Development of Periodic Development of Periodic TableTable
Elements in the Elements in the same group same group generally have generally have similar chemical similar chemical properties.properties.
Properties are Properties are not identical, not identical, however.however.
Development of Periodic Development of Periodic TableTable
Dmitri Dmitri Mendeleev and Mendeleev and Lothar Meyer Lothar Meyer independently independently came to the came to the same same conclusion conclusion about how about how elements elements should be should be grouped.grouped.
Development of Periodic Development of Periodic TableTable
Mendeleev, for instance, predicted the Mendeleev, for instance, predicted the discovery of germanium (which he called discovery of germanium (which he called eka-silicon) as an element with an eka-silicon) as an element with an atomic weight between that of zinc and atomic weight between that of zinc and arsenic, but with chemical properties arsenic, but with chemical properties similar to those of silicon.similar to those of silicon.
Periodic TrendsPeriodic Trends
In this chapter, we will In this chapter, we will rationalize observed trends inrationalize observed trends in Sizes of atoms and ions.Sizes of atoms and ions. Ionization energy.Ionization energy. Electron affinity.Electron affinity.
Effective Nuclear ChargeEffective Nuclear Charge
In a many-electron In a many-electron atom, electrons are atom, electrons are both attracted to the both attracted to the nucleus and repelled nucleus and repelled by other electrons.by other electrons.
The nuclear charge The nuclear charge that an electron that an electron experiences depends experiences depends on both factors.on both factors.
Effective Nuclear ChargeEffective Nuclear Charge
The effective The effective nuclear charge, nuclear charge, ZZeffeff, , is found this way:is found this way:
ZZeffeff = = ZZ −− SS
where where ZZ is the is the atomic number and atomic number and SS is a screening is a screening constant, usually constant, usually close to the number close to the number of inner electrons.of inner electrons.
Sizes of AtomsSizes of Atoms
The bonding The bonding atomic radius is atomic radius is defined as one-defined as one-half of the half of the distance between distance between covalently covalently bonded nuclei.bonded nuclei.
Sizes of AtomsSizes of Atoms
Bonding atomic Bonding atomic radius tends to… radius tends to… ……decrease from decrease from
left to right left to right across a rowacross a rowdue to increasing due to increasing ZZeffeff..
……increase from top increase from top to bottom of a to bottom of a columncolumndue to increasing due to increasing
value of value of nn
Sizes of IonsSizes of Ions
Ionic size Ionic size depends upon:depends upon: Nuclear Nuclear
charge.charge. Number of Number of
electrons.electrons. Orbitals in Orbitals in
which which electrons electrons reside.reside.
Sizes of IonsSizes of Ions
Cations are Cations are smaller than smaller than their parent their parent atoms.atoms. The outermost The outermost
electron is electron is removed and removed and repulsions are repulsions are reduced.reduced.
Sizes of IonsSizes of Ions
Anions are Anions are larger than larger than their parent their parent atoms.atoms. Electrons are Electrons are
added and added and repulsions are repulsions are increased.increased.
Sizes of IonsSizes of Ions
Ions increase in Ions increase in size as you go size as you go down a column.down a column. Due to increasing Due to increasing
value of value of nn..
Sizes of IonsSizes of Ions
In an In an isoelectronic seriesisoelectronic series, ions have , ions have the same number of electrons.the same number of electrons.
Ionic size decreases with an Ionic size decreases with an increasing nuclear charge.increasing nuclear charge.
Ionization EnergyIonization Energy
Amount of energy required to Amount of energy required to remove an electron from the remove an electron from the ground state of a gaseous atom or ground state of a gaseous atom or ion.ion. First ionization energy is that energy First ionization energy is that energy
required to remove first electron.required to remove first electron. Second ionization energy is that Second ionization energy is that
energy required to remove second energy required to remove second electron, etc.electron, etc.
Ionization EnergyIonization Energy
It requires more energy to remove It requires more energy to remove each successive electron.each successive electron.
When all valence electrons have been When all valence electrons have been removed, the ionization energy takes removed, the ionization energy takes a quantum leap.a quantum leap.
Trends in First Ionization Trends in First Ionization EnergiesEnergies
As one goes down As one goes down a column, less a column, less energy is required energy is required to remove the first to remove the first electron.electron. For atoms in the For atoms in the
same group, same group, ZZeffeff is is essentially the essentially the same, but the same, but the valence electrons valence electrons are farther from the are farther from the nucleus.nucleus.
Trends in First Ionization Trends in First Ionization EnergiesEnergies
Generally, as one Generally, as one goes across a goes across a row, it gets row, it gets harder to remove harder to remove an electron.an electron. As you go from As you go from
left to right, left to right, ZZeffeff increases.increases.
Trends in First Ionization Trends in First Ionization EnergiesEnergies
However, there However, there are two apparent are two apparent discontinuities in discontinuities in this trend.this trend.
Trends in First Ionization Trends in First Ionization EnergiesEnergies
The first occurs The first occurs between Groups between Groups IIA and IIIA.IIA and IIIA.
Electron removed Electron removed from from pp-orbital -orbital rather than rather than ss--orbitalorbital Electron farther Electron farther
from nucleusfrom nucleus Small amount of Small amount of
repulsion by repulsion by ss electrons.electrons.
Trends in First Ionization Trends in First Ionization EnergiesEnergies
The second occurs The second occurs between Groups between Groups VA and VIA.VA and VIA. Electron removed Electron removed
comes from doubly comes from doubly occupied orbital.occupied orbital.
Repulsion from Repulsion from other electron in other electron in orbital helps in its orbital helps in its removal.removal.
Electron AffinityElectron Affinity
Energy change accompanying addition Energy change accompanying addition of electron to gaseous atom:of electron to gaseous atom:
Cl + eCl + e−− Cl Cl−−
Trends in Electron Trends in Electron AffinityAffinity
In general, In general, electron affinity electron affinity becomes more becomes more exothermic as exothermic as you go from left you go from left to right across a to right across a row.row.
Trends in Electron Trends in Electron AffinityAffinity
There are There are again, again, however, two however, two discontinuitidiscontinuities in this es in this trend.trend.
Trends in Electron Trends in Electron AffinityAffinity
The first occurs The first occurs between Groups between Groups IA and IIA.IA and IIA. Added electron Added electron
must go in must go in pp--orbital, not orbital, not ss--orbital.orbital.
Electron is farther Electron is farther from nucleus and from nucleus and feels repulsion feels repulsion from from ss-electrons.-electrons.
Trends in Electron Trends in Electron AffinityAffinity
The second occurs The second occurs between Groups between Groups IVA and VA.IVA and VA. Group VA has no Group VA has no
empty orbitals.empty orbitals. Extra electron Extra electron
must go into must go into occupied orbital, occupied orbital, creating repulsion.creating repulsion.
Metals versus NonmetalsMetals versus Nonmetals
Differences between metals and Differences between metals and nonmetals tend to revolve around nonmetals tend to revolve around these properties.these properties.
Metals versus NonmetalsMetals versus Nonmetals
Metals tend to form cations.Metals tend to form cations. Nonmetals tend to form anions.Nonmetals tend to form anions.
MetalsMetals
Tend to be Tend to be lustrous, lustrous, malleable, malleable, ductile, and good ductile, and good conductors of conductors of heat and heat and electricity.electricity.
MetalsMetals
Compounds Compounds formed between formed between metals and metals and nonmetals tend nonmetals tend to be ionic.to be ionic.
Metal oxides Metal oxides tend to be basic.tend to be basic.
NonmetalsNonmetals Dull, brittle Dull, brittle
substances that substances that are poor are poor conductors of conductors of heat and heat and electricity.electricity.
Tend to gain Tend to gain electrons in electrons in reactions with reactions with metals to acquire metals to acquire noble gas noble gas configuration.configuration.
NonmetalsNonmetals
Substances Substances containing only containing only nonmetals are nonmetals are molecular molecular compounds.compounds.
Most nonmetal Most nonmetal oxides are acidic.oxides are acidic.
MetalloidsMetalloids
Have some Have some characteristics of characteristics of metals, some of metals, some of nonmetals.nonmetals.
For instance, For instance, silicon looks silicon looks shiny, but is shiny, but is brittle and fairly brittle and fairly poor conductor.poor conductor.
Alkali MetalsAlkali Metals
Soft, metallic Soft, metallic solids.solids.
Name comes Name comes from Arabic word from Arabic word for ashes.for ashes.
Alkali MetalsAlkali Metals
Found only as compounds in nature.Found only as compounds in nature. Have low densities and melting Have low densities and melting
points.points. Also have low ionization energies.Also have low ionization energies.
Alkali MetalsAlkali Metals
Their reactions with water are famously Their reactions with water are famously exothermic.exothermic.
Alkali MetalsAlkali Metals
Alkali metals (except Li) react with Alkali metals (except Li) react with oxygen to form peroxides.oxygen to form peroxides.
K, Rb, and Cs also form superoxides:K, Rb, and Cs also form superoxides:
K + OK + O22 KO KO22
Produce bright colors when placed in Produce bright colors when placed in flame.flame.
Alkaline Earth MetalsAlkaline Earth Metals
Have higher densities and melting Have higher densities and melting points than alkali metals.points than alkali metals.
Have low ionization energies, but not Have low ionization energies, but not as low as alkali metals.as low as alkali metals.
Alkaline Earth MetalsAlkaline Earth Metals
BeBe does not react does not react with water, Mg with water, Mg reacts only with reacts only with steam, but others steam, but others react readily with react readily with water.water.
Reactivity tends Reactivity tends to increase as go to increase as go down group.down group.
Group 6AGroup 6A
Oxygen, sulfur, and selenium are Oxygen, sulfur, and selenium are nonmetals.nonmetals.
Tellurium is a metalloid.Tellurium is a metalloid. The radioactive polonium is a metal.The radioactive polonium is a metal.
OxygenOxygen
Two allotropes:Two allotropes: OO22
OO33, ozone, ozone Three anions:Three anions:
OO22−−, oxide, oxide OO22
22−−, peroxide, peroxide OO22
11−−, superoxide, superoxide Tends to take Tends to take
electrons from other electrons from other elements (oxidation)elements (oxidation)
SulfurSulfur
Weaker oxidizing Weaker oxidizing agent than agent than oxygen.oxygen.
Most stable Most stable allotrope is Sallotrope is S88, a , a ringed molecule.ringed molecule.
Group VIIA: HalogensGroup VIIA: Halogens
Prototypical nonmetalsPrototypical nonmetals Name comes from the Greek Name comes from the Greek haloshalos
and and gennaogennao: “salt formers”: “salt formers”
Group VIIA: HalogensGroup VIIA: Halogens
Large, negative Large, negative electron affinitieselectron affinities Therefore, tend to Therefore, tend to
oxidize other elements oxidize other elements easilyeasily
React directly with React directly with metals to form metal metals to form metal halideshalides
Chlorine added to Chlorine added to water supplies to serve water supplies to serve as disinfectantas disinfectant
Group VIIIA: Noble Group VIIIA: Noble GasesGases
Astronomical ionization energiesAstronomical ionization energies Positive electron affinitiesPositive electron affinities
Therefore, relatively unreactiveTherefore, relatively unreactive Monatomic gasesMonatomic gases
Group VIIIA: Noble Group VIIIA: Noble GasesGases
Xe forms three Xe forms three compounds:compounds: XeFXeF22
XeFXeF44 (at right) (at right) XeFXeF66
Kr forms only one Kr forms only one stable compound:stable compound: KrFKrF22
The unstable HArF The unstable HArF was synthesized in was synthesized in 2000.2000.