Transcript Document

Final Note on Nodes
• The H atom wave functions tell us that there
are only radial nodes for the 1s, 2s, 3s..
orbitals. Angular or planar nodes become
important as we move to p orbitals (one planar
node) and d orbitals (2 planar nodes). This is
seen in the slide on the next table and
graphical representations of d orbitals. (Orbital
shapes impt in chemical bonding.)
Hydrogen Atom Wavefunctions –
Number of Nodes
Orbital
Designation
Total # Nodes
(n-1)
Planar Nodes
(l)
Radial Nodes
1s
0
0 (s orbital)
0
2s
1
0 (s orbital)
1
2p
1
1 (p orbital)
0
3s
2
0 (s orbital)
2
3p
2
1 (p orbital)
1
3d
2
2 (d orbital)
0
FIGURE 8-30
Representations of the five d orbitals
Copyright © 2011 Pearson
Canada Inc.
General Chemistry: Chapter 8
Slide 3 of 50
The Periodic Table
• In studying the electronic structure of atoms
we mentioned that chemical families of
elements have similar valence shell electron
configurations. Historically, however, a
detailed knowledge of atomic structure came
subsequent to the observation that groups of
elements had similar chemical properties.
The Periodic Table
• In the modern Periodic Table elements are
arranged in order of increasing atomic number
so that groups of elements with similar
chemical properties appear in columns. The
100+ known elements are commonly divided
into three groups – the metals, non-metals and
the metalloids. These three sets of elements
have rather different physical properties.
Metals and Nonmetals and Their Ions
• Metals
– Good conductors of heat and electricity.
– Malleable and ductile.
– Moderate to high melting points.
• Nonmetals
– Nonconductors of heat and electricity.
– Brittle solids.
– Some are gases at room temperature.
• Metalloids
– Metallic and non-metallic properties
Slide 6 of
35 Pearson
Copyright
© 2011
Canada Inc.
General Chemistry: Chapter 9
Slide 6 of 35
Electrical and Thermal Conductivity
• The next two slides present electrical and
thermal conductivity data (room temperature)
for a number of elements. The periodic trends
are more important than the units. For
illustrative purposes relative thermal
conductivities are shown on the second slide.
Again, in the modern world, silicon is rather
important!
•
Electrical Conductivity Elements
Element
Conductivity
(S/m)
Cost ($/kg)
Element Type
Silver
6.2 x 107
1,198
Metal
Copper
5.9 x 107
8.1
Metal
Gold
4.5 x 107
62,000
Metal
Nickel
1.4 x 107
Iron
1.0 x 107
Inexpensive
Metal
Germanium
2.0 x 103
Expensive
Metalloid
Silicon
1.0 x 103
Variable
Metalloid
Bromine
1.0 x 10-10
Sulfur
1.0 x 10-15
Metal
Nonmetal
Inexpensive
Nonmetal
http://periodictable.com/Properties/A/ElectricalConductivity.v.html
Thermal Conductivity Elements
Element
Relative Thermal
Conductivity
Element Type
Silver
1.000
Metal
Copper
0.93
Metal
Gold
0.74
Metal
Nickel
0.21
Metal
Iron
0.19
Metal
Germanium
0.14 (Suprise?)
Metalloid
Silicon
0.35(Surprise?)
Metalloid
Bromine
0.00028
Nonmetal
Sulfur
0.00048
Nonmetal
http://periodictable.com/Properties/A/ThermalConductivity.v.html
The Periodic Table
• Much early work on the Periodic Table was
done by the Russian chemist Dimitri
Mendeleev and the German chemist Lothar
Meyer. (The English chemist John Newlands
noticed that elements, when ordered according
increasing atomic weight showed
“recurring/similar” chemical and physical
properties at intervals of eight elements.) It
goes without saying that all famous chemists
eventually receive philatelic recognition.
9-1 Classifying the Elements: The
Periodic Law and the Periodic Table
•1869
Dimitri Mendeleev
Lothar Meyer
When the elements are arranged in order
of increasing atomic mass, certain sets of
properties recur periodically.
Slide 11©of2011
35 Pearson
Copyright
Canada Inc.
General Chemistry: Chapter 9
Slide 11 of 35
Periodic Table - Many Subdivisions!
• The Periodic Table may be subdivided in many
ways. One finds metals on the left and nonmetals on the right. Elements with similar
chemical properties appear in columns. As one
moves across a row or period in the Periodic
Table a range of chemical and physical
properties is seen. Periods generally end with a
chemically unreactive Noble Gas ( a Noble
Gas compound was first synthesized in
Canada).
Periodic Table - Many Subdivisions!
• Further subdivisions of the Periodic Table are
illustrated on the next slide. One can , for
example, divide the elements into Main Group
elements and Transition Metals. From high
school chemistry you will recall that transition
metals have relatively complex chemistry –
forming, for example, a variety of ions in ionic
compounds (eg. Fe2+ and Fe3+).
Metal and Non-metal Monatomic Ions
• Another familiar result/fact from high school
chemistry is that in ionic compounds metals
form a range of positive ions and non-metals
from negative ions. Main Group metals
typically lose one or more electrons to form a
monatomic ion with a Noble Gas electron
configuration. Main Group non-metals gain
one or more electrons and also form
monatomic ions with a Noble Gas electron
configuration.
Main-Group Metal Ions
Metals tend to lose electrons to attain noble gas electron
configurations.
Slide 15©of2011
35 Pearson
Copyright
Canada Inc.
General Chemistry: Chapter 9
Slide 15 of 35
Main-Group Nonmetal Ions
Nonmetals tend to gain electrons to attain noble-gas
electron configurations
Slide 16©of2011
35 Pearson
Copyright
Canada Inc.
General Chemistry: Chapter 9
Slide 16 of 35
Slide 17©of2011
35 Pearson
Copyright
Canada Inc.
General Chemistry: Chapter 9
Slide 17 of 35
Atomic and Ionic Radii
• The “size” of an individual H atom or He atom
(for example) in the gas phase in difficult to
define exactly. Why? (Recall the probabilistic
description of electronic structure considered
earlier and in Chapter 8 of the text).For
molecules we can use spectroscopic methods
to determine internuclear distances in gas
phase molecules. X-ray diffraction gives
internuclear distances in crystalline solids.
Atomic and Ionic Radii
• We will use spectroscopic and X-ray
diffraction data to give us working estimates of
atom and ionic radii (sizes). Atoms are small.
We will use picometers (pm = 10-12m) and
Angstroms (10-10 m) to describe atom/ion
sizes. From a homonuclear diatomic molecule
(such as H2, Cl2 or Na2) the covalent radius of
an atom can be obtained as half of the
internuclear separation.
9-3 Sizes of Atoms and Ions
FIGURE 9-3
•Covalent, metallic, and ionic radii compared
Slide 20©of2011
35 Pearson
Copyright
Canada Inc.
General Chemistry: Chapter 9
Slide 20 of 35
Atomic and Ionic Radii - Surprises?
• The results presented on the previous slide are
perhaps a little startling. Let’s use the metallic
radius for Na as an estimate for the size of a
neutral Na atom.
•
Na → Na+ + e(11e-)
(10e-)
• Both the Na atom and the Na+ ion have 11
protons. If removing an e- from an atom were a
process analogous to peeling an orange we might
expect the Na atom to be about 10% larger than
the Na+ ion.
7/28/2015Copyright © 2011
Pearson Canada Inc.
General Chemistry: Chapter 9
Slide 21 of 35
Atomic and Ionic Radii - Surprises?
• In fact, the Na atom (radius ~ 186 pm) and the
Na+ ion (radius ~ 99 pm) have very different
sizes. On a volume basis the relative sizes are
given by (186pm/99pm)3 = 6.6! We can gain
some insight into this large difference by
looking first at the electron configurations of
the Na atom and the Na+ ion.
• Na atom: 1s22s22p63s1
• Na+ ion: 1s22s22p6
7/28/2015Copyright © 2011
Pearson Canada Inc.
General Chemistry: Chapter 9
Slide 22 of 35
Atomic and Ionic Radii - Continued
• We see that the Na atom has electrons in two
principal energy levels but the Na+ ion has
only two principal energy levels with
electrons. Moving from the Na atom to the Na+
ion the number of (repulsive) coulombic
interactions between electrons also drops.
Why? This effect should also cause the size of
the ion to be smaller than that of the neutral
atom.
Atomic and Ionic Radii - Continued
• A concept of screening electrons and effective
nuclear charge is very useful in discussing atomic
radii, ionization energies and other properties
that show periodic trends. The key idea is that
the outermost electrons in an atom experience
an effective nuclear charge that is smaller than
the actual nuclear charge due to the presence of
the “inner” or screening electrons that lie closer
(on average!) to the nucleus than the valence
electrons.
Atomic and Ionic Radii - Continued
• The concepts of screening electrons and
effective nuclear charge are illustrated on the
next slide for the magnesium (Mg) atom. The
atomic number of Mg is 12 (12 protons). The
condensed electron configuration for the Mg
atom is 1s22s22p63s2. The number of core or
inner electrons lying “between” the valence
electrons and the nucleus is 10. We say that the
valence electrons see an effective nuclear
charge of +2. Zeffective = Z – S = 12 -10 = 2
Screen of electron charge
from 10 core electrons
(12+)
(-)
(-)
FIGURE 9-6
The shielding effect and effective nuclear charge, Zeff
Slide 26©of2011
35 Pearson
Copyright
Canada Inc.
General Chemistry: Chapter 9
Slide 26 of 35
Ionic Radius
FIGURE 9-7
•A comparison of atomic and ionic sizes
Slide 27©of2011
35 Pearson
Copyright
Canada Inc.
General Chemistry: Chapter 9
Slide 27 of 35
Ionic Radius
Cations are smaller than the atoms from which they are
formed.
For isoelectronic cations, the more positive the ionic
charge, the smaller
the ionic radius.
Anions are larger than the atoms from which they are
formed. For isoelectronic anions, the more negative the
charge, the larger the ionic radius.
Slide 28©of2011
35 Pearson
Copyright
Canada Inc.
General Chemistry: Chapter 9
Slide 28 of 35
FIGURE 9-8
Covalent and anionic radii compared
Slide 29©of2011
35 Pearson
Copyright
Canada Inc.
General Chemistry: Chapter 9
Slide 29 of 35
FIGURE 9-9
A comparison of some atomic and ionic radii
Slide 30©of2011
35 Pearson
Copyright
Canada Inc.
General Chemistry: Chapter 9
Slide 30 of 35
Sodium Atom and Sodium Ion
• The startling contraction in size when the
sodium ion forms from the neutral atom
reflects the fact that the third principal energy
level has been emptied completely, the
outermost electrons are now more strongly
attracted to the nucleus and electron-electron
repulsions have been reduced. Why?
Periodic Table – Binary Ionic
Compounds
• Class Examples: We’ll look at several
examples of writing chemical reactions for
binary ionic (metal-nonmetal) compounds
from the constituent elements. As well, we
want now to be able to recognize basic oxides
and consider their reactions with water. We’ll
look at the more comples examples of binary
covalent compounds in a few days.