chem 101 week 9 ch8
TRANSCRIPT
![Page 1: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/1.jpg)
Chapter 8Periodic Relationships Among the Elements
![Page 2: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/2.jpg)
Development of Periodic Table
• Elements in the same group generally have similar chemical properties.
• Properties are not identical, however.
![Page 3: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/3.jpg)
Development of Periodic Table
Dmitri Mendeleev and Lothar Meyer independently came to the same conclusion about how elements should be grouped.
![Page 4: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/4.jpg)
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.
![Page 5: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/5.jpg)
Periodic Trends
• In this chapter, we will rationalize observed trends in– Sizes of atoms and ions.– Ionization energy.– Electron affinity.
• To do so, however, we must first understand……..
![Page 6: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/6.jpg)
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.
![Page 7: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/7.jpg)
Effective Nuclear Charge
The effective nuclear charge, Zeff, is found this way:
Zeff = Z − σwhere Z is the atomic number and σ (sigma) is a shielding or screening constant, usually close to the number of inner electrons.
![Page 8: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/8.jpg)
Sizes of Atoms
The bonding atomic radius is defined as one-half of the distance between covalently bonded nuclei.
![Page 9: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/9.jpg)
Sizes of Atoms
Bonding atomic radius tends to… …decrease from left to
right across a rowdue to increasing Zeff.
…increase from top to bottom of a column
due to increasing value of n
![Page 10: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/10.jpg)
Sizes of Ions
• Ionic size depends upon:– Nuclear charge.– Number of
electrons.– Orbitals in which
electrons reside.
![Page 11: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/11.jpg)
Sizes of Ions
• Cations are smaller than their parent atoms.– The outermost
electron is removed and repulsions are reduced.
![Page 12: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/12.jpg)
Sizes of Ions
• Anions are larger than their parent atoms.– Electrons are added
and repulsions are increased.
![Page 13: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/13.jpg)
Sizes of Ions
• Ions increase in size as you go down a column.– Due to increasing value
of n.
![Page 14: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/14.jpg)
Sizes of Ions
• In an isoelectronic series, ions have the same number of electrons.
• Ionic size decreases with an increasing nuclear charge.
![Page 15: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/15.jpg)
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.
![Page 16: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/16.jpg)
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.
![Page 17: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/17.jpg)
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.
![Page 18: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/18.jpg)
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.
![Page 19: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/19.jpg)
Trends in First Ionization Energies
However, there are two apparent discontinuities in this trend.
![Page 20: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/20.jpg)
Trends in First Ionization Energies
• The first occurs between Groups IIA and IIIA.
• Electron removed from p-orbital rather than s-orbital– Electron farther from
nucleus– Small amount of repulsion
by s electrons.
![Page 21: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/21.jpg)
Trends in First Ionization Energies
• The second occurs between Groups VA and VIA.– Electron removed comes
from doubly occupied orbital.
– Repulsion from other electron in orbital helps in its removal.
![Page 22: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/22.jpg)
Electron Affinity
Energy change accompanying addition of electron to gaseous atom:
Cl + e− Cl−
![Page 23: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/23.jpg)
Trends in Electron Affinity
In general, electron affinity becomes more exothermic as you go from left to right across a row.
![Page 24: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/24.jpg)
Trends in Electron Affinity
There are again, however, two discontinuities in this trend.
![Page 25: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/25.jpg)
Trends in Electron Affinity
• The first occurs between Groups IA and IIA.– Added electron must
go in p-orbital, not s-orbital.
– Electron is farther from nucleus and feels repulsion from s-electrons.
![Page 26: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/26.jpg)
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.
![Page 27: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/27.jpg)
Properties of Metal, Nonmetals,and Metalloids
![Page 28: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/28.jpg)
Metals versus Nonmetals
Differences between metals and nonmetals tend to revolve around these properties.
![Page 29: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/29.jpg)
Metals versus Nonmetals
• Metals tend to form cations.• Nonmetals tend to form anions.
![Page 30: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/30.jpg)
Metals
Tend to be lustrous, malleable, ductile, and good conductors of heat and electricity.
![Page 31: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/31.jpg)
Metals
• Compounds formed between metals and nonmetals tend to be ionic.
• Metal oxides tend to be basic.
![Page 32: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/32.jpg)
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.
![Page 33: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/33.jpg)
Nonmetals
• Substances containing only nonmetals are molecular compounds.
• Most nonmetal oxides are acidic.
![Page 34: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/34.jpg)
Metalloids
• Have some characteristics of metals, some of nonmetals.
• For instance, silicon looks shiny, but is brittle and fairly poor conductor.
![Page 35: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/35.jpg)
Group Trends
![Page 36: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/36.jpg)
Alkali Metals
• Soft, metallic solids.• Name comes from
Arabic word for ashes.
![Page 37: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/37.jpg)
Alkali Metals
• Found only as compounds in nature.• Have low densities and melting points.• Also have low ionization energies.
![Page 38: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/38.jpg)
Alkali Metals
Their reactions with water are famously exothermic.
![Page 39: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/39.jpg)
Alkali Metals• 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.
![Page 40: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/40.jpg)
Alkaline Earth Metals
• Have higher densities and melting points than alkali metals.
• Have low ionization energies, but not as low as alkali metals.
![Page 41: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/41.jpg)
Alkaline Earth Metals
• Be does not react with water, Mg reacts only with steam, but others react readily with water.
• Reactivity tends to increase as go down group.
![Page 42: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/42.jpg)
Group 6A
• Oxygen, sulfur, and selenium are nonmetals.• Tellurium is a metalloid.• The radioactive polonium is a metal.
![Page 43: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/43.jpg)
Oxygen
• Two allotropes:– O2
– O3, ozone• Three anions:– O2−, oxide– O2
2−, peroxide– O2
1−, superoxide• Tends to take electrons
from other elements (oxidation)
![Page 44: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/44.jpg)
Sulfur
• Weaker oxidizing agent than oxygen.
• Most stable allotrope is S8, a ringed molecule.
![Page 45: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/45.jpg)
Group VIIA: Halogens
• Prototypical nonmetals• Name comes from the Greek halos and gennao:
“salt formers”
![Page 46: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/46.jpg)
Group VIIA: Halogens
• 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
![Page 47: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/47.jpg)
Group VIIIA: Noble Gases
• Astronomical ionization energies• Positive electron affinities– Therefore, relatively unreactive
• Monatomic gases
![Page 48: Chem 101 week 9 ch8](https://reader036.vdocuments.us/reader036/viewer/2022062514/558e582e1a28ab496e8b46da/html5/thumbnails/48.jpg)
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.