1. The Periodic Table and Chemical Bonding Lesson 4
UNIT VIII
The Periodic Table and Chemical Bonding
Lesson 4

2. Review
Going DOWN a FAMILY size of atom increases and distance between valence electrons and nuclei increase
Going ACROSS a PERIOD properties are affected by differing valence, nuclear charge and charge on the species
One more piece of info on trends…Electronegativity!

3. Hey! I find your electrons attractive!
Electronegativity
Electronegativity – the tendency of an atom to attract electrons from a neighbouring atom.
Get lost, loser!
Hey! I find your electrons attractive!

4. VIII.3 CHEMICAL BONDING
ELECTRONEGATIVITY --- tendency of the atom to attract electrons from a neighbouring atom
Going from left to right across the periodic table the electronegativity of the atoms will __________________
Going down a family of the periodic table the electronegativity of the atoms will _____________________

5. Electronegativity increases as you move from left to right.
Electronegativity decreases as you move down each column.

6. Ex: Which is more electronegative: K or Br? Pb or S?

7. Electronegativity & Ionization Energy(IE)
If an atom has high electronegativity, it strongly attracts e- from a neighbouring atom (also difficult to remove its own e- so it has high IE)
If an atom has low electronegativity, it has little attraction to the electrons of neighbouring atoms (easy to remove e- so low IE)
Electronegativity and IE have the same trend on PT!

8. SUMMARY OF PERIODIC TABLE TRENDS:

9. Size of ions vs size of a neutral atom

10. SIZE OF IONS vs NEUTRAL atoms
 Li → e Li+
1 valence e- closed shell
Positive ions are smaller than the corresponding neutral atom
Why??
(fewer electrons, so less repulsion between them).

11. SIZE OF IONS vs NEUTRAL atoms
Cl + e- → Cl-
7 valence e- closed shell
Negative ions are larger than the corresponding neutral atom
Why??
(more electrons, so more repulsion between them).

12. Types of chemical bonds
Ionic and covalent

13. Types of Chemical Bonds
A. Ionic Bonding:
Ionic Bond –

14. VIII.3 CHEMICAL BONDING Ex: Na + Cl Ex: Ca + O
*The greater the distance between the charges, the smaller the attraction!

15. NaCl
Crystal Lattice

16. Li F
An F Atom
A Li Atom - + Li F
A Li+ Ion
An F- Ion

17. The melting points of some Ionic Compounds are as follows:
NaF oC KCl oC LiCl oC
These high melting points are experimental evidence that Ionic Bonds are VERY STRONG. (Hard to break just by heating).

18. Ionic Bonds
IONIC BONDS are VERY STRONG, so compounds held together by ionic bonds have HIGH MELTING TEMPERATURES
Think about it…
*When there is a smaller radius, there is a stronger/weaker bond
*When there is a larger charge, there is a stronger/weaker bond

19. Covalent Bonds

20. Covalent Bonds
b. Covalent Bonding:
 Covalent Bond:
Octet Rule:

21. In Covalent bonds, electrons are Shared

22. VIII.3 CHEMICAL BONDING Ex: Cl – Cl
Non-mental bonds to a nonmetal (SHARE e-)
Covalent bonds are STRONG, but the bonds between molecules are WEAK
ex: Cl2 molecules bonded together

23. Covalent Bonds
Polar Covalent
Non-polar Covalent
HCl
Cl2

24. Diamonds are “forever”!
diamond structure
Diamonds are “forever”!

25. Covalent bonds are also very strong!
Some melting points of Network Solids:
Diamond (Carbon) oC Silicon Carbide (SiC) 2700 oC Boron Nitride (BN) oC
Covalent bonds are also very strong!

26. HOWEVER LOOK AT THESE MELTING POINTS…
CH oC
O oC
F oC
How come they are so low??

27. Third type of chemical bonding…
“Van der waals Forces”
The sum of the attractive or repulsive forces between molecules
other than those due to covalent bonds or the electrostatic interaction of ions with one another.

28. Third type of chemical bonding…
“Van der waals Forces”
INTRAmolecular INTERmolecular
(within/inside the molecule) (between)
COVALENT BONDS Van Der Waals

29. The covalent intramolecular bond in I2 is very strong.
There are weaker intermolecular forces which hold covalent molecules together in a molecular solid. I I I I

30. Intra Vs Inter molecular forces

31. 2 types of Van der Waals London forces Dipole-dipole forces
London Forces are weak attractive forces which exist between atoms as a result of temporary dipoles
Dipole-dipole forces
A permanent dipole
So what are dipoles??????

32. What are dipoles?
Dipole –

33. Polarization causes dipoles!

34. LONDON FORCES
London Forces –

35. London Forces London Forces: The WEAKEST TYPE of bonding force
ALWAYS present, even in species which have covalent or ionic bonding
IMPORTANT??? when they are the only force of attraction....
adjacent noble gas atoms
adjacent covalently-bonded molecules
The greater the atomic number, the stronger the London forces it experiences

36. homework
P172 #57
P173 #59,60
P 175 #62,63,64
P177 #68, 69
P 179 #72 from a to k
P 181 #74,76,78
Read summary on page 182 and try to solve the summary exercises if you have time.