NEVER FORGET
Instructor:
Dr. Robert Powers
Office
Address: 722 HaH
Phone:
472-3039
e-mail:rpowers3@unl.edu
web page: http://bionmr-c1.unl.edu
September 11, 2001
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
Periodic Table
Chemical Trends
1s1
Hydrogen (gas)
[Ar]3d104s1
Copper (solid)
[Xe]5d106s2
Mercury (liquid)
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
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
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
high
ns1
low
ns2p5
Periodic Table
Chemical Trends
5.) Electronegativity differences determine the outcome of a chemical
reaction


Halogen ions have an
octet in valence shell
No need to share e-
Electronegativity of Chlorine is 3.16
Electronegativity of Bromine is 2.96
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 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
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
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 Atom
Increasing Atomic Radius
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
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
Periodic Table
Chemical Trends
7.) Size of Atom
Changes in Size Affects Chemical Behavior
Decrease in Radius
Increase in attraction
between nucleus and
electrons
Increase in:
ionization energy
electron affinity
electronegativity
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
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:
7N
3-
171
> 8O2- > 9F- > 11Na+ > 12Mg2+ > 13Al3+
140
133
102
72
50
picometers (pm)
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:
mass density g / cm3
Molar density  moles / volume 

 mol / cm3
atomic mass g / mol
Ti : atomic mass  47.867 g / mol
5.54 g / cm3
molar density 
 0.116 mol / cm3
47.867 g / mol
Fe : atomic mass  55.845 g / mol
7.874 g / cm3
molar density 
 0.116 mol / cm3
55.845 g / mol
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:
mass density
g / cm3 atoms
Atomic density  atoms / volume 
 atoms / mole 
x
 atoms / cm3
atomic mass
g / mol
mol
Ti : 0 .116 mol / cm 3 6.022137 x10 23 atoms / mol  6.99  10 22 atoms / cm 3
Fe : 0 .1410 mol / cm 3 6.022137 x10 23 atoms / mol  8.491  10 22 atoms / cm 3
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:
Volume per atom in solid  1 / atomic density
Ti : 1/6.99  10 22 atoms / cm 3  1.43  10 23 cm 3 / atom
Fe : 1/8 .491  10 22 atoms / cm 3  1.178  10 23 cm 3 / atom
Calculate Atomic Volume:
Atomic volume  volume per atom    fraction occupied by atom 
Ti : 1.43  10 23 cm 3 / atom  0.74  1.06 x10 23 cm 3 / atom
Fe : 1.178  10 23 cm 3 / atom  0.68  8.01 x10 24 cm 3 / atom
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:
volume sphere 
4 3
r
3
Atomic radius  3
3  atomic volume
4
Smaller than atomic
radius because of
interatomic interactions
23
3
3

1
.
06

10
cm
Ti : 3
 1.36  10 8 cm  136 pm
4
200 pm
24
3
3

8
.
01

10
cm
Fe : 3
 1.24  10 8 cm  124 pm
4
172 pm
Periodic Table
Trends in Physical Properties
1.) Classification of the Elements

Nonmetals
Elements in Periodic table are classified into three broad
categories
Semimetals
Metals
Metallic character associated with few valence s and p electrons and
increases as those electrons are located farther from the nucleus
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
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

Bucky ball
Carbon:
- diamond: hardest material known  cutting tool
- graphite: conductor, lubricant but not malleable or ductile
- “bucky balls”
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
Melting point
Boiling point
Gas
Liquid
Solid
Freezing point
Decreasing energy
Decreasing temperature
Condensation point
Increasing energy
Increasing temperature