chapter 7 periodic properties of the elements · periodic properties of the elements chemistry, the...
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![Page 1: Chapter 7 Periodic Properties of the Elements · Periodic Properties of the Elements Chemistry, The Central Science, 11th edition Theodore L. Brown; ... Chapter 7 Periodic Properties](https://reader030.vdocuments.mx/reader030/viewer/2022012317/5b85130d7f8b9aec488d8f82/html5/thumbnails/1.jpg)
PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Chapter 7Periodic Properties
of the Elements
Chemistry, The Central Science, 11th editionTheodore L. Brown; H. Eugene LeMay, Jr.;
and Bruce E. Bursten
John D. BookstaverSt. Charles Community College
Cottleville, MO
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Development of Periodic Table
• Elements in the same group generally have similar chemical properties.
• Physical properties are not necessarily similar, however.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
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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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Development of 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.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Periodic Trends
• In this chapter, we will rationalize observed trends in– Sizes of atoms and ions.– Ionization energy.– Electron affinity.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
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.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Effective Nuclear Charge
The effective nuclear charge, Zeff, is found this way:
Zeff = Z − Swhere Z is the atomic number and S is a screening constant, usually close to the number of inner electrons.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
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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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Sizes of Atoms
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 increasing value of n).
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Sizes of Ions
• Ionic size depends upon:– The nuclear
charge.– The number of
electrons.– The orbitals in
which electrons reside.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Sizes of Ions
• Cations are smaller than their parent atoms.– The outermost
electron is removed and repulsions between electrons are reduced.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Sizes of Ions
• Anions are larger than their parent atoms.– Electrons are
added and repulsions between electrons are increased.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Sizes of Ions
• Ions increase in size as you go down a column.– This is due to
increasing value of n.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
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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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
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 first electron.– The second ionization energy is that
energy required to remove second electron, etc.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
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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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
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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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
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.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Trends in First Ionization Energies
However, there are two apparent discontinuities in this trend.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
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 nucleus.– There is also a small
amount of repulsion by the s electrons.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Trends in First Ionization Energies
• The second occurs between Groups VA and VIA.– The electron removed
comes from doubly occupied orbital.
– Repulsion from the other electron in the orbital aids in its removal.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
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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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Trends in Electron Affinity
In general, electron affinity becomes more exothermic as you go from left to right across a row.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Trends in Electron Affinity
There are again, however, two discontinuities in this trend.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
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 nucleus and feels repulsion from the s-electrons.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Trends in Electron Affinity
• The second 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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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Properties of Metal, Nonmetals,and Metalloids
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Metals versus Nonmetals
Differences between metals and nonmetals tend to revolve around these properties.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Metals versus Nonmetals
• Metals tend to form cations.• Nonmetals tend to form anions.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Metals
They tend to be lustrous, malleable, ductile, and good conductors of heat and electricity.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Metals
• Compounds formed between metals and nonmetals tend to be ionic.
• Metal oxides tend to be basic.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Nonmetals
• These 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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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Nonmetals
• Substances containing only nonmetals are molecular compounds.
• Most nonmetal oxides are acidic.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Metalloids
• These have some characteristics of metals and some of nonmetals.
• For instance, silicon looks shiny, but is brittle and fairly poor conductor.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Group Trends
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Alkali Metals
• Alkali metals are soft, metallic solids.
• The name comes from the Arabic word for ashes.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
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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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Alkali Metals
Their reactions with water are famously exothermic.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
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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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
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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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Alkaline Earth Metals
• Beryllium does not react with water and magnesium reacts only with steam, but the others react readily with water.
• Reactivity tends to increase as you go down the group.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Group 6A
• Oxygen, sulfur, and selenium are nonmetals.• Tellurium is a metalloid.• The radioactive polonium is a metal.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Oxygen• There are two allotropes of
oxygen:– O2– O3, ozone
• There can be three anions:– O2−, oxide– O2
2−, peroxide– O2
1−, superoxide• It tends to take electrons
from other elements (oxidation).
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Sulfur
• Sulfur is a weaker oxidizer than oxygen.
• The most stable allotrope is S8, a ringed molecule.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Group VIIA: Halogens
• The halogens are prototypical nonmetals.• The name comes from the Greek words halos
and gennao: “salt formers”.
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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
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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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
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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PeriodicProperties
of the Elements
© 2009, Prentice-Hall, Inc.
Group VIIIA: Noble Gases
• Xe forms three compounds:– XeF2
– XeF4 (at right)– XeF6
• Kr forms only one stable compound:– KrF2
• The unstable HArF was synthesized in 2000.