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Dr Nurul Huda Abd Karim 2013

STKK2313Kimia Kumpulan Utama dan Peralihan

(Main Group and Transition Element Chemistry)

Introduction

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Classification of Elements

Main group elements - representative

elements Group 1A-7A - Group 8A all have ns2np6

configuration (exception-He)

Transition elements - 1B, 3B - 8B d-block

Lanthanides/actinides - f-block

The Modern Periodic Table

(revision)

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http://library.thinkquest.org/2690/ptable/ptable.html

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Ionization energy (IE): minimum energy neededto remove an electron from an atom in the gasphase

Representation:

Na(g) Na+

(g) + e

IE for this 1st ionization = 495.8 kJ/mol

In general, ionization energy as Zeff

Exceptions occur due to the stability of specificelectron configurations

Ionization energy

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IE1 (kJ/mol) Values for Main Group Elements

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IE1 Trend

High value of IE1

associated to noble

gases

very low IE1 for G1

IE1 increase across a

given period

similar IE1 for d-block

MBKassim 2006/07 8

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What do you notice about the 1st IE across a

period? Why? (hint: Zeff)

What do you notice about the 1st IE down a

column? Why? (hint: n)

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Explain

What do you notice about the 1st IE between 2Aand 3A? Why? (hint: draw the electronconfiguration)

What do you notice about the 1st IE between 5Aand 6A? Why? (hint: draw the electronconfiguration)

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Multiple Ionizations: it takes more energy to

remove the 2nd, 3rd, 4th, etc. electron and much

more energy to remove core electrons Why?

Core electrons are closer to nucleus

Core electrons experience greater Zeff

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Copyright McGraw-Hill 2009

Electron Affinity (EA): energy released when an

atom in the gas phase an electron

Representation:Cl(g) + e

Cl(g)

EA for this equation 349.0 kJ/mol energy

released (H = negative)

Electron Affinity

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Copyright McGraw-Hill 2009

EA (kJ/mol) Values for Main Group Elements

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Copyright McGraw-Hill 2009

14

Periodic Trends in EA

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Electronegativity Trend

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Electronegativity

Established by Linus Pauling (1930s)

the tendency of an atom in a molecule to attract electrons toitself

If an atom of an element has strong tendency to aquire

electrons, Highly Electronegative

(Pauling) = the difference between bond dissociationenthalpy and enthalpy change of atomization diatomic X2 ingas phase

Usage of electronegativity values : 1) deciding bond

polarities 2) estimating the importance of possibleresonance structures for molecules Example; HCl - hydrogen at the positive end of the

dipole, chlorine at the negative end

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Periodic Trends in Chemical

Properties of Main Group Elements

IE, EA and electronegaticity enable us to

understand types of reactions that elements

undergo and the types of compounds formed