit negative charges
Positive and negative charges must balance
Processes properties different from those of the original elements

22. 6.3 Ionic Bonds Result from a Transfer of Electrons

23. 6.3 Ionic Bonds Result from a Transfer of Electrons

24. Concept Check
What is the chemical formula for the ionic compound magnesium oxide?

25. Concept Check
Because magnesium is a group 2 element, you know a magnesium atom must lose two electrons to form a Mg2+ ion. Because oxygen is a group 16 element, an oxygen atom gains two electrons to form an O2− ion. These charges balance in a one-to-one ratio, so the formula for magnesium oxide is MgO.

26. 6.3 Ionic Bonds Result from a Transfer of Electrons
Ionic Crystal
Three-dimensional arrangement of ions in an ionic compound
Give rise to macroscopic crystal shapes

27. 6.4 The Electrons of Metallic Bonds Are Loosely Held
Electrons are loosely held and easily dislodged
Electrons flow freely through metal ions

28. 6.4 The Electrons of Metallic Bonds Are Loosely Held
Alloy
Two or more metals held together with metallic bonding
White gold is one example of an alloy

29. 6.4 The Electrons of Metallic Bonds Are Loosely Held
Metals in Nature
Native metal—metal found pure in nature
Most are found as compounds
Ores
Geologic deposits containing high concentrations of metal-containing compounds

30. 6.4 The Electrons of Metallic Bonds Are Loosely Held

31. 6.5 Covalent Bonds Result from a Sharing of Electrons
Bond formed through sharing of valence electrons

32. 6.5 Covalent Bonds Result from a Sharing of Electrons
Covalent Compound
Substance held together by covalent bonds
A molecule is the fundamental unit of covalent compounds

33. 6.5 Covalent Bonds Result from a Sharing of Electrons
Electron-dot structures for covalent compounds
Nonbonding pairs are pairs on single atom
Bonding pairs are shared between two atoms

34. 6.5 Covalent Bonds Result from a Sharing of Electrons
Primarily in nonmetal pairings
H tends to form covalent compounds
Line represents a bonding pair

35. 6.5 Covalent Bonds Result from a Sharing of Electrons

36. 6.5 Covalent Bonds Result from a Sharing of Electrons
Diamond
Unusual C covalent compound
Each carbon is bound to four other carbons
Very strong and rigid structure

37. Concept Check
How many electrons make up a covalent bond?

38. Concept Check
Two—one from each participating atom

39. 6.5 Covalent Bonds Result from a Sharing of Electrons
Multiple Bonds
When more than two electrons are shared
Double bond is sharing of four electrons
Triple bond is sharing of six electrons

40. 6.5 Covalent Bonds Result from a Sharing of Electrons
Covalent Bonding in Polyatomic Ions
Comprised of covalent bonding and an overall charge

41. 6.6 Valence Electrons Determine Molecular Shape
Valence-shell electron-pair repulsion
Also called VSEPR
Electron pairs arrange so they are as far apart as possible
Result of simple electrostatic repulsions
Must consider three-dimensional space

42. 6.6 Valence Electrons Determine Molecular Shape
Methane shape (CH4)

43. 6.6 Valence Electrons Determine Molecular Shape
Methane shape (CH4)

44. 6.6 Valence Electrons Determine Molecular Shape

45. 6.6 Valence Electrons Determine Molecular Shape
Molecular shape is defined by the substituent atoms
Substituent atom is an atom or a lone pair on the central atom
Two steps to finding shape
Position all substituents around central atom
Ignore nonbonding pairs and determine shape

46. 6.6 Valence Electrons Determine Molecular Shape

47. Concept Check
What is the shape of a chlorine trifluoride molecule, ClF3?

48. Concept Check
In the shape of chlorine trifluoride, all four atoms are in the same plane. They form a triangle having a fluorine atom at each corner and the chlorine atom sitting at the midpoint on one side.

49. 6.7 Polar Covalent Compounds―Uneven Sharing of Electrons
Sharing of electrons is not always equal
Uneven sharing leads to polar covalent bonds
Separation of charges is called a dipole

50. 6.7 Polar Covalent Compounds―Uneven Sharing of Electrons
Electronegativity
Ability of an atom to tug on bonding electrons
The greater the electronegativity, the greater its ability to pull electrons toward itself
Highest values in upper right of the periodic table

51. 6.7 Polar Covalent Compounds―Uneven Sharing of Electrons

52. 6.7 Polar Covalent Compounds―Uneven Sharing of Electrons
Types of Covalent Bonds
Nonpolar bond
The two atoms exhibit the same electronegativity
Does not exhibit a dipole
Polar bond
The two atoms differ in electronegativity
Does exhibit a dipole

53. 6.7 Polar Covalent Compounds―Uneven Sharing of Electrons

54. 6.8 Molecular Polarity―Uneven Distribution of Electrons
Polarity in molecules depends on the three-dimensional shape of the molecule
Must consider both strength of dipole and direction of dipole
If the dipoles cancel completely, molecule is nonpolar; if not, then molecule is polar

55. 6.8 Molecular Polarity―Uneven Distribution of Electrons
CO2 is nonpolar

56. 6.8 Molecular Polarity―Uneven Distribution of Electrons
BF3 is nonpolar

57. 6.8 Molecular Polarity―Uneven Distribution of Electrons
When forces are unbalanced,
the molecule is polar

58. 6.8 Molecular Polarity―Uneven Distribution of Electrons
Water is polar

59. 6.8 Molecular Polarity―Uneven Distribution of Electrons
Polar molecules can be thought of as “sticky”
The different charges are attracted to each other
The stronger the interactions, the higher the boiling and melting points

60. 6.8 Molecular Polarity―Uneven Distribution of Electrons
Water molecules attract one another because each contains slightly positive and slightly negative sides

61. 6.8 Molecular Polarity―Uneven Distribution of Electrons