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 1st 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/cm3 EsO2 EsCl4  

Germanium(discovered 1886)

72.59 5.32 g/cm3 GeO2 GeCl4  

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

of finding e- further from nucleus = ????– Shielding by core e- = less pull on valence e- = ????

Smaller radius

Larger radius

Larger radius

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 Ei 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 – 1st Ionization Energy

exceptions

Periodic Trends – 2nd Ionization Energy

  1 2 3 4 5 6 7 8H 1312              He 2372 5250            Li 520 7297 11810          Be 899 1757 14845 21000        B 800 2426 3659 25020 32820      C 1086 2352 4619 6221 37820 47260    N 1402 2855 4576 7473 9442 53250 64340  O 1314 3388 5296 7467 10987 13320 71320 84070F 1680 3375 6045 8408 11020 15160 17860 92010Ne 2080 3963 6130 9361 12180 15240    Na 496 4563 6913 9541 13350 16600 20113 25666Mg 737 1450 7731 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