Chapter 5

The Periodic Law

Modern Russian Table

Chinese Periodic Table

Orbital Filling Table

Periodic Table with Group Names

Chapter 5

The Periodic Law

5.1 History of the Periodic Table

Predecessors to the Modern Periodic Table

•

Dobereiner’s Triads

J.W. Dobereiner classified some elements into groups of three, which he called triads. • similar chemical properties • physical properties varied in an orderly way according to their atomic masses.

Mendeleev’s Periodic Table

Dmitri Mendeleev

•

Predecessors to the Modern Periodic Table

Mendeleev’s Periodic Table

Dmitri Mendeleev realized that the chemical and physical properties of the elements repeated in an orderly way when he organized the elements according to increasing atomic mass .

• In 1869, Mendeleev published a table of the elements organized by increasing atomic mass.

• • Mendeleev was a Russian scientist and is often referred to as the “Father” of the Periodic Table.

Periodicity

intervals.

is the tendency to recur at regular

Mendeleev’s Table

"

The chemical properties of the elements are a periodic function of their atomic weights

"

Mendeleev's Periodic Table

Horizontal rows have similar chemical properties • Mendeleev made some exceptions to Vertical column s in atomic weight order place elements in rows with similar properties ( tellurium & iodine's places were switched) • Missing Elements : gaps existed in Mendeleev’s table • Mendeleev predicted the properties of the “yet to be discovered” elements (scandium, germanium and gallium)

Problems with Mendeleev’s Table

Why didn't some elements fit in order of increasing atomic mass?

Why did elements exhibit periodic behavior?

Moseley helped to clarify some of the problems…

Henry Moseley 1887-1915

• English physicist who determined the number of positive charges in the nucleus (protons) by measuring the wavelength of the x-rays given off by certain metals in 1913. • He was killed by a sniper in Turkey in August 1915 during WWI. Many people think that Britain lost a future Nobel Prize winner. This is because Nobel Prizes, the most prestigious awards for scientific achievement are awarded only to living people.

Moseley and the Periodic Table

•

Protons and Atomic Number

: X-ray experiments revealed a way to determine the number of protons in the nucleus of an atom

The periodic table was found to be in atomic number order, not atomic mass order!!!

• This explained tellurium-iodine anomaly The Periodic Law The physical and chemical properties of the elements are periodic functions of their atomic numbers • ***Moseley was killed in battle in 1915, during WWI. He was 28 years old

Discovery of the Noble Gases

Helium discovered as a component of the sun, based on the emission spectrum of sunlight William Ramsay discovers argon Ramsay finds helium on Earth Ramsay discovers krypton and xenon Freidrich Dorn discovers radon 1868 1894 1895 1898 1900 Sir William Ramsay

• The Lanthanides Early 1900's the elements from cerium (#58) to lutetium (#71) are separated and identified. Also known as the rare earth elements, less than 0.01% naturally occurring. • The Actinides Discovery (or synthesis) of thorium, # 90 to lawrencium #103 • • Both groups pulled out of the table for space reasons.

Periodicity:

Elements with similar properties are found at regular intervals within the "periodic" table

Chapter 5

The Periodic Law

5.2 Electron Configuration & The Periodic Table

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Sublevel Blocks on the Periodic Table

The Properties of a Group: the Alkali Metals Easily lose 1 valence electron (Reducing agents) React violently with water React with halogens to form salts

The Properties of a Group: the Alkali Earth Metals Easily loses 2 valence electron (Reducing agents) Harder, denser, stronger than Group 1 metals Higher melting points Less reactive than Group 1, but too reactive to be found free in nature

Chapter 5

The Periodic Law

5.3 Electron Configuration & Periodic Properties

Determination of Atomic Radius: Half of the distance between nuclei in covalently bonded diatomic molecule "covalent atomic radii" Periodic Trends in Atomic Radius: Radius decreases across a period Increased effective nuclear charge due to decreased shielding Radius increases down a group Addition of principal quantum levels

Table of Atomic Radii

How to Achieve an Octet…

• Atoms can form ions by gaining or losing electrons to obtain a stable outer configuration • Cation- Positive ion (+) ion • Anion- Negative ion (-) ion • Ions attract (opposites attract)

Predicting Ionization

• Metals tend to lose electrons They form cations.

Ex: Na, 1s 2 2s 2 2p 6 3s 1 becomes Na +1 ,1s 2 2s 2 2p 6 • Nonmetals tend to gain electrons.

They form anions.

Ex: O, 1s 2 2s 2 2p 4 becomes O -2 , 1s 2 2s 2 2p 6

Electron Transfer: Anions

• When an atom gains electrons it increases its negative charge so it becomes negatively charged. There are now more electrons than protons.

X + e = X – Ex: Nitrogen Atom + 7 protons - 7 electrons Neutral Nitrogen Ion +7 protons - 10 electrons 3 charge

Electron Transfer: Cations

• When an atom loses electrons, it loses negative charges so it becomes more positively charged. There are now more protons than electrons.

X - (e ) = X + Ex: Potassium Atom Potassium Ion + 19 protons - 19 electrons +19 protons -18 electrons Neutral + 1 charge

Ionization Energy - the energy required to remove an electron from an atom Increases for successive electrons taken from the same atom Tends to increase across a period Electrons in the same quantum level do not shield as effectively as electrons in inner levels Irregularities at half filled and filled sublevels due to extra repulsion of electrons paired in orbitals, making them easier to remove Tends to decrease down a group Outer electrons are farther from the nucleus

Ionization of Magnesium Mg + 738 kJ



Mg + Mg + + 1451 kJ



Mg + e 2+ + e Mg 2+ + 7733 kJ



Mg 3+ + e -

Table of 1 st Ionization Energies

Another Way to Look at Ionization Energy

Electron Affinity - the energy change associated with the addition of an electron Affinity tends to increase across a period Affinity tends to decrease down a group Electrons farther from the nucleus experience less nuclear attraction Some irregularities due to repulsive forces in the relatively small p orbitals

Table of Electron Affinities

Ionic Radii

Cations Positively charged ions Smaller than the corresponding atom Anions Negatively charged ions Larger than the corresponding atom

Summation of Periodic Trends

Table of Ion Sizes

Electronegativity

A measure of the ability of an atom in a chemical compound to attract electrons Electronegativities tend to increase across a period Electronegativities tend to decrease down a group or remain the same

Periodic Table of Electronegativities