CHEM1112 Lecture Notes - Lecture 17: Ionization Energy, Diagonal Relationship, Atomic Orbital

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Recognise trends in the periodic table and the
correlation between the trends in atomic radii,
ionisation energies and electronegativity
Explain the origin of these trends in terms of the
electronic structure of the atoms
4.8-9
Atomic
radii
Decrease across a period and UP a group
-
Increase in nuclear charge Z
Increase in e-/e- repulsion
-
Electrons added DO NOT SHIELF the
increasing nuclear charge effectively
Increase in effective nuclear charge Zeff
So moving across period orbitals
become smaller (ie. Size
decreases) -> lower energy
Larger Zeff exerts stronger electrostatic
attraction on the electron cloud ->
smaller orbitals
Zeff increases across a period
Electrons move VERY fast and can avoid each
other
-
Increase in principal quantum number n
Increase in shell size
Electrons in inner shells shield charge,
cancels effect of additional protons in
nucleus
Increase in size down each group
-
Screen clipping taken: 28/10/2017 5:51 PM
Diagonally related elements often have similar
properties (diagonal relationship)
Ionic
radii
Zeff increases
Cations are smaller than the respective
atom
Ions decrease with size of positive charge
Ionisation decreases e-/e- repulsion
-
Zeff decreases
Anions are larger than the respective
atom
Ions increase with size of negative charge
Adding an electron increases e-/e- repulsion
-
Anions often much larger than cations
-
Decrease across period
Increase down each group
For ions of same charge
-
Ionisati
Minimum amount of energy needed to remove
-
17.1, 17.2
Saturday, 28 October 2017
4:44 PM
17. Periodic trends Page 1
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Ionisati
on
energie
s
Minimum amount of energy needed to remove
an electron from a neutral atom is the FIRST
ionisation energy
-
Smaller atoms = higher ionisation energies
-
Screen clipping taken: 28/10/2017 6:13 PM
Electro
negativi
ty
Increases with Zeff
Decreases with atomic size
Tendency of an atom to attract electrons
towards itself in a molecule
-
Screen clipping taken: 28/10/2017 6:14 PM
17. Periodic trends Page 2
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Document Summary

Recognise trends in the periodic table and the correlation between the trends in atomic radii, ionisation energies and electronegativity. Explain the origin of these trends in terms of the electronic structure of the atoms. Decrease across a period and up a group. Electrons move very fast and can avoid each other. Electrons added do not shielf the increasing nuclear charge effectively. Larger zeff exerts stronger electrostatic attraction on the electron cloud -> smaller orbitals. So moving across period orbitals become smaller (ie. size decreases) -> lower energy. Diagonally related elements often have similar properties (diagonal relationship) Electrons in inner shells shield charge, cancels effect of additional protons in nucleus. Ionisati minimum amount of energy needed to remove: periodic trends page 1. Minimum amount of energy needed to remove an electron from a neutral atom is the first ionisation energy. Tendency of an atom to attract electrons towards itself in a molecule.

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