Transcript Periodic Table and Trends

Review of the
Periodic Table and its Trends
You must be able to read the table!
I
II
III IV V VI VII VIII
The Periods and Valence Orbitals
• The Groups with a Roman Numeral
represent the Primary or A elements
• The others are the Transition Elements
or B elements
• The Lathinides and Actinides are the
Inner Transition Elements
• The Roman Numeral equals the
Number of Valence e- for that Group
• Valence e- are those in the last Energy
level (n)
Dmitri Mendeleev is given credit for developing the first
periodic table based on atomic weight – it allowed him to
predict new elements.
However, it was Henry Moseley who set it
up using the atomic number (Z).
The First Periodic Trend
• Atomic Radius: This varies according to
the distance of the valence e- to the
nucleus
• Two factors affect atomic radius – the
valence shell’s n (energy level) and the
attractions/repulsions that occur in the
atom
• Atomic Radius (and Ionic Radius) is measured in
Angstroms or pm or nm
1 A = 10-10 m = 0.1 nm = 100 pm
Atomic Radius
I
n
c
r
e
a
s
e
s
Decreases
• Atomic Radii are measured using:
– rcov which measures from the nuclei
– rvdw van der Waals which is used for nonbonding noble (inert) gases
• See the charts handed out for actual radii
Metal molecules form lattice
structures – cube shaped crystals
with an atom at each corner.
2. Ionic Radius
• This measures the size of an ion in a
crystal lattice structure
• rion increases if a negative ion (anion)
and decreases with a positive ion
(cation)
This is easy to explain – a cation has lost
e- and an anion has gained them –
changing the radius
3. Ionization Energy (EI)
• This is the energy needed to remove an efrom an atom and create a cation
– The 1st Ionization Energy is the lowest since it
is removing an e- from the valence shell
– EI increases as you get closer to the nucleus
due to an increase in the attraction (EMF)
– Measured in eV or KJ/mol
• 1 eV is the charge of one e• 1 eV = 1.60217653 x 10-19 J = 96.48538 KJ/mol
• EI Increases
D
e
c
r
e
a
s
e
s
• EI decreases due to distance from the
nucleus and due to the shielding or
screening effect
• The Shielding Effect is due to the
interference of inner e-’s disrupting the
forces of nuclear attraction on an outer e– This effect, the Z* or Zeff measures the
amount of nuclear attraction on any
particular electron
• Z* = Z - s
4. Electron Affinity (EA)
• EA is the measure of how capable an atom is
in gaining an e- and becoming an anion
(negative ion)
• When an e- is gained, a quanta of energy is
released as a photon or gamma particle
• This trend really centers on Group VI and VII
• Only Group VI has a 2nd EA
• Measured in – kJ/mol or - eV
• EA
D
e
c
r
e
a
s
e
s
Increases
5. Electronegativity (χ) or (EN)
This is the power of an atom to attract e- and thus,
form bonds
There are several scales used to determine
EN
1. The Pauling Scale ranges from 0.7 to 4.0
The difference in EN between two atoms will
determine what type of bond has been
formed (see the scale handed out in class)
•
•
•
•
2. The Mullikan Scale
Also called the Absolute EN Scale
Uses the mean of the 1st EI and EA to
measure bond attraction
EN in eV = 0.187 (EI + EA / 2) + 0.17
EN in kJ./mol = (1.97 x 10-3)(Mean) + 0.19
3. Allred-Rochow EN Scale
• EN is related to charge experienced on surface
of atom
• Uses Slater’s Rules to find Z*
• EN = 0.359 (Z* / rcov2 ) + .744
•
•
•
•
•
4. Allen EN Scale
EN = nsEs + npEp
ns + n p
Es and Ep are an e- energies of the s and p
orbitals in the valence shell
Ns and np are the number of e- in these orbitals
kJ/mol = _____ x (1.75 x 10-3)
eV = _____ x (0.169)
EN Using the Pauling Scale
• EN
D
e
c
r
e
a
s
e
s
Increases
The End. . .