Unit One Chemistry – Horsham College

Chapter 4 – VCE Chemistry

The Modern Periodic Table

Periodic Table Development• No chemistry textbook, classroom, lecture

theatre or research laboratory is complete without a copy of the periodic table of the elements.

• Chemists attempted to arrange the known elements in ways that revealed similarities between them.

• However, it required the genius of Mendeleev to see that arranging elements into patterns was not enough;

• He realised that there was a natural plan in which each element has its allotted place, and this applies not only to the known elements but to some that were still undiscovered.

• Today there are 111 elements recognised by IUPAC, and these are usually displayed in the form of a matrix called a periodic table.

What Patterns?• Before the 1800’s, scientists and

alchemists did not consider the idea of patterns occurring between the known elements.

• Elements were considered unique and unrelated to any other element.

• Scientists who suggested that patterns may exist were ridiculed.

• Sodium and Potassium were discovered in the early 1800’s. Both have very similar properties.

• Empirical evidence later suggested that elements could be sorted in order of increasing atomic weight

• Elements were found to have repeating patterns. This is known as the periodic law.

• The advancing knowledge of the atomic model furthered chemists knowledge of elemental properties.

Early classification -Antoine Lavoisier of 1789

• Antoine Lavoisier's 1789 classification of substances divided substances into four 'element' groups.

• The list contained substances that could not be broken down further.

1. Acid-making elements; Sulphur, Phosphorus, charcoal 2. gas-like elements; Light, caloric (heat), oxygen 3. metallic elements; cobalt, mercury, tin, copper, nickel, iron,

gold, lead, silver, zinc, manganese, tungsten, platinum4. earthy elements; lime, magnesia, barytes, azote, argilla, silex

Lavoisier also formed the basis for the modern list of elements.

Döbereiner’s Triads• In 1829, German Johann Döbereiner

discovered that groups of elements with similar chemical properties such as Lithium, Sodium and Potassium had a strange similarity.

• The average of the atomic weight of Lithium and Potassium was the same as the atomic weight of Sodium.

• The middle element in the triad had properties halfway between the properties of the other two.

• This pattern was replicated with Calcium, Strontium and Barium as well as Sulphur, Selenium, and Tellurium and also Chlorine, Bromine and Iodine.

• In addition, the densities of some of the triads followed the same relationship.

• These groups became known as "Döbereiner's triads".

Ca   Sr   Ba     (40 + 137) ÷ 2 = 88 40   88   137

The Cylinder of Elements• In 1862, Frenchman

Alexandre de Chancourtois published a cylindrical arrangement of the elements (Also called the telluric screw).

• The elements, based on Oxygen-16, differed by 16 in their atomic weight.

• Like Döbereiner, Chancourtois’ cylinder received little attention.

The Law of Octaves• English Chemist, John Newlands

discovered that every eighth element had similar properties.

• He called this the law of octaves (Analogy with music).

• Newlands developed a table in which he placed elements with similar properties in the same collum.

• Unfortunately, his table was ridiculed by the Royal Society in 1864.

However, while successful for some elements, Newlands' law of octaves failed for two reasons:

1. It was not valid for elements that had atomic masses higher than Ca.

2. When further elements were discovered, such as the noble gases (He, Ne, Ar), they could not be accommodated in his table.

John Newlands

Questions 4.1

• Complete questions 1-4 on P. 72 of Nelson VCE Chemistry.

Mendeleev and Meyer

• Russian Dmitri Mendeleev and German Julius von Meyer went on to independently develop their versions of the periodic law.

• Both chemists produced remarkably similar results at the same time working independently of one another.

• Therefore, there has been some disagreement about who deserves credit for being the "father" of the periodic table

Dmitri Mendeleev• In 1869 Mendeleev arranged elements

by atomic weights and properties.• Mendeleev's periodic table of 1869

contained 17 columns with two partial periods of seven elements each (Li-F & Na-Cl) followed by two nearly complete periods (K-Br & Rb-I).

• In 1871 Mendeleev revised the 17-group table with eight columns (the eighth group consisted of transition elements).

• This table exhibited similarities not only in small units such as the triads, but showed similarities in an entire network of vertical, horizontal, and diagonal relationships.

• The table contained gaps but Mendeleev predicted the discovery of new elements. 

• In 1906, Mendeleev came within one vote of receiving the Nobel Prize in chemistry.

Julius von Meyer• Julius von Meyer also developed

a periodic table based on atomic masses, independently of Mendeleev.

• However, Meyer presented only 28 elements.

• Meyer had several inaccuracies and some elements were not included.

• Meyer was the first scientist to introduce the concept of valence as a periodic property.

• Also, Meyer never came to the idea of predicting new elements and correcting atomic weights.

• Only a few months after Mendeleev published his periodic table of all known elements (and predicted several new elements to complete the table, plus some corrected atomic weights), Meyer published a virtually identical table.

Questions 4.2

• Complete questions 1-5 on P. 75 of Nelson VCE Chemistry.

Henry Moseley• Using atomic number instead of

atomic mass as the organising principle was first proposed by the British chemist Henry Moseley in 1913.

• Before this discovery, atomic numbers were just sequential numbers based on an element's atomic weight.

• Moseley's discovery showed that atomic numbers had an experimentally measurable basis.

• Atomic number solved anomalies like Iodine, that has a higher atomic number than tellurium - so, even though he didn't know why, Mendeleev was right to place it after tellurium after all!

• Moseley's research also showed that there were gaps in his table at atomic numbers 43 and 61 which are now known to be radioactive and not naturally occurring.

• Following in the footsteps of Dmitri Mendeleyev, Henry Moseley also predicted new elements.

Glenn Seaborg• In the 1930s, the heaviest elements were

being put up in the body of the periodic table• Glenn Seaborg "plucked those out" while

working with Fermi in Chicago, naming them the Actinide series.

• This later permitted proper placement of subsequently 'created' elements - the Transactinides, changing the periodic table yet again.

• These elements were shown separate from the main body of the table.

• The concept demonstrated how the heavy elements fit into the Periodic Table and thus demonstrated their relationships to the other elements.

• In addition to the discovery of transuranium elements,  Seaborg and his colleagues are responsible for the identification of more than 100 isotopes of elements throughout the Periodic Table.

The Periods of the Periodic Table

• The horizontal rows of the table are called periods.

• There are 7 periods.• Elements in the same

period have the same outermost occupied shell.

Example – Period 2 is filling the second shell.

The Groups of the Periodic Table

• The vertical columns are called groups.• Groups are numbered 1-18. This replaces the old

system of I-VIII.• Groups families have the same number of valence

electrons in their valence (outermost) shell.

The periodic table groups are as follows (in the brackets are shown the old systems: European and American):

• Group 1 (IA,IA): the alkali metals or hydrogen family/lithium family • Group 2 (IIA,IIA): the alkaline earth metals or helium family/beryllium

family • Group 3 (IIIA,IIIB): the scandium family • Group 4 (IVA,IVB): the titanium family • Group 5 (VA,VB): the vanadium family • Group 6 (VIA,VIB): the chromium family • Group 7 (VIIA,VIIB): the manganese family • Group 8 (VIII): the iron family • Group 9 (VIII): the cobalt family • Group 10 (VIII): the nickel family • Group 11 (IB,IB): the coinage metals (not an IUPAC-recommended name)

or copper family • Group 12 (IIB,IIB): the zinc family • Group 13 (IIIB,IIIA): the boron family • Group 14 (IVB,IVA): the carbon family • Group 15 (VB,VA): the pnictogens (not an IUPAC-recommended name) or

nitrogen family • Group 16 (VIB,VIA): the chalcogens or oxygen family • Group 17 (VIIB,VIIA): the halogens or fluorine family • Group 18 (Group 0): the noble gases or helium family/neon family

Questions 4.3

• Complete questions 1-5 on P. 80 of Nelson VCE Chemistry.

The Blocks of the Periodic Table (s-block)

The s-block• The s subshell of the valence shell is

being filled.• Since a s subshell holds 2 electrons,

only 2 groups of elements (Groups 1 & 2) are in this block

Facts• In the outermost occupied shell there

are 1 or 2 electrons in the s subshell but none in the p subshell.

• If the second outermost shell contains a d subshell, it does not contain electrons.

The Blocks of the Periodic Table (p-block)

The p-block• The p subshell of the outermost

shell is being filled.• A p subshell can hold only 6

electrons, hence there are 6 groups in the p-block

Facts• In the outermost occupied shell

there are 2 electrons in the s subshell and 1 or more electrons in the p subshell.

• If the second outermost shell contains a d subshell, it is full.

The Blocks of the Periodic Table (d-block)

• The d subshell is being filled.• Due to the order of of energies of the subshells, this only occurs after the next shell

has started to fill.• A d subshell can hold 10 electrons, hence 10 groups are found in the d-block.• Metals in this block are collectively known as the transition metals.• 3d subshell filling elements are called first transition series. 4d are second etc.Electron configuration;• In the outermost occupied shell the s subshell is full but there are no electons in the

p subshell.• The d subshell of the second outermost shell contain 1 or more electrons

Questions 4.4

• Complete questions 1-5 on P. 83 of Nelson VCE Chemistry.

The Noble Gases• The noble gases are found in group 18 of the modern periodic table. They were not

included in the original periodic table.• Noble gases are found in minerals or in the atmosphere in trace amounts.• Noble gases are un-reactive (inert) due to having a full outer shell. • Henry Cavendish, in 1784, placed some air and pure oxygen into a U-shaped tube that

contained mercury.• He then added some salts and a base to the mercury. Cavendish used a electric

discharge to start the reaction.• These reactions removed the nitrogen and oxygen from the air.• Surprisingly a bubble remained in the top of the tube.• This unreactive bubble was called ‘Cavendish’s bubble’.• More than 100 years, this bubble was named Argon meaning Greek for ‘lazy one’.

Rayleigh and Ramsey• In the late nineteenth century, Lord

Rayleigh and William Ramsay theorised that the nitrogen extracted from air was associated with another gas, argon.

• With this discovery, they realized that a whole class of gases was missing from the periodic table.

• Eventually all the known noble gases except for helium were discovered in the air, with argon being much more common than the others, and the table was completed.

• Helium was detected spectrographically in the Sun in 1868. The isolation of helium on Earth had to wait until 1895.

• Radon was isolated and studied in 1910 after many years of investigating by Ramsey. Radon is radioactive.

Elements known before 1700:

Elements known before 1700, plus those discovered between 1700 and 1799:

Elements known before 1800, plus those discovered between 1800 and 1899:

Elements known before 1900, plus those discovered between 1900 and 2005:

The Missing Elements

• By 1925, 88 out of the 92 naturally occurring elements had been identified.

• Elements 43 (Technetium) ,61 (Promethium), 85 (Astatine) and 87 (Francium) were missing.

• All are radioactive with very short half-lives.• 61,85 and 87 have been identified in decaying uranium. All are

extremely rare.• 43 has only been produced synthetically.• The periodic table is now complete!

Alternative Tables The periodic spiral of Professor Thoedor Benfey.

Alternative Tables Albert Tarantola’s orbital periodic table.

Alternative Tables Alexander Arrangement of the Elements

Stowe’s Arrangement

Questions 4.5

• Complete questions 1-4 on P. 86 of Nelson VCE Chemistry.

Review Questions

• Complete questions 1-8 on P. 88-89 of Nelson VCE Chemistry.