Leaving Certificate Chemistry 6 – Electronegativity Leaving Certificate Chemistry
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
Electronegativity 2008 Q5 (a) (5) 2006 Q5 (a) (6) 2005 Q5 (a) (6) 2003
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
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
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?
Values Increase across any Period Lithium Beryllium Boron Carbon Nitrogen 1. Nuclear charge is increasing 2. Atomic radii are decreasing 2006 Q5 (b) (6)
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
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)
Learning objectives Know the rules for predicting bonding type between atoms Be able to use these rules to correctly predict bonding type used.
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 0.4 - 1.7 Between 0 - 0.4 Bond is weakly polar Bond is Ionic Bond is Polar (Covalent) (Covalent)
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
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
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
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
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