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Periodic Chapter Properties of the Elements
Development of Periodic Table
Dmitri Mendeleev and Lothar Meyer independently came to the same conclusion about how elements should be grouped.
Elements in the same group generally have similar chemical properties.
Properties are not identical, however.
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Periodic Trends
In this chapter, we will observe trends in Sizes of atoms and ions. Ionization energy. Electron affinity.
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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Effective Nuclear Charge
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.
Fig 7.3
Sizes of Atoms
The bonding atomic radius is defined as one-half of the distance between covalently bonded nuclei.
Fig 7.5
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Sizes of Atoms
Bonding atomic radius tends to ...increase from top to bottom of a column due to
increasing value of n Fig 7.6
Bonding atomic radius tends to...decrease from
left to right across a row
Sizes of Ions
Ionic size depends upon:
Nuclear charge. Number of electrons. Orbitals in which electrons reside.
Fig 7.7
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Sizes of Ions
Cations are smaller than their parent atoms. The outermost electron is removed and repulsions are reduced.
Fig 7.7
Sizes of Ions
Anions are larger than their parent atoms. Electrons are added and repulsions are increased.
Fig 7.7
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Sizes of Ions
Ions increase in size as you go down a column.
Due to increasing value of n.
Fig 7.7
Sizes of Ions
In an isoelectronic series, ions have the same number of electrons. Ionic size decreases with an increasing nuclear charge.
Fig 7.7
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Ionization Energy
Amount of energy required to remove an electron from the ground state of a gaseous atom or ion.
First ionization energy is that energy required to remove first electron. Second ionization energy is that energy required to remove second electron, etc.
Ionization Energy
It requires more energy to remove each successive electron.
Table 7.2
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Trends in First Ionization Energies
Generally, as one goes across a row, it gets harder to remove an electron. However, there are two apparent discontinuities in this trend.
Fig 7.10
Trends in First Ionization Energies
The first occurs between Groups IIA and IIIA. Electron removed from p-orbital rather than sorbital
Electron farther from nucleus Small amount of repulsion by s electrons.
Fig 7.10
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Trends in First Ionization Energies
The second occurs between Groups VA and VIA.
Electron removed comes from doubly occupied orbital. Repulsion from electron other in orbital helps in its removal. Fig 7.10
Electron Affinity
Energy change accompanying addition of electron to gaseous atom: Cl + e- Cl-
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Trends in Electron Affinity
Two discontinuities in this trend.
Fig 7.12
The first occurs between Groups IA and IIA.
Added electron must go in p-orbital, not sorbital. Electron is farther from nucleus and feels repulsion from selectrons.
Trends in Electron Affinity
The second occurs between Groups IVA and VA.
Group VA has no empty orbitals. Extra electron must go into occupied orbital, creating repulsion.
Fig 7.12
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Properties of Metal, Nonmetals, and Metalloids
Fig 7.13
Metals versus Nonmetals
Metals tend to form cations. Nonmetals tend to form anions.
Fig 7.15
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Metals
Tend to be lustrous, malleable, ductile, and good conductors of heat and electricity.
Metals
Compounds formed between metals and nonmetals tend to be ionic. Metal oxides tend to be basic.
green solution
NiO(s)+2HNO3(aq)
Ni(NO3)2(aq) + H2O(l)
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Nonmetals
Dull, brittle substances that are poor conductors of heat and electricity. Tend to gain electrons in reactions with metals to acquire noble gas configuration.
Nonmetals (cont)
- Most nonmetal oxides are acidic - The nonmetal oxides that dissolve in water react to form acids
Nonmetal oxide + water
acid
Example: CO2 + H2O(l) P4O10 + 6 H2O(l) H2CO3 4 H3PO4
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Metalloids
Have some characteristics of metals, some of nonmetals. For instance, silicon looks shiny, but is brittle and fairly poor conductor.
Group Trends
Alkali Metals
Soft, metallic solids. Name comes from Arabic word for ashes.
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Alkali Metals (cont)
Found only as compounds in nature. Have low densities and melting points. Also have low ionization energies.
Table 7.4
Alkali Metals (cont)
Alkali metals (except Li) react with oxygen to form peroxides. K, Rb, and Cs also form superoxides: K + O2 KO2 Produce bright colors when placed in flame.
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Alkaline Earth Metals
Table 7.5
Have higher densities and melting points than alkali metals. Have low ionization energies, but not as low as alkali metals.
Group 6A
Table 7.6
Oxygen, sulfur, and selenium are nonmetals. Tellurium is a metalloid. The radioactive polonium is a metal.
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Group VIIA: Halogens
Table 7.7
Large, negative electron affinities
Therefore, tend to oxidize other elements easily
React directly with metals to form metal halides Chlorine added to water supplies to serve as disinfectant
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Group VIIIA: Noble Gases
Astronomical ionization energies Positive electron affinities Therefore, relatively unreactive Monatomic gases
Table 7.8
End
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Practice exercises 7.37, 7.29, 7.31, 7.33, 7.41, 7.43, 7.45 7.57, 7.79, 7.51, 7.63
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