Instructor:

1
NEVER FORGET
Instructor Dr. Robert Powers
Office Address 722 HaH Phone
472-3039 e-mailrpowers3_at_unl.edu web page
http//bionmr-c1.unl.edu
September 11, 2001
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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 and physical properties of
the elements
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Periodic Table
Chemical Trends
1s1
Hydrogen (gas)
Ar3d104s1
Copper (solid)
Xe5d106s2
Mercury (liquid)
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Periodic Table
Chemical Trends 1.) Chemical trends based on the
combination of the electron configuration, octet
rule and electronegativity 2.) Electronegativity
a.) tendency to attract electrons in a
compound b.) empirically based range from 0.7
to 3.98
Attracts electrons
Donate electrons
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Periodic Table
Chemical Trends 1.) Chemical trends based on the
combination of the electron configuration, octet
rule and electronegativity 2.) Electronegativity

High electronegativity pulls electrons away from
elements with weaker electronegativity
Low electronegativity easily loses electrons to
elements with higher electronegativity
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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.
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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 11 ionic compound where Group IA loses e-
  and Group VIIA gains e-
• Ionic compounds are usually solids

high
ns1
ns2p5
low
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Periodic Table

• 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-
pale yellow
dark brown
clear
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
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Periodic Table

• Chemical Trends
• 6.) Example electronegativity difference
  determines chemical products
• Halides 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 chlorin
e 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
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Clicker Question
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Clicker Question What is a main factor that
results in an atom having an increasing 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
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Periodic Table

• Chemical Trends
• 7.) Size of Atom
• Atomic radius radius of the sphere containing
  90 of the electron density for the free atom
  ? related to electronic configuration
• Progressing 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

Increasing Atomic Radius
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Periodic Table

• Chemical Trends
• 7.) Size of Atom
• Progressing 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-orbitals

Decreasing Atomic Radius
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Periodic Table

• Chemical Trends
• 7.) Size of Atom
• Changes in Size Affects Chemical Behavior

Increase in ionization energy electron
affinity electronegativity
Increase in attraction between nucleus and
electrons
Decrease in Radius
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Periodic Table

• Chemical Trends
• 8.) Size of Ion
• When an atom gains or loses an electron, the ion
  is a different size than the neutral atom

Like Charges Repel Remove e- ? remove repulsion
? smaller positive charged ion (cation) is
smaller Add e- ? add repulsion ?
larger negatively charged ion (anion) is larger
Size difference can be dramatic, about a factor
of 2
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Periodic Table

• Chemical Trends
• 8.) Size of Ion
• When 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 charge Again,
greater nuclear charge can hold electrons closer
than smaller nuclear charge 2s22p6 7N3- gt
8O2- gt 9F- gt 11Na gt 12Mg2 gt 13Al3
171 140 133
102 72 50 picometers
(pm)
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Periodic Table

• Chemical Trends
• 9.) Example converting mass density to molar and
  atomic density
• Given 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 Molar Density
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Periodic Table

• Chemical Trends
• 9.) Example converting mass density to molar and
  atomic density
• Given 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
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Periodic Table

• Chemical Trends
• 9.) Example converting mass density to molar and
  atomic density
• Given 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
Calculate Atomic Volume
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Periodic Table

• Chemical Trends
• 9.) Example converting mass density to molar and
  atomic density
• Given 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
Smaller than atomic radius because of interatomic
interactions
200 pm
172 pm
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Periodic Table

• Trends in Physical Properties
• 1.) Classification of the Elements
• Elements in Periodic table are classified into
  three broad categories

Nonmetals
Semimetals
Increasing metal characteristics
Metals
Metallic character associated with few valence s
and p electrons and increases as those electrons
are located farther from the nucleus
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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 loosely Facile movement of
metal atoms over each other in solid
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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

Graphite
Bucky ball
Diamond
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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
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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

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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

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Periodic Table
Trends in Physical Properties 4.) Phase
Transitions transforming from a solid to a
liquid and from a liquid to a gas
Melting point
Boiling point
Gas
Solid
Liquid
Freezing point
Condensation point
Increasing energy
Decreasing energy
Decreasing temperature
Increasing temperature