6 – Electronegativity

6 ElectronegativityLeaving Certificate Chemistry

By the end of todays class you should be able to :Define electronegativityTell what the trend is as you go across a groupTell what the trend is as you go down a groupBe able to explain these trends

Electronegativity2008 Q5 (a) (5)2006 Q5 (a) (6)2005 Q5 (a) (6)2003 Q5 (a) (6)

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The electronegativity of an element is a measureof the power of attraction of an atom of that elementfor the shared pair of electrons in a covalent bond.

Definition

Electronegativity Table (Page 46 MT)

H2.1He----Li1.0Be1.5B2.0C2.5N3.0O3.5F4.0Ne----Na0.9Mg1.2Al1.5Si1.8P2.1S2.5Cl3.0Ar----K0.8Ca1.0Ga1.6Ge1.8As2.0Se2.4Br2.8Kr----

Learning objectivesWhat the trend going across any period in the Periodic table is and an explanation of thisWhat the trend going down any group in the table is and an explanation of this

Lithium3456What happens to the nuclear charge? What happens to the number of shells filled?BeryliumBoronCarbonWhat happens to the size of the atom?

Values Increase across any PeriodLithiumBerylliumBoronCarbonNitrogen1. Nuclear charge is increasing2. Atomic radii are decreasing2006 Q5 (b) (6)

31119What happens to the size of the nuclear charge?What happens to the number of shells filled?What happens to the size of the atom (atomic radius)?

Values decrease down any GroupLithiumSodiumPotassiumIncreasing Nuclear charge BUT the effect (on the outermost electron) is offset by an inner electron screening effect2. Atomic Radii are increasing as you go down any group2008 Q5 (b) (9)1119

Learning objectivesKnow the rules for predicting bonding type between atomsBe able to use these rules to correctly predict bonding type used.

Predicting the bond typeElectronegativity Values can be used to predict the bond type of molecules in a chemical bondWith 2 Bonding AtomsDifference in electronegativity0Bond is Non-polar (pure Covalent)Between 0.4 - 1.7Bond is Polar (Covalent)Greater than 1.7Bond is Ionic2008 Q5 (c) (9)2007 Q5 (b) (6)Between 0 - 0.4Bond is weakly polar(Covalent)

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

Use electronegativity values to predict the type of bonding in waterOxygen (EV) = 3.5 Water is a polar (Covalent) moleculeHydrogen (EV) = 2.1 Difference in EV = 1.4

Use electronegativity values to predict the type of bonding in methaneCarbon (EV) = 2.5 Methane is a slightly weakly polar (Covalent) moleculeHydrogen (EV) = 2.1 Difference in EV = 0.4

Use electronegativity values to predict the type of bonding in magnesium chlorideMagnesium (EV) = 1.2 Magnesium chloride is an ionic moleculeChlorine (EV) = 3.0 Difference in EV = 1.8MgCl21MgCl2

Use electronegativity values to predict the type of bonding in hydrogen sulfideHydrogen EV) = 2.1 Sulfur (EV) = 2.5 Difference in EV = 0.4HS12H2SHydrogen sulfide is a slightly weakly polar (Covalent) molecule

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