Transcript Chapter 7 Periodic Properties of the Elements

Chapter 7
Periodic Properties
of the Elements
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Development of Periodic Table
Dmitri
Mendeleev and
Lothar Meyer
independently
came to the
same conclusion
about how
elements should
be grouped.
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Periodic
Properties
of the
Elements
Development of the Periodic Table
Mendeleev, for instance, predicted the discovery of
germanium (which he called eka-silicon) as an element
with an atomic weight between that of zinc and arsenic,
but with chemical properties similar to those of silicon. Periodic
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Properties
of the
Elements
A.
B.
C.
D.
Lanthanides because some of the elements are not stable
Row 6, missing atomic numbers of elements between Ba and Lu
Row 6, Rn is the start of elements that are radioactive
Periodic
Properties
Row 7, elements in this row are generally radioactive
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of the
Elements
A.
B.
C.
D.
Atomic weight has uncertainty in measurement, whereas
atomic number depends only on number of protons.
Atomic weight depends both on number of protons and
neutrons.
Atomic weight is greatly influenced by number of electrons,
not protons.
Atomic weight depends both on number of protons and
electrons.
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Periodic
Properties
of the
Elements
A.
B.
C.
D.
Co/Ni
Th/Pa
Te/I
All of the above
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Periodic
Properties
of the
Elements
Periodic Trends
• In this chapter, we will rationalize observed
trends in
– Sizes of atoms and ions.
– Ionization energy.
– Electron affinity.
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Periodic
Properties
of the
Elements
Effective Nuclear Charge
• In a many-electron atom,
electrons are both attracted to
the nucleus and repelled by
other electrons.
• The nuclear charge that an
electron experiences depends on
both factors.
The effective nuclear charge, Zeff, is
found this way:
Zeff = Z − S
where Z is the atomic number
and S is a screening constant,
usually close to the number of
inner electrons.
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Periodic
Properties
of the
Elements
A. 2s
B. 2p
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Periodic
Properties
of the
Elements
A.
B.
C.
D.
2p electron of a Ne atom
3s electron of a Na atom
Both experience the same effective nuclear charge
Requires a table of shielding constants to make an
estimation
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Periodic
Properties
of the
Elements
What Is the Size of an Atom?
The bonding
atomic radius is
defined as one-half
of the distance
between covalently
bonded nuclei.
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Periodic
Properties
of the
Elements
Sizes of Atoms
The bonding atomic
radius tends to
— Decrease from left to
right across a row
(due to increasing Zeff).
— Increase from top to
bottom of a column
(due to the increasing
value of n).
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Periodic
Properties
of the
Elements
A.
B.
C.
D.
Bottom and left
Bottom and right
Top and left
Top and right
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Periodic
Properties
of the
Elements
Sample Exercise 7.1 Bond Lengths in a Molecule
Natural gas used in home heating and cooking is odorless. Because natural gas leaks pose the danger of
explosion or suffocation, various smelly substances are added to the gas to allow detection of a leak. One
such substance is methyl mercaptan, CH3SH. Use Figure 7.6 to predict the lengths of the C—S, C—H,
and S—H bonds in this molecule.
FIGURE 7.6 Trends in bonding atomic radii for
periods 1 through 5.
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Periodic
Properties
of the
Elements
A.
B.
C.
D.
Trends work with each other but trend in orbital size is more
important.
Trends work with each other but trend in effective nuclear
charge is more important.
Trends work against each other but trend in orbital size is
more important.
Trends work against each other but trend in effective nuclear
charge is more important.
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Periodic
Properties
of the
Elements
Sample Exercise 7.2 Atomic Radii
Referring to a periodic table, arrange (as much as possible) the atoms 15P, 16S, 33As, and 34Se in order of
increasing size. (Atomic numbers are given to help you locate the atoms quickly in the table.)
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Periodic
Properties
of the
Elements
Sizes of Ions
•
•
•
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Ionic size depends upon
– The nuclear charge.
– The number of electrons.
– The orbitals in which
electrons reside.
Cations are smaller than
their parent atoms:
– The outermost electron is
removed and repulsions
between electrons are
reduced.
Anions are larger than their
parent atoms”
– Electrons are added and
repulsions between
electrons are increased.
Periodic
Properties
of the
Elements
Sizes of Ions
• Ions increase in size
as you go down a
column:
– This increase in size
is due to the
increasing value of n.
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Periodic
Properties
of the
Elements
Sizes of Ions
• In an isoelectronic series, ions have the
same number of electrons.
• Ionic size decreases with an increasing
nuclear charge.
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Periodic
Properties
of the
Elements
A.
B.
C.
D.
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Minimal change
Larger
Smaller
Trend varies by column
Periodic
Properties
of the
Elements
Sample Exercise 7.3 Atomic and Ionic Radii
Arrange Mg2+, Ca2+, and Ca in order of decreasing radius..
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Periodic
Properties
of the
Elements
Sample Exercise 7.4 Ionic Radii in an Isoelectronic Series
Arrange the ions K+, Cl–, Ca2+, and S2– in order of decreasing size.
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Periodic
Properties
of the
Elements
Ionization Energy
• The ionization energy is the amount of
energy required to remove an electron
from the ground state of a gaseous
atom or ion.
– The first ionization energy is that energy
required to remove the first electron.
– The second ionization energy is that
energy required to remove the second
electron, etc.
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Periodic
Properties
of the
Elements
A.
B.
C.
D.
First ionization step, because it takes more energy and
hence shorter wavelength.
First ionization step, because it takes less energy and hence
shorter wavelength.
Second ionization step, because it takes more energy and
hence shorter wavelength.
Periodic
Second ionization step, because it takes less energy andProperties
hence shorter wavelength.
of the
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Elements
Ionization Energy
• It requires more energy to remove each
successive electron.
• When all valence electrons have been removed,
the ionization energy takes a quantum leap.
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Periodic
Properties
of the
Elements
A.
B.
C.
I1 for the boron atom is equal to I2 for the carbon atom.
I2 for the carbon atom is greater.
I1 for the boron atom is greater.
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Periodic
Properties
of the
Elements
Sample Exercise 7.5 Trends in Ionization Energy
Three elements are indicated in the periodic table in the margin. Which one has the largest second
ionization energy?
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Periodic
Properties
of the
Elements
Trends in First Ionization Energies
• As one goes down a
column, less energy
is required to remove
the first electron.
– For atoms in the same
group, Zeff is
essentially the same,
but the valence
electrons are farther
from the nucleus.
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Periodic
Properties
of the
Elements
Trends in First Ionization Energies
• Generally, as one goes
across a row, it gets harder
to remove an electron.
– As you go from left to
right, Zeff increases.
• However, there are two
apparent discontinuities in
this trend.
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Periodic
Properties
of the
Elements
Trends in First Ionization Energies
• The first occurs between
Groups IIA and IIIA.
• In this case the electron is
removed from a p orbital
rather than an s orbital.
– The electron removed is
farther from the nucleus.
– There is also a small amount
of repulsion by the s
electrons.
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Periodic
Properties
of the
Elements
Trends in First Ionization Energies
• The second
discontinuity occurs
between Groups VA
and VIA.
– The electron removed
comes from a doubly
occupied orbital.
– Repulsion from the
other electron in the
orbital aids in its
removal.
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Periodic
Properties
of the
Elements
A.
B.
C.
D.
As; outer electrons experience larger Zeff than those in Ar.
As; outer electrons experience smaller Zeff than those in Ar.
Ar; outer electrons experience larger Zeff than those in As.
Ar; outer electrons experience smaller Zeff than those in As.
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Periodic
Properties
of the
Elements
A. The 2p electron removed from an oxygen atom is in a fully
occupied orbital with decreased electron-electron repulsions
compared to the one from a nitrogen atom.
B. The 2p electron removed from an oxygen atom is in a more than
half-filled subshell, which has extra stability compared to the one
from a nitrogen atom.
C. The 2p electron removed from an oxygen atom is in a fully
occupied orbital with increased electron-electron repulsions
compared to the one from a nitrogen atom.
Periodic
D. The 2p electron removed from an oxygen atom is in a lower energy
Properties
state compared to the one from a nitrogen atom.
of the
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Elements
Sample Exercise 7.6 Periodic Trends in Ionization Energy
Referring to a periodic table, arrange the atoms Ne, Na, P, Ar, K in order of increasing first ionization
energy.
FIGURE 7.9 Trends in first ionization energies
of the elements
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Periodic
Properties
of the
Elements
A.
B.
Same electron configurations: [Ar]3d3
Different electron configurations
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Periodic
Properties
of the
Elements
Sample Exercise 7.7 Electron Configurations of Ions
Write the electron configuration for (a) Ca2+, (b) Co3+, and (c) S2–.
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Periodic
Properties
of the
Elements
Electron Affinity
Electron affinity is the energy change
accompanying the addition of an
electron to a gaseous atom:
Cl + e−  Cl−
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Periodic
Properties
of the
Elements
Trends in Electron Affinity
In general, electron affinity
becomes more exothermic as
you go from left to right across a
row.
There are again, however, two
discontinuities in this trend.
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Periodic
Properties
of the
Elements
Trends in Electron Affinity
• The first occurs between
Groups IA and IIA.
– The added electron must
go in a p orbital, not an s
orbital.
– The electron is farther
from the nucleus and feels
repulsion from the s
electrons.
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Periodic
Properties
of the
Elements
Trends in Electron Affinity
• The second discontinuity
occurs between Groups IVA
and VA.
– Group VA has no empty
orbitals.
– The extra electron must go
into an already occupied
orbital, creating repulsion.
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Periodic
Properties
of the
Elements
A. Group 4A; outer electrons of atoms in this family
experience greater Zeff than the elements in other
families of the same period and this results in greater
attraction of an electron when electrons are added.
B. Group 5A; outer electrons of atoms in this family
experience greater Zeff than the elements in other
families of the same period and this results greater
attraction of an electron when electrons are added.
C. Group 6A; outer electrons of atoms in this family
experience greater Zeff than the elements in other
families of the same period and this results in greater
attraction of an electron when electrons are added.
D. Group 7A; outer electrons of atoms in this family
experience greater Zeff than the elements in other
families of the same period and this results in greater
attraction of an electron when an electron is added.
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Periodic
Properties
of the
Elements
A.
B.
C.
D.
EA for Cl is significantly more endothermic than IE1 for Cl.
IE1 for Cl– is significantly more exothermic than EA for Cl.
They are equal in magnitude and opposite in sign.
They are equal in magnitude and sign.
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Periodic
Properties
of the
Elements
Properties of Metal, Nonmetals,
and Metalloids
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Periodic
Properties
of the
Elements
A. Electron affinity is increasing from Ge to Sn and this correlates with increasing
metallic character.
B. Ionization energy is decreasing from Ge to Sn and this correlates with increasing
metallic character.
C. Atomic radius is decreasing from Ge to Sn and this correlates with increasing
metallic character.
Periodic
Properties
D. Number of valence electrons is increasing from Ge to Sn and this correlates with
of the
increasing metallic character.
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Elements
Metals versus Nonmetals
Differences between metals and nonmetals
tend to revolve around these properties.
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Periodic
Properties
of the
Elements
Metals versus Nonmetals
• Metals tend to form cations.
• Nonmetals tend to form anions.
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Periodic
Properties
of the
Elements
Metals
Metals tend to be
lustrous, malleable,
ductile, and good
conductors of heat
and electricity.
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Periodic
Properties
of the
Elements
A. Cations are to the right of the red line and anions are to the left
B. Higher oxidation states are adjacent to the red line and decrease
moving to the right or left, excluding the transition elements in
terms of trend in oxidation states.
C. Higher oxidation states are adjacent to the red line and increase
moving to the right or left, excluding the transition elements in
terms of trend in oxidation states.
D. There is no observable trend.
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Periodic
Properties
of the
Elements
A.
B.
C.
D.
There is no correlation between ionization energy and metallic
character.
Increasing ionization energy correlates with decreasing
metallic character.
Increasing ionization energy correlates with increasing
metallic character.
Decreasing ionization energy correlates with decreasing
metallic character.
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Periodic
Properties
of the
Elements
Metals
• Compounds formed between metals and
nonmetals tend to be ionic.
• Metal oxides tend to be basic.
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Periodic
Properties
of the
Elements
Sample Exercise 7.8 Metal Oxides
(a) Would you expect scandium oxide to be a solid, liquid, or gas at room temperature?
(b) Write the balanced chemical equation for the reaction of scandium oxide with nitric acid.
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Periodic
Properties
of the
Elements
Nonmetals
• Nonmetals are dull,
brittle substances that
are poor conductors
of heat and electricity.
• They tend to gain
electrons in reactions
with metals to acquire
a noble-gas
configuration.
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Periodic
Properties
of the
Elements
Nonmetals
• Substances containing only nonmetals are
molecular compounds.
• Most nonmetal oxides are acidic.
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Periodic
Properties
of the
Elements
A.
B.
C.
D.
Molecular and A is Sc.
Molecular and A is P.
Ionic and A is P.
Ionic and A is Sc.
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Periodic
Properties
of the
Elements
Sample Exercise 7.9 Nonmetal Oxides
Write the balanced chemical equation for the reaction of solid selenium dioxide, SeO2(s), with (a)
water, (b) aqueous sodium hydroxide.
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Periodic
Properties
of the
Elements
Metalloids
• Metalloids have
some characteristics
of metals and some
of nonmetals.
• For instance, silicon
looks shiny, but is
brittle and a fairly
poor conductor.
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Periodic
Properties
of the
Elements
Group Trends
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Periodic
Properties
of the
Elements
Alkali Metals
• Alkali metals are
soft, metallic solids.
• The name comes
from the Arabic
word for ashes.
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Periodic
Properties
of the
Elements
Alkali Metals
• They are found only in compounds in nature,
not in their elemental forms.
• They have low densities and melting points.
• They also have low ionization energies.
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Periodic
Properties
of the
Elements
Alkali Metals
Their reactions with water are famously exothermic.
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Periodic
Properties
of the
Elements
Alkali Metals
• Alkali metals (except Li) react with oxygen to form
peroxides.
• K, Rb, and Cs also form superoxides:
K + O2  KO2
• They produce bright colors when placed in a flame.
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Periodic
Properties
of the
Elements
A.
B.
C.
D.
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Red
Yellow
Lilac
Green
Periodic
Properties
of the
Elements
A.
B.
C.
D.
Cs has the lowest ionization energy of the alkali metals.
Cs has the greatest density of the alkali metals.
Cs is the most conductive of the alkali metals.
Cs has the most electrons of the alkali metals.
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Periodic
Properties
of the
Elements
Sample Exercise 7.10 Reactions of an Alkali Metal
Write a balanced equation for the reaction of cesium metal with (a) Cl2(g), (b) H2O(l), (c) H2(g).
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Periodic
Properties
of the
Elements
Alkaline Earth Metals
• Alkaline earth metals have higher densities
and melting points than alkali metals.
• Their ionization energies are low, but not as
low as those of alkali metals.
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Periodic
Properties
of the
Elements
Alkaline Earth Metals
• Beryllium does not react
with water, and
magnesium reacts only
with steam, but the
other alkaline earth
metals react readily with
water.
• Reactivity tends to
increase as you go
down the group.
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Periodic
Properties
of the
Elements
A.
B.
C.
D.
CaCO3 is a very poor source of calcium due to its poor
solubility in water.
The dissolution reaction of metal carbonates is catalyzed by
enzymes in the intestines.
Metal carbonates are soluble in the acidic environment of the
stomach.
Metal carbonate solids can be directly passed into the skeletal
Periodic
system from the stomach.
Properties
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of the
Elements
Group 6A
• Oxygen, sulfur, and selenium are nonmetals.
• Tellurium is a metalloid.
Periodic
• The radioactive polonium is a metal.
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Properties
of the
Elements
A.
B.
C.
D.
400 nm is highest wavelength of visible light and corresponds to the
the lowest energy to break bonds. Assume it is minimal energy
required to break O—O bonds and calculate.
400 nm is lowest wavelength of visible light and corresponds to the
the lowest energy to break bonds. Assume it is minimal energy
required to break O—O bonds and calculate.
750 nm is lowest wavelength of visible light and corresponds to the
the lowest energy to break bonds. Assume it is minimal energy
required to break O—O bonds and calculate.
750 nm is highest wavelength of visible light and corresponds to the
the lowest energy to break bonds. Assume it is minimal energy
Periodic
required to break O—O bonds and calculate.
Properties
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of the
Elements
Sulfur
• Sulfur is a weaker
oxidizer than
oxygen.
• The most stable
allotrope is S8, a
ringed molecule.
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Periodic
Properties
of the
Elements
Group VIIA: Halogens
• The halogens are prototypical nonmetals.
• The name comes from the Greek words halos
and gennao: “salt formers.”
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Periodic
Properties
of the
Elements
A.
B.
C.
D.
Halogens are larger atoms than S and Se and would form an
unstable, crowded X8 structure..
Halogens have the valence configuration ns2np6 and only
need to share one pair of electrons to form a stable bond.
Halogens with 7 valence electrons prefer to form X7
compounds.
Halogens with np6 outer orbitals prefer to form X6 compounds.
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Periodic
Properties
of the
Elements
Group VIIA: Halogens
• They have large, negative
electron affinities.
– Therefore, they tend to oxidize
other elements easily.
• They react directly with
metals to form metal halides.
• Chlorine is added to water
supplies to serve as a
disinfectant.
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Periodic
Properties
of the
Elements
Group VIIIA: Noble Gases
• The noble gases have astronomical ionization
energies.
• Their electron affinities are positive.
– Therefore, they are relatively unreactive.
• They are found as monatomic gases.
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Periodic
Properties
of the
Elements
A.
It is not possible to use the data in Table 7.7 to determine the
characteristics of astatine.
B.
Yes, by extrapolating from the other data, we can estimate that the
atomic radius is approximately 1.10 angstroms and I1 must be
approximately 1000 kJ/mol.
C. Yes, by extrapolating from the other data, we can estimate that the Periodic
Properties
atomic radius is approximately 1.5 angstroms and I1 must be
of the
approximately 900 kJ/mol.
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Elements