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 Decreases Increases

• Atomic Radii are measured using:– rcov which measures from the nuclei

– rvdw van der Waals which is used for non-bonding 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 e-

from 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

• E A Increases

D

e

c

r

e

a

s

e

s

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* / rcov

2 ) + .744

4. Allen EN Scale • EN = nsEs + npEp

ns + np

• 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

• E N Increases

D

e

c

r

e

a

s

e

s

The End. . .