1. Chemical bonding Why do atoms form bonds? Reason 1: Lower energy state
Energy is always released during bond formation
Bond energy:
The energy required to break a bond
The higher the bond energy, the more stable the bond
Reason 2:
Atoms are most stable when they have a complete valence shell
Noble gases don’t form bonds because they already have a complete valence shell

2. Octet rule:
During bond formation, atoms tend to achieve a complete valence shell (8 e- )
Octet rule can be satisfied in two ways:
Transfer of electrons
from one atom to
another (ionic
bonding)
Sharing of electrons
by two atoms
(covalent bonding)

3. Intramolecular bonds:
Bonds between atoms in a compound, ion, or molecule
Three major types of intramolecular bonds:
Ionic bond:
Transfer of e- from one atom to another, leading to formation of + and – ions
Result in formation of an ionic compound (salt)
Involve a metal cation and a nonmetal anion
e- transferred from valence shell of metal to valence shell of nonmetal
Metal and nonmetal must have an electronegativity difference (END) of 1.7 or greater continued 

4. Ionic Bonding: Click For Animation

5. (+) cation and (–) anion strongly attracted to each other
Ionic bonds very strong (high MP and BP)
Ionic compounds usually water soluble
Conduct electricity in aqueous or molten form
Ionic compounds form ionic crystals; they do not form molecules

6. 2) Covalent bond: Atoms share one or more pair of e- to complete octet
e- are strongly attracted to the nuclei of each atom in the bond
Involve atoms of two nonmetals
END < 1.7
Weaker bond than ionic (lower MP and BP)
Can involve sharing of one, two, or 3 pairs of e- (single, double, or triple bond)
Covalent bond results in the formation
of a molecule
Resulting compound called
covalent or molecular compound

7. Polar covalent bond:
A pair of e- is shared unevenly between two different nonmetals
Element with higher EN attracts e- more strongly
Small partial charge denoted by + or -

8. B) Non-polar covalent bond:
A pair of e- is shared equally by two of the same nonmetal
END is usually zero, but can be 0.4 or less
C) Coordinate covalent bond:
Identical to a polar covalent bond, but both e- are donated by one of the atoms in the bond
Polyatomic ions frequently involve coordinate covalent bonds
Look for an unshared pair of e-

9. Ionic vs. Covalent Bonding: Click For Animation

10. Molecular shapes Valence shell electron pair repulsion (VSEPR):
Electron pairs repel each other to get as far away from each other as possible

11. Different molecular shapes:
Linear
Any molecule with only two atoms must be linear
CO2

12. 2) Bent:
Unshared e- pairs force the atoms out of a straight line
Requires at least three atoms
Note: even when drawn like this, one needs to know that the unshared e- pairs cause bend

13. 3) Pyrimidal:
Unshared e- pair forces atoms into a tented shape
Requires at least four atoms

14. 4) Tetrahedral:
Requires at least five atoms
When four atoms are all bonded to one central atom, the shape they assume is called a tetrahedron

15. Molecular Shapes: Click For Animation

16. Predicting the polarity of covalent molecules:
Bond polarity vs. molecular polarity: Can have a non-polar molecule with polar bonds or a polar molecule with non-polar bonds
Molecular polarity is determined by:
Shape
Charge symmetry

17. SNAP How to determine a molecule’s polarity:
*DOES NOT PERTAIN TO IONIC COMPOUNDS
Step 1) Draw Lewis dot diagram
Step 2) Use VSEPR to determine shape
Step 3) Is charge distributed symmetrically in all directions? If so, molecule is non-polar (doesn’t have + and - ends). If charge is distributed asymmetrically, the molecule is polar
In a two-atom molecule, if the bond is polar then the molecule is polar
SNAP
ymmetrical
onpolar
symmetrical
olar
Click For Animation

18. Significance of polar vs. non-polar molecules:
Will dissolve ionic and other polar substances
Have relatively high MP and BP
Non-polar molecules:
Will dissolve other non-polar substances (like dissolves like)
Have relatively low MP and BP

19. Polar vs. Nonpolar Molecules: Click For Animation

20. D) Network covalent bond
Atoms covalently bound to each other in a giant repeating pattern
Form huge molecules
Strongest of all bonds
Form very hard substances

21. 3) Metallic bond:
Positive metal ions in a “sea of mobile (delocalized) electrons
Since metals have low EN, valence e- are loosely held and free to move from one atom to another
Sea of mobile e- holds all the atoms together tightly, accounting for metal’s higher MP and BP, as well as malleability
Also accounts for metal’s luster and conductivity

22. Metallic Bonding: Click For Animation

23.  1.7 < 1.7 NA High High Low Yes (usually) No Yes No No (usually)
TYPE OF BOND
IONIC
COVALENT
METALLIC
Type of Elements Involved
Electronegativity
Difference
Role of Electrons in the Bond
Melting Point /
Boiling Point
Polar
Non-Polar
Solubility in H2O?
Conductivity of Electricity
General Nature of the Substance
Metal and nonmetal (or polyatomics)
Nonmetals only
Metals only
 1.7
< 1.7 NA
Shared pair between atoms
Shared among all the atoms
Transferred form (+) to (-) ion
High
Very low
High
Low
Yes (usually) No
Yes No
In aqueous or molten form only
No (usually)
Yes
Hard crystal
Gas, liquid, or soft solid
Hard solid

24. Intermolecular forces of attraction:
Attractive forces between two molecules of the same substance or between two different substances
Dipole-dipole attraction:
A polar molecule, because it has + and - poles, is called a dipole. The + end of one molecule is attracted to the - end of another molecule, like opposite poles of a magnet.
continued
Click For Animation

25. Only involves polar covalent molecules
Due to dipole-dipole attraction, polar compounds have higher MP and BP than do non-polar compounds
“Like dissolves like.” Polar substances will dissolve in other polar substances, not in non- polar ones

26. Hydrogen bond: a special type of dipole- dipole attraction
H of one molecule is strongly attracted to the F, O, or N of another molecule
Strongest intermolecular force
When H is bonded to a very small atom with high EN (F, O, or N), one gets a very polar molecule
Molecules with H-bonding have higher BP and MP than other polar substances
continued

27. Hydrogen atom is essentially bound to two atoms at the same time
Responsible for surface tension, meniscus of H2O
Ex: H2O, NH3, HF
Holds together the double-helix of DNA

28. Hydrogen Bonding: Click For Animation

29. Molecule-ion attraction:
The charged ends of a polar molecule are attracted to the charged ions of a salt
The reason most ionic solids dissolve in H2O
Ions become surrounded by H2O (hydrated) and thus dissolve in H2O

30. Molecule-Ion Attraction: Click For Animation

31. Van der Waals forces:
Even in non-polar molecules, random fluctuations in e- distribution can make them temporarily slightly polar
The weakest of all intermolecular forces
Reason for low MP and BP of nonpolar substances
The more e- a molecule has, the greater the attraction
Ex: CH4 vs. C3H8