Download iClicker Participation Question

2/25/2014
“An expert is a person who has made all the mistakes that can be
made in a very narrow field.”
—Niels Bohr
“The only real mistake is the one from which we learn nothing.”
— John Powell

Today:

◦ Periodic Properties:
 Electron Shielding & Effective
Nuclear Charge
 Atomic Radii
 Ionic Radii
 Ionization Energy
 Electron Affinity
◦ Electron Configurations & the
OCTECT Rule
Midterm EXAM 1:
◦ Scores posted to gradebook
on canvas
◦ Please see me if your score is
< 70 %

Next Monday:
◦ Read Chp. 3, Sections 3.93.14, pp. 118-129
iClicker Participation Question:
Review of VALENCE Electrons vs. CORE electrons
Write the electron configuration for the VALENCE electrons of
a neutral Selenium atom.
A. 1s22s22p63s23p64s23d104p4
B. 1s22s22p63s23p6
C. 4s23d104p4
D. 4s24p4
Valence Electrons: e- in outer
most s & p orbitals.
•
•
If the d orbitals are fully filled,
they become CORE electrons
If the d orbitals are only
PARTIALLY filled, they are still
considered valence electrons
E. 4p4
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Core Electrons & Valence Electrons:
fully filled
shells of electrons buried
deep within the atom.
Electrons in
the outmost shell on the surface
of the atom. These are the
electrons involved in bonding
and chemical reactions.
Summary of Quantum Mechanics:

Electrons exist in orbitals around nuclei as MATTER WAVES:
◦ The orbitals are filled in layers or SHELLS with different shapes
& energies

Electrons PAIR UP in atomic orbitals…

The INNER SHELLS are composed of CORE ELECTRONS. These do
not participate in chemical reactions.

The OUTER SHELL is composed of VALENCE ELECTRONS. These
are more exposed & participate in chemical reactions.
◦ The number of valence electrons corresponds to the group
number (i.e. 1A for Na, 2A for Mg, etc.)
Pure Substances
Elements:
Compounds:
Only one type of atom
combinations of elements
Molecular: Molecular:
Atomic:
Single atoms
Ionic:
Atoms of multiple
Atoms of only one
Atoms of multiple
element connected elements connected elements locked into
into a molecule
into a molecule
a periodic lattice
GOAL: Understand how complex substances
behave based on their basic ELECTRONIC & ATOMIC
STRUCTURE.
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Atomic Radius (Size):
The size of an atom is determined by the
electron orbitals

The atomic radius of an element can be
defined as half the distance between the
nuclei of a diatomic molecule of the
element.

For example: the atomic radius of carbon
is 77 picometers (7.7 x 10-11 m).
Radius determination for a metal atom (Al)
Nanoparticles visualized with Transmission
Electron Microscope (TEM)
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ATOMIC RADIUS (pm)
We might expect the atomic radii of elements to increase
as we move from LEFT to RIGHT across the periodic table.
However, experimentally, this is not observed. Why not?
ATOMIC NUMBER (Z)
Increasing Effective Nuclear Charge (Zeff)
Effective nuclear charge (Zeff) and Shielding
 Zeffective is
the average shielded charge
felt by an electron.
in an atom is the “blocking”
or canceling of positive charge by core
electrons.
 Shielding
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we move from left  right on the periodic table,
shielding of the nucleus by inner (core) electrons remains
constant. (Shielding by other outer electrons is minimal.)
 As
 However,
as the number of protons increases, the
electrons in the valence (outer) shell experience a greater
attraction for the nucleus – a higher Zeffective.
 Because
of the
greater pull on the
outer electrons as we
move across the
periodic table, atomic
radius generally
DECREASES from
left right within a
period.
Atomic Radii
(pm)
As we move from top
 bottom on the
periodic table, we
would expect the
atomic radius to
INCREASE, and it does,
because the energy
level of the outer e-’s
increases:
1s→2s→3s→4s→etc.
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iClicker Participation Question:
Trends in Atomic Size
Rank the atoms below from smallest to largest atomic radius.
A. Cl < F < S < Ba
B. F < Cl < S < Ba
C. Ba < S < Cl < F
D. F < Cl < Ba < S
E. None of the above are correct
Periodic Properties in the Periodic Table:
The chemical properties of elements
are largely determined by
The Noble gases all have 8 valence electrons FULLY FILLING
the outermost shell. This is called an OCTET.
Elements will react to lose or gain enough
electrons to arrive at a Noble gas electron
configuration with a complete OCTET.
The Alkali metals all have 1 valence electron in their neutral form
Chemical Reactions based on Electron Configurations:
Elements will react to lose or gain enough
electrons to arrive at a Noble gas electron
configuration with a complete OCTET.
Metals LOSE
electrons to reach a
complete OCTET
with a Noble gas
configuration.
Nonmetals GAIN
electrons to reach a
complete OCTET
with a Noble gas
configuration.
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Ionization Energy
First Ionization Energy – the energy required to remove
the highest energy electron from an isolated atom in the
gaseous state.

Second Ionization Energy – the energy required to
remove the second highest energy electron from the +1
ion.

Third, Fourth, Fifth, etc.

Ionization energies are positive: they refer to the energy
ABSORBED by the atom (system) to remove an electron.
A negative energy indicates energy is RELEASED.
1st Ionization Energy

Why does oxygen have an
anomalously low ionization energy?
Or sulfur for that matter?
ATOMIC NUMBER (Z)

LR trend: 1st ionization energy INCREASES, because the pull on
the outermost electron increases: Zeff increases.

TB trend: 1st ionization energy DECREASES, because the
outermost electron is at a higher energy level.
2nd Ionization Energy and higher…
Beryllium 1st ionization:
Beryllium
2nd
ionization:
Beryllium 3rd ionization:
Be (1s22s2) → Be+ (1s22s1 ) + 1eBe+ (1s22s1) → Be2+ (1s2) + 1eBe2+ (1s2) → Be2+ (1s1) + 1e-
A LARGE JUMP between subsequent ionization energies is
observed when core electrons start to be removed.
(in kJ/mol)
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Ionic Radii
Reported Ionic radii are
determined from the
measured distances
between nuclei in ionic
compounds.

Cations are always smaller than the atom they are
derived from. In many cases, the outer energy level of
the cation is one energy level lower than that of the
atom.

Anions are always larger than the atom they are derived
from, primarily due to repulsive forces of electrons in the
outer energy level.
Size Change in Ion Formation
Size Change in Ion Formation
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ANIONS
CATIONS
Ionic Radii (pm)

The LR trend for ionic radius is DECREASING for the same type
of ion – cation or anion.

The TB trend is INCREASING.
iClicker Participation Question:
Trends in the Size of IONS
Rank the ions below from smallest to largest IONIC radius.
A. S2- < Cl- < Na+ < Mg2+
B. Cl- < S2- < Mg2+ < Na+
C. Na+ < Mg2+ < S2- < ClD. Mg2+ < Na+ < Cl- < S2E. None of the above are correct
Electron Affinity

The energy absorbed (+) or released (-) when an
isolated gaseous atom ACCEPTS an electron to become
a negative ion.

LR trend: Generally increasing, because the
attraction for the outermost electrons increases from
left to right.

TB trend: Generally decreasing, but trend is not
highly predictable from top to bottom.
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Table of Electron Affinities
• Why does Nitrogen have an anomalously low
electron affinity?
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