Chapter 5Chapter 5

The Periodic LawThe Periodic Law

Modern Russian TableModern Russian Table

Chinese Periodic TableChinese Periodic Table

Orbital Filling TableOrbital Filling Table

Periodic Table with Group NamesPeriodic Table with Group Names

Chapter 5Chapter 5

The Periodic LawThe Periodic Law

5.1 History of the Periodic Table

Predecessors to the Modern Periodic Predecessors to the Modern Periodic TableTable

• Dobereiner’s Triads

J.W. Dobereiner classified some elements into groups of three, which he called triads.

• similar chemical propertiessimilar chemical properties

• physical properties varied in an orderly physical properties varied in an orderly way according to their atomic masses.way according to their atomic masses.

Mendeleev’s Periodic TableMendeleev’s Periodic Table

Dmitri MendeleevDmitri Mendeleev

Predecessors to the Modern Periodic Predecessors to the Modern Periodic TableTable

• Mendeleev’s Periodic Table

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

• PeriodicityPeriodicity is the tendency to recur at regular intervals.

Mendeleev’s TableMendeleev’s Table

"The chemical properties of the elements are a periodic function of

their atomic weights"

Mendeleev's Periodic TableMendeleev's Periodic Table

• Mendeleev made some exceptions to

place elements in rows with similar

properties (telluriumtellurium & iodine'siodine's places were switched)• Missing ElementsMissing Elements: gaps existed in Mendeleev’s table• Mendeleev predicted the properties of the “yet to be

discovered” elements

(scandium, germanium and gallium)

VerticalVertical column

s in atomic weight order

HorizontalHorizontal rows have similar chemical properties

Problems with Mendeleev’s TableProblems with Mendeleev’s Table

Moseley helped to clarify some of the problems…

Why didn't some Why didn't some elements fit in order of elements fit in order of

increasing atomic increasing atomic mass?mass?

Why did elements exhibit Why did elements exhibit periodic behavior?periodic behavior?

Henry Moseley 1887-1915Henry 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 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 atomThe periodic table was found to be in atomic The periodic table was found to be in atomic

number order, not atomic mass order!!!number order, not atomic mass order!!!• This explained tellurium-iodine anomaly

• ***Moseley was killed in battle in 1915, during WWI. He was 28 years old

The Periodic LawThe Periodic Law The physical and chemical properties of the

elements are periodic functions of their atomic numbers

Discovery of the Noble Gases

1868 1894 1895 1898 1900

Helium discovered as a component of the sun, based on the emission spectrum of sunlight

Freidrich Dorn

discovers radon

William Ramsay

discovers argon

Ramsay finds helium

on Earth

Ramsay discovers krypton

and xenon

Sir William Ramsay

• The LanthanidesThe 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 ActinidesThe 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 5Chapter 5

The Periodic LawThe Periodic Law

5.2 Electron Configuration & The Periodic Table

11 22 33 44 55 66 77 88 99 1010 1111 1212 1313 1414 1515 1616 1717 1818

Sublevel Blocks on Sublevel Blocks on the Periodic Tablethe Periodic Table

Easily lose 1 valence electron (Reducing agents)

React violently with water React with halogens to form salts

The Properties of a Group: the Alkali Metalsthe Alkali 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

The Properties of a Group: the Alkali Earth Metalsthe Alkali Earth Metals

Chapter 5Chapter 5

The Periodic LawThe Periodic Law

5.3 Electron Configuration & Periodic Properties

Half of the distance between nuclei in covalently bonded diatomic molecule

"covalent atomic radii"

Periodic Trends in Atomic Radius:

Radius decreases across a perioddecreases across a period

Increased effective nuclear charge dueto decreased shielding

Radius increases down a groupincreases down a group

Addition of principal quantum levels

Determination of Atomic Radius:

Table of Table of Atomic Atomic

RadiiRadii

How to Achieve an Octet…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 IonizationPredicting Ionization • Metals tend to lose electrons

They form cations.

Ex: Na, 1s22s22p63s1 becomes Na+1,1s22s22p6

• Nonmetals tend to gain electrons.

They form anions.

Ex: O, 1s22s22p4 becomes O-2, 1s22s22p6

Electron Transfer: AnionsElectron 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 + eX + e-- = X = X ––

Ex: Nitrogen Atom + 7 protons

- 7 electrons

Nitrogen Ion +7 protons

- 10 electrons

Neutral

-3 charge

Electron Transfer: CationsElectron 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 X - (e- (e--) = X ) = X ++

Ex: Potassium Atom + 19 protons- 19 electrons

Potassium Ion +19 protons-18 electrons

Neutral

+1 charge

Increases for successive electronsIncreases for successive electrons taken from the same atom Tends to increase across a periodincrease 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 groupdecrease down a groupOuter electrons are farther from the nucleus

Ionization EnergyIonization Energy - the energy required to remove an electron from an atom

Ionization of MagnesiumIonization of Magnesium

Mg + 738 kJ Mg+ + e-

Mg+ + 1451 kJ Mg2+ + e-

Mg2+ + 7733 kJ Mg3+ + e-

Table of 1Table of 1stst Ionization Energies Ionization Energies

Another Way to Look at Ionization Another Way to Look at Ionization EnergyEnergy

Affinity tends to increase across a periodincrease across a period

Affinity tends to decrease down a groupdecrease down a group

Electrons farther from the nucleusexperience less nuclear attraction

Some irregularities due to repulsive forces in the relatively small p orbitals

Electron AffinityElectron Affinity - the energy change associated with the addition of an electron

Table of Electron AffinitiesTable of Electron Affinities

Ionic RadiiIonic RadiiCations

Positively charged ions Smaller than the corresponding

atomAnions

Negatively charged ions

Larger than the corresponding atom

Summation of Periodic TrendsSummation of Periodic Trends

Table of Ion SizesTable of Ion Sizes

ElectronegativityElectronegativity

A measure of the ability of an atom in a chemicalcompound to attract electrons

Electronegativities tend to increase acrossincrease across a perioda period

Electronegativities tend to decrease down adecrease down a group or remain the samegroup or remain the same

Periodic Table of ElectronegativitiesPeriodic Table of Electronegativities