1. Chapter 3
Chemical Bonds

2. Note: order changed slightly
Will start with ionic bonding and ionic compounds, then move to covalent bonding and molecular compounds, where Lewis dot structures are used
Then will do molecular geometry and VSEPR theory and discuss polarity

3. Key topics for this chapter
Octet rule and how it relates to quantum model of the atom
Differentiating between ionic and covalent bonds
Naming of ionic and molecular compounds
Use of Lewis dot structures and VSEPR theory to determine bonding and geometry of molecular compounds
Bond polarity
Molecule polarity

4. Major themes
Octet rule: valence electrons make chemistry happen, core electrons play small role
Metals react with nonmetals to form ionic compounds
Nonmetals react with nonmetals to form molecular compounds
We learn the rules for writing names and formulas for ionic and molecular compounds
We learn about molecular shape and polarity

7. Octet Rule

8. Octet rule

9. Electron Configurations of Cations and Anions
Of Representative Elements
Na [Ne]3s1
Na+ [Ne]
Metal Atoms ___________ electrons so that cation has a noble-gas outer electron configuration.
Ca [Ar]4s2
Ca2+ [Ar]
Al [Ne]3s23p1
Al3+ [Ne]
H 1s1
H- 1s2 or [He]
Nonmetal Atoms ____________ electrons so that anion has a noble-gas outer electron configuration.
F 1s22s22p5
F- 1s22s22p6 or [Ne]
O 1s22s22p4
O2- 1s22s22p6 or [Ne]
N 1s22s22p3
N3- 1s22s22p6 or [Ne]
8.2

10. Cations and Anions Of Representative Elements+1 +2 +3 -3 -2 -1
8.2

11. Types of Chemical Bonds
According to the Lewis Model
Ionic Bonding
An atom may lose or gain enough electrons to acquire the same electronic structure as its nearest noble gas neighbor (usually 8 valence e-) and become an ion
An ionic bond is the result of the force of attraction between a positive ion (cation) and a negative ion (anion)
Occurs between metals and nonmetals

12. Ionic Bonds

13. Formation of Ionic Bonds
Occur when electrons are transferred from a metal to a nonmetal

15. Ionic Bond in NaCl

16. Ionic Bond in CaCl2

17. Formation of Ionic Bonds
Each atom attains a stable electronic structure
Number of protons/electrons in atoms no longer equal, charged particles result (ions)
Metals lose e-, form + ions (cations)
Nonmetals gain e-, form – ions (anions)

19. A Closer Look at Salt

20. Salt contains a large number of Na+ and Cl- ions

21. Ions pack together tightly into crystalline solids
Strong attractive force between anions and cations holds crystal together

23. Types of Chemical Bonds
According to the Lewis Model
Covalent Bonding
An atom may share electrons with one or more other atoms to acquire a filled valence shell.
A covalent bond is the force of attraction between two atoms that share one or more pairs of electrons.
Occurs between nonmetals

24. Covalent Bonds A sharing of valence electrons between atoms
Usually occurs between nonmetallic elements
Nonmetals need to gain e- in order to attain a stable e- structure
Thus, when they combine, end up sharing valence electrons

25. Covalent Bond
Atom 1
Atom 2
Attractive forces between nucleus of 1 atom and e- from other atom
Repulsive forces between nuclei, electron clouds
Attractive forces stronger, bond forms

26. Covalent Bonds Bohr model of covalent bond By Sharing e-
hydrogen obtains a completely filled 1st energy level
oxygen obtains a completely filled 2nd energy level (stable octet)

27. Lewis, or electron, Dot Diagrams
Show the valence electrons
Consist of element symbol – represents nucleus and core electrons – and dots (valence e-)

28. Elements and Covalent Bonds
Most nonmetallic elements do not exist in nature as individual atoms
e.g. Hydrogen exists as a diatomic molecule, H2
By overlapping 1s orbitals, each H atom attains a stable e- structure

29. Other Molecular Elements
Diatomic Elements (Br2, I2, N2, Cl2, H2, O2, F2)
Hydrogen
All group 7A elements
Oxygen • Nitrogen
BrINCIHOF!!! Memorize it

31. General Rules for Bond Types
Negative complex
ions
Nonmetal
Covalent Bond
Ionic Bond
Metal 31

32. What determines bond type?
Generalization
metal + nonmetal = ionic bond
nonmetal + nonmetal = covalent bond
Reality
Bonding type is on a continuum, from 100% ionic to 100% covalent
100% covalent % ionic

33. Determining Predominant Bond type
Electronegativity is a measure of the tendency for atoms of an element to attract electrons in a chemical bond.
Originated with American chemist Linus Pauling ( ), a 2x Nobel Prize winner from Stanford U
- a relative scale

34. Electronegativity (EN)
Scale ranges from 0.7 to 4.0

36. Electronegativity (EN)
Trends in Periodic table

37. Highly electronegative elements (N, O, F, Cl) are greedy for electrons
Predominant type of bonding (ionic/covalent) determined by differences in electronegativity (EN) between atoms in bond
EN > 1.9, predominantly ionic (metal, nonmetal)
EN 0.5 to 1.9, polar covalent
EN < 0.5, nonpolar covalent
Nonmetal, nonmetal

38. Determining Predominant Bond Type
Look at the electronegativity values of atoms involved in bond
Calculate electronegativity difference (EN)
Draw arrow in direction that e- cloud is pulled (more electronegative atom)
Also use lower case Greek symbol for delta, , along with + or - sign

39. e- rich Cl H d+ d- e- poor Example: Bond between H and Cl
Electronegativity values H= 2.1, Cl = 3.0
EN = = 0.9 = polar covalent bond
e- cloud pulled towards Cl atom = Polar Covalent Bond H Cl
e- rich
electron poor
region
electron rich
region Cl H d+ d-
2.1
3.0
e- poor
Direction e- cloud being pulled
9.5

40. Result of differences in electro-negativity:
More electronegative element has greater share of e- cloud, it is electron rich
Less electronegative element is e- poor
Creation of bond dipoles: + and  -

41. Example of Nonpolar Covalent Bonds
Diatomic elements e.g. H2
Bonds between P and H = =0

42. Bond Character Summary
Nonpolar covalent bond  electrons shared equally
Polar covalent bond  e- not shared equally, more electronegative atom has greater share of e- cloud
Ionic bond – e- transferred from one atom to other, creates a + and – ion