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Instructor: Dr. Robert Powers OfficeAddress: 722 HaHPhone: 472-3039e-mail:rpowers3@unl.edu
web page: http://bionmr-c1.unl.eduhttp://bionmr-c1.unl.edu
September 11, 2001
NEVER FORGET
Periodic Table Chemical Trends
Periodicity in chemical properties is the basis of the periodic table arrangement
Periodicity of electron configuration:
- Affects attraction of atom for its valence electrons
- Affects attraction of valence electrons for additional electrons
Determines chemical Determines chemical and physical properties and physical properties of the elementsof the elements
Periodic Table
Copper (solid)
Mercury (liquid)
Chemical Trends
Hydrogen (gas)
1s1
[Ar]3d104s1
[Xe]5d106s2
Periodic Table Chemical Trends
1.) Chemical trends based on the combination of the electron configuration, octet rule and electronegativity
2.) Electronegativitya.) tendency to attract electrons in a compoundb.) empirically based range from 0.7 to 3.98
Attracts electrons
Donate electrons
Periodic Table Chemical Trends
1.) Chemical trends based on the combination of the electron configuration, octet rule and electronegativity
2.) ElectronegativityHigh electronegativity pulls electrons away from elements with weaker electronegativity
Low electronegativity easily loses electrons to elements with higher electronegativity
Periodic Table Chemical Trends
1.) Chemical trends based on the combination of the electron configuration, octet rule and electronegativity
3.) The Octet Rule
The representative elements achieve a noble-gas configuration (eight valence electrons) in most of their compounds, except hydrogen, which only has two valence electrons in its corresponding noble gas structure.
Periodic Table Chemical Trends
4.) Chemical reactions between Group IA elements and Group VIIA elements Group IA – single valence electron easily removed noble configuration Group VIIA – easily attracts one electron noble configuration (ns2p6) Form 1:1 ionic compound where Group IA loses e- and Group VIIA gains e-
Ionic compounds are usually solids
ns1 ns2p5
low
high
Chemical Trends
5.) Electronegativity differences determine the outcome of a chemical reaction Electronegativity of Chlorine is 3.16 Electronegativity of Bromine is 2.96
Halogen ions have an octet in valence shell
No need to share e-
Periodic Table
clear pale yellow dark brown clear
2Br- has sixteen valence electrons (eight each)
Br2 has only fourteen valence electrons
Two electrons lost from two Br-
Two electrons gained by Cl2 to form 2Cl-
The greater electronegativity of chlorine captures an electron from bromide
Periodic Table Chemical Trends
6.) Example: electronegativity difference determines chemical productsHalides are expected to react similarly with water, but there are some important differences. Why?
Answer:electronegativities: chlorine 3.16, oxygen 3.4, fluorine 3.98
fluorine can attract e- from oxygen- HF : eight valence electrons- O2 : six valence electrons
chlorine can not attract e- from oxygen, instead attracts e- from hydrogen in water and replaces hydrogen in water
- HCl : eight valence electrons- HOCl : Cl replaces H in water
Clicker Question
Clicker Question:What is a main factor that results in an atom having an increasing What is a main factor that results in an atom having an increasing
atomic radius compared to its neighbor?atomic radius compared to its neighbor?
a) total number of electrons
b) total number of protons and neutrons
c) total number of electrons in the outer electron shell
d) total number of electron shells
Periodic Table Chemical Trends
7.) Size of AtomAtomic radius – radius of the sphere containing 90% of the electron density for the
free atom related to electronic configurationProgressing from period to period
the valence shell is increasing far from the nucleus increased separation of negatively charged electrons from positive
charged protons Size of the atoms and ions increase
Incr
easi
ng
Ato
mic
Rad
ius
Periodic Table Chemical Trends
7.) Size of AtomProgressing from group to group
the valence shell is a constant increased attraction between the negatively charged electrons from
positive charged protons all e- are drawn to the nucleus Size of the atoms and ions decrease despite adding electrons Minimal size change occurs for transition elements
- fill inner shell d-orbitals that shield outer shell s-orbitalsDecreasing Atomic Radius
Periodic Table Chemical Trends
7.) Size of AtomChanges in Size Affects Chemical Behavior
Decrease in RadiusIncrease in attractionbetween nucleus and
electrons
Increase in:ionization energy electron affinityelectronegativity
Periodic Table Chemical Trends
8.) Size of IonWhen an atom gains or loses an electron, the ion is a different size than the neutral atom
Like Charges Repel:
Remove e- remove repulsion smallerpositive charged ion (cation) is smaller
Add e- add repulsion largernegatively charged ion (anion) is larger
Size difference can be dramatic, about a factor of 2
Periodic Table Chemical Trends
8.) Size of IonWhen an atom gains or loses an electron, the ion is a different size than the neutral atom
Like Charges Repel:
Isoelectronic ions are bigger the greater the negative chargeAgain, greater nuclear charge can hold electrons closer than smaller nuclear charge
2s22p6: 7N3- > 8O2- > 9F- > 11Na+ > 12Mg2+ > 13Al3+
171 140 133 102 72 50 picometers (pm)
Periodic Table Chemical Trends
9.) Example: converting mass density to molar and atomic densityGiven a density of 5.54 g/cm3 for titanium (Ti) and a density of 7.874 g/cm3 for iron (Fe), calculate the atomic density and atomic radius in the metals if Ti occupies 74% of the volume and Fe occupies 68% of the volume.
33
cm/molmol/g
cm/g
massatomic
densitymassvolume/molesdensityMolar
33
116086747
545
86747
cm/mol.mol/g.
cm/g.densitymolar
mol/g.massatomic
:Ti
33
116084555
8747
84555
cm/mol.mol/g.
cm/g.densitymolar
mol/g.massatomic
:Fe
Solution:Calculate Molar
Density:
Periodic Table Chemical Trends
9.) Example: converting mass density to molar and atomic densityGiven a density of 5.54 g/cm3 for titanium (Ti) and a density of 7.874 g/cm3 for iron (Fe), calculate the atomic density and atomic radius in the metals if Ti occupies 74% of the volume and Fe occupies 68% of the volume.
Solution:Calculate
Atomic Density:3
3cm/atoms
mol
atomsx
mol/g
cm/gmole/atoms
massatomic
densitymassvolume/atomsdensityAtomic
322233 109961002213761160 cm/atoms.mol/atomsx.cm/mol. :Ti
322233 10491810022137614100 cm/atoms.mol/atomsx.cm/mol. :Fe
Periodic Table Chemical Trends
9.) Example: converting mass density to molar and atomic densityGiven a density of 5.54 g/cm3 for titanium (Ti) and a density of 7.874 g/cm3 for iron (Fe), calculate the atomic density and atomic radius in the metals if Ti occupies 74% of the volume and Fe occupies 68% of the volume.
Solution:Calculate Volume per Atom in
the Solid: densityatomic/solidinatomperVolume 1
atom/cm.cm/atoms. 323322 10431109961 /:Ti
atom/cm.cm/atoms. 323322 1017811049181 /:Fe
Calculate Atomic Volume:
atombyoccupiedfractionatompervolumevolumeAtomic
atom/cmx..atom/cm. 323323 1006174010431 :Ti
atom/cmx..atom/cm. 324323 10018680101781 :Fe
Periodic Table Chemical Trends
9.) Example: converting mass density to molar and atomic densityGiven a density of 5.54 g/cm3 for titanium (Ti) and a density of 7.874 g/cm3 for iron (Fe), calculate the atomic density and atomic radius in the metals if Ti occupies 74% of the volume and Fe occupies 68% of the volume.
Solution:Calculate Atomic Radius:
34
3
volumeatomic
radiusAtomic
3
3
4rspherevolume
pmcm.cm.
: 136103614
100613 83323
Ti
pmcm.cm.
:e 124102414
100183 83324
F
200 pm
172 pm
Smaller than atomic radius because of interatomic interactions
Periodic Table Trends in Physical Properties
1.) Classification of the Elements Elements in Periodic table are classified into three broad
categories
Metals
Nonmetals
Semimetals
Metallic character associated with few valence s and p electrons and increases as those electrons are located farther from the nucleus
Increasing metal characteristics
Periodic Table Trends in Physical Properties
1.) Classification of the Elements Metals
Vast majority (~75%) of the elements Left-hand of the periodic table Defined by being:
Malleable – pounded into a sheet Ductile – drawn into a wire Most are solid at room temperature Silvery shiny sheen Conduct heat and electricity well Low electronegativity values Low ionization energy
Valence electrons held looselyFacile movement of metal atoms over each other in solid
Periodic Table Trends in Physical Properties
1.) Classification of the Elements Nonmetals
Right-side of the periodic table Defined by being:
Variable physical states Solids are brittle and poor conductors of heat and electricity Insulating solids high electronegativity values
Allotropes: different forms of the same elements with different properties Carbon:
- diamond: hardest material known cutting tool
- graphite: conductor, lubricant but not malleable or ductile
- “bucky balls”
Bucky ball Graphite Diamond
Periodic Table Trends in Physical Properties
1.) Classification of the Elements Semimetals (metalloids)
Smallest number of elements Fall between metals and nonmetals Some properties common to metals others to nonmetals Defined by being:
Solids at room temperature Brittle Poor conductors of electricity
Semiconductors: increasing conductivity with temperature properties Metals conductivity decrease with temperature Silicon (Si) and Germanium (Ge)
Silicon wafer
Periodic Table Trends in Physical Properties
2.) Physical Form of the Elements Phase of the elements at room temperature also reveals a periodic variation.
Most elements are solids, some are gases, few are liquids Except for 1st period every period begins with solid and ends with gas
Different interactions among atoms of the element
solid gas
Periodic Table Trends in Physical Properties
3.) Interactions and the Three Phases of Matter Solids – holds its shape without support of a container
Interactions in solid must be strong Liquids – adopt shape of container
Atoms in liquid flow readily over one another Interactions are weaker than in a solid
Gas – expands to fill container Interactions are very weak
Periodic Table Trends in Physical Properties
4.) Phase Transitions: transforming from a solid to a liquid and from a liquid to a gas
Solid Liquid Gas
Decreasing temperature Increasing temperature
Melting point
Freezing point
Boiling point
Condensation point
Increasing energyDecreasing energy
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