Chapter 11
The Periodic Table

I. History of the Periodic Table
• Johann Wolfgang Döbereiner and triads
• John Newlands and the Law of Octaves
• Dmitri Mendeleev and the 1 st periodic table

Mendeleev’s Periodic Table

Mendeleev’s Predictions
Predicted properties for Mendeleev’s Eka-Silicon and properties of Germanium:
Element Atomic Weight Density Oxide formula Chloride formula
Eka-Silicon
(predicted 1871)
72 5.5 g/cm 3 EsO
2
EsCl
4
Germanium
(discovered 1886)
72.59
5.32 g/cm 3 GeO
2
GeCl
4

Periodic Law
• Basis: Element arranged according to their atomic masses present a clear periodicity of properties
• Modern: The properties of elements repeat periodically when the elements are arranged in increasing order by their atomic numbers

Circular Periodic Table

Benfey’s Periodic Table

Physics Periodic Table

ADOMAH periodic table - electron orbitals

Spiral Periodic Table

We like spirals!

Periodic system Pyramid format

Periodic system: Zmaczynski & Bayley

Periodic table in binary electron shells layout, designed by Eric
William McPherson

Regions of the Periodic table

Representative Elements -EC
• Valence v. core electrons

Representative Elements - Ions
• Generalization of atom/ion stability
– Usually means 8 valence = octet rule

Transition Elements - EC
• Remember the exceptions to filling d orbitals

Periodic Trends – Atomic Radii
• Worksheet: Atomic Size
• Why does atomic radius decrease across a period?
– Higher # = more protons = higher core charge
• Increased attraction between p+ & e-
– e- pulled closer to nucleus = ????
• Why does atomic radius increase down a group?
– Valence electron shell  higher n = higher probability
– Shielding by core e- = less pull on valence e- = ????

Atomic Radii

Periodic Trends – Ionic Radii
• Cation (+) radii are smaller than atomic radii
– Why?
• Lose of valence e-
• Results in lower n, resulting in stronger nuclear pull
• Anion (-) radii are larger than atomic radii
– Why?
• Gain of e-
• Results in increased repulsion between e-

Sizes of Anions (- ions)

Sizes of Cations (+ ions)

Graph of Atomic Radii

Definition of Ionization Energy (IE)
• Ionization energy is the energy required to remove an electron from a gaseous atom or ion.
The first or initial ionization energy or E i of an atom or molecule is the energy required to remove one mole of electrons from one mole of isolated gaseous atoms or ions. You may think of ionization energy as a measure of the difficulty of removing electron or the strength by which an electron is bound. The higher the ionization energy, the more difficult it is to remove an electron. Therefore, ionization energy is an indicator of reactivity.

Periodic trends – 1 st Ionization Energy exceptions

Periodic Trends – 2 nd Ionization Energy
B
C
N
O
F
H
He
Li
Be
Ne
Na
Mg
1
1312
2372
520
899
800
1086
1402
1314
1680
2080
496
737
2
5250
7297
1757
2426
2352
2855
3388
3375
3963
4563
1450
3 4 5 6 7 8
11810
14845 21000
3659
4619
25020
6221
32820
37820 47260
4576
5296
6045
7473
7467
8408
9442
10987
11020
53250
13320
15160
64340
71320
17860
84070
92010
6130
6913
7731
9361
9541
12180
13350
15240
16600 20113 25666
10545 13627 17995 21700 25662
*The teal colored cells represent ionization energies where the valence shell is now (n-1). (Why do you think there is such a large jump in the ionization energies when the n-1 shell is now valence?)

Periodic Trends - Electronegativity
• Definition
• Increases across a period (L to R), decreases down a group (top to bottom)

Electronegativity
• Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons.
• The Pauling scale is the most commonly used.
Fluorine (the most electronegative element) is assigned a value of 4.0, and values range down to Cesium and Francium which are the least electronegative at 0.7.

Electron Affinity!

Electron Affinity Definition
• the quantitative measure, usually given in electron-volts (eV), of the tendency of an atom or molecule to capture an electron and to form a negative ion.

Periodic Trend for electron affinity

Periodic Trends - All
*Note: The electron affinity of an element is the energy given off when a neutral atom in the gas phase gains an extra electron to form a negatively charged ion

Wrap-up
• Periodic Table Activity