1. Leaving Certificate Chemistry
6 – Electronegativity
Leaving Certificate Chemistry

2. By the end of today’s class you should be able to :
Define electronegativity
Tell what the trend is as you go across a group
Tell what the trend is as you go down a group
Be able to explain these trends

3. Electronegativity 2008 Q5 (a) (5) 2006 Q5 (a) (6) 2005 Q5 (a) (6) 2003

4. Electronegativity Table (Page 46 – MT)H
2.1 He
---- Li
1.0 Be
1.5 B
2.0 C
2.5 N
3.0 O
3.5 F
4.0 Ne Na
0.9 Mg
1.2 Al Si
1.8 P S Cl Ar K
0.8 Ca Ga
1.6 Ge As Se
2.4 Br
2.8 Kr

5. Learning objectives
What the trend going across any period in the Periodic table is and an explanation of this
What the trend going down any group in the table is and an explanation of this

6. What happens to the number of shells filled?
Going across period 1
Lithium
Berylium
Boron
Carbon 3 4 6 5
What happens to the number of shells filled?
What happens to the nuclear charge?
What happens to the size of the atom?

7. Values Increase across any Period
Lithium
Beryllium
Boron
Carbon
Nitrogen
1. Nuclear charge is increasing
2. Atomic radii are decreasing
2006
Q5 (b) (6)

8. What happens to the size of the atom (atomic radius)? 3
Going down group 1
What happens to the size of the atom (atomic radius)?
What happens to the number of shells filled?
What happens to the size of the nuclear charge? 11 19

9. Values decrease down any Group
Increasing Nuclear charge BUT the effect (on the outermost electron) is offset by an inner electron screening effect
Lithium 11
Sodium
2. Atomic Radii are increasing as you go down any group
Potassium 19
2008
Q5 (b) (9)

10. Learning objectives
Know the rules for predicting bonding type between atoms
Be able to use these rules to correctly predict bonding type used.

11. Predicting the bond type
Electronegativity Values can be used to predict the bond type of molecules in a chemical bond
With 2 Bonding Atoms
2008
Q5 (c) (9)
Difference in electronegativity
2007
Q5 (b) (6)
Bond is Non-polar (pure Covalent)
Greater
than 1.7
Between
Between
Bond is weakly polar
Bond is Ionic
Bond is Polar (Covalent)
(Covalent)

12. Iodine is a non-polar (Covalent) molecule
Use electronegativity values to predict the type of bonding in iodine (I2)
iodine (EV) = 2.7
Iodine (EV) = 2.7
Difference in EV = 0
Iodine is a non-polar (Covalent) molecule

13. Use electronegativity values to predict the type of bonding in water
Oxygen (EV) = 3.5
Hydrogen (EV) = 2.1
Difference in EV = 1.4
Water is a polar (Covalent) molecule

15. Use electronegativity values to predict the type of bonding in methane
Carbon (EV) = 2.5
Hydrogen (EV) = 2.1
Difference in EV = 0.4
Methane is a slightly weakly polar (Covalent) molecule

16. Magnesium chloride is an ionic molecule
Use electronegativity values to predict the type of bonding in magnesium chloride
Magnesium (EV) = 1.2
Chlorine (EV) = 3.0
Difference in EV = 1.8 Mg Cl
Magnesium chloride is an ionic molecule 2 1
MgCl2

17. Hydrogen sulfide is a slightly weakly polar (Covalent) molecule
Use electronegativity values to predict the type of bonding in hydrogen sulfide
Hydrogen EV) = 2.1
Sulfur (EV) = 2.5
Difference in EV = 0.4 H S
Hydrogen sulfide is a slightly weakly polar (Covalent) molecule 1 2
H2S