1. HC HC (B) Periodicity History and trends of the periodic table
CHEMISTRY HC
CHEMISTRY
(B) Periodicity
Overview
Overview
History and trends of the periodic table
Covalent radius and Ionisation
Electronegativity
Bonding in the first twenty elements

2. History and trends of the Periodic TableHC
CHEMISTRY HC
CHEMISTRY
(B) Periodicity
History and trends of the Periodic Table
After completing this topic you should be able to :
Learning intention
Learn how the elements are organised into groups and periods in order of increasing atomic number
To identify important classifications of elements within the periodic table.

3. It has taken many years of work by many scientists to find out about the elements that we know about now (and there may be more that we don’t know about yet).

4. Ancient Times - Prior to 1 A.D.
Gold Mercury
Silver Carbon
Copper Sulphur
Iron LeadTin

5. Timeline of the elements
Arsenic (Magnus ~1250)
Antimony (17th century or earlier)
Phosphorus (Brand 1669)
Zinc (13th Century India)
Cobalt (Brandt ~1735)
Platinum (Ulloa 1735)
Nickel (Cronstedt 1751)
Bismuth (Geoffroy 1753)

6. Robert Boyle
In 1661, Robert Boyle showed that there were more than just four elements as the ancients had assumed. Boyle defined an element as a pure substance that cannot be decomposed into any simpler substance.

7. Time line of elements Hydrogen (Cavendish 1766)
Nitrogen (Rutherford 1772)
Oxygen (Priestley; Scheele 1774)
Chlorine (Scheele 1774)
Manganese (Gahn, Scheele, & Bergman 1774)
Molybdenum (Scheele 1778)
Tungsten (J. and F. d'Elhuyar 1783)
Tellurium (von Reichenstein 1782)

8. Lavoisier 1789
The first modern list of chemical elements was given in Antoine Lavoisier's 1789 Elements of Chemistry, which contained thirty-three elements, including light.
Introduced a logical system for naming compounds
and helped introduce the metric system

9. Time of the chemists Uranium (Peligot 1841) Strontium (Davey 1808)
Titanium (Gregor 1791) Yttrium (Gadolin 1794) Vanadium (del Rio 1801) Chromium (Vauquelin 1797) Beryllium (Vauquelin 1798) Niobium (Hatchett 1801) Tantalum (Ekeberg 1802)

10. Atomic Weights
John Dalton, 1803, was the first chemist to use the term ‘atom’
He used this idea to explain how elements react together to
form molecules.
Dalton suggested that it should be possible to compare the
masses of atoms.
Hydrogen 1
Carbone
4.2
Oxygen
5.5
Water
6.5
Sulphur
14.4
Sulphuric Acid
25.4

11. Cerium (Berzelius & Hisinger; Klaproth 1803) Palladium (Wollaston 1803) Rhodium (Wollaston ) Osmium (Tennant 1803) Iridium (Tennant 1803) Sodium (Davy 1807) Potassium (Davy 1807) Barium (Davy 1808) Calcium (Davy 1808) Magnesium (Black 1775; Davy 1808) Boron (Davy; Gay-Lussac & Thenard 1808) Iodine (Courtois 1811) Lithium (Arfvedson 1817) Cadmium (Stromeyer 1817) Selenium (Berzelius 1817) Silicon (Berzelius 1824) Zirconium (Klaproth 1789; Berzelius 1824) Aluminum (Wohler 1827) Bromine (Balard 1826) Thorium (Berzelius 1828) Lanthanum (Mosander 1839) Terbium (Mosander 1843) Erbium (Mosander 1842 or 1843) Ruthenium (Klaus 1844) Cesium (Bunsen & Kirchoff 1860) Rubidium (Bunsen & Kirchoff 1861) Thallium (Crookes 1861) Indium (Riech & Richter 1863

12. Answers to Pre-Lab Questions
1. What is an element? How many different kinds of atom is any element made of?
An element is a substance made of only one kind of atom.
2. What is the atomic mass of an element?
The atomic mass is the mass of an atom of a particular element. It is the total number of protons and neutrons in the nucleus of an atom of a particular element, averaged over all the isotopes of the element. (Note: students may not have studied isotopes yet, and may not be ready to grapple with the distinction between atomic mass and mass number. At this point it is sufficient that they simply understand atomic mass as resulting from the number of protons and neutrons in the nucleus.)
3. What is the atomic number of an element?
The atomic number is the number of protons in the nucleus of an atom of a given element.
4. How many atoms of each element are present in molecules of the following compounds?
HCl 1 hydrogen, 1 chlorine
H2O 2 hydrogens, 1 oxygen
CH4 1 carbon, 4 hydrogens
NH3 1 nitrogen, 3 hydrogens

16. Newlands
Newlands in 1865, placed elements in order of succession of atomic weights noticed a pattern, noticed that the 8th one was a ‘kind of repetition of the 1st.
He called this the ‘Law of Octaves’.
Element
Atomic weights
Atomic Weights
Hydrogen 1
Fluorine 8
Chlorine 15
Lithium 2
Sodium 9
Potassium 16
Beryllium 3
Magnesium 10
Calcium 17
Boron 4
Aluminium 11
Chromium 18
Carbon 5
Silicon 12
Titanium 19
Nitrogen 6
Phosphorus 13
Manganese 20
Oxygen 7
Sulphur 14
Iron 21

17. Lothar Meyer
Meyer in 1869, independently, put forward a similar list of elements.
Meyer plotted graphs of
melting point, boiling point
and atomic volume against
atomic mass.
He found the properties
varied in a regular way i.e. periodically

18. Mendeleev (1869) In 1869 he published ‘Principles of Chemistry’
- proposed the modern Periodic Table.
- elements with similar properties were placed together
- he left gaps for new 'undiscovered' elements.
he predicted properties of undiscovered elements
arranged in order of increasing relative atomic mass
- some elements were out of order therefore modern table is arranged in Atomic Number
elmoscow.ru
Meyer recognised Mendeleev’s work and both where awarded The Davy medal for Chemistry in 1882.

19. The world’s first view of Mendeleev’s Periodic Table
                                                                                                                                                
The world’s first view of Mendeleev’s Periodic Table
– an extract from Zeitschrift fϋr Chemie, 1869.

20. Correct predictions
The greatness of Mendeleev was that not only did he leave spaces for elements that were not yet discovered but he predicted properties of five of these elements and their compounds including gallium which he called eka-aluminium.

21. Eka-aluminium (Ea) Gallium (Ga)
In Paris (1875) Paul Emile Lecoq de Boisbaudran discovered an element he named gallium after the Latin name for France
Eka-aluminium (Ea)
Gallium (Ga)
Atomic weight
About 68
69.72
Density of solid
6.0 g/cm3
5.9 g/cm3
Melting point
low
29.78oC
Valency 3
Method of discovery
Probably from its spectrum
Spectroscopically
Oxide
Formula Ea2O3, density 5.5 g/cm3. Soluble in both acids and alkalis.
Formula Ga2O3, density 5.88 g/cm3. Soluble in both acids and alkalis.

22. Sir William Ramsay
One thing that Mendeleev did not predict was the discovery of a whole new Group of elements, the noble gases, discovered by Scot William Ramsay and co-workers during the last decade of the 19th century.

23. Groups
Periods

24. Groups
- vertical columns.
- elements in a group show specific similarities.
- common names : Alkali Metals, Halogens, Noble Gases.
increasingly metallic down a group, non-metallic up a group.
- outer shell electrons determine the group number.
Periods
- horizontal rows
- two short periods, four long periods.
elements change from metallic to non-metallic across a period.
- number of the shell determines the period.

25. Periodicity
It is the ideas of Meyer and Mendeleev that we will make use of to try and understand the relationships between the first 20 elements.
Periodicity - the occurrence of patterns in the Periodic Table

26. Density - Lothar Meyer Curve

27. Variation of density (g cm-3) with atomic number
Adapted from New Higher Chemistry E Allan J Harris
period 2 (Li - Ne) maximum at boron (B) - group3
period 3 (Na - Ar) maximum at Aluminium (Al)- group 3 Al B Na Li Ne Ar

28. Variation of density (g cm-3) with atomic number
Adapted from New Higher Chemistry E Allan J Harris
In general in any period of the table, density first increases from group 1 to a maximum in the centre of the period, and then decreases again towards group 0
5th
4th
3rd
2nd

29. Variation of density (g cm-3) with atomic number
Adapted from New Higher Chemistry E Allan J Harris
down a group gives an overall increase in density In Ga Al B Cs Rb Na K Li

30. Melting point - Lothar Meyer Curve

31. Variation of melting point with atomic number
Adapted from New Higher Chemistry E Allan J Harris
Determined by the strength of intermolecular bonding, between particles
period 2, peak at carbon
period 3, peak at silicon
In general the forces of attraction (intermolecular bonding) for elements on the left of the table must be stronger, or more extensive than between the particles on the right. Li Na Ar Ne

32. Variation of melting point with atomic number
Adapted from New Higher Chemistry E Allan J Harris
Down group 1 the alkali metals m.pt. decrease there must be a decrease in the force of attraction between the particles Li Na K Rb Cs

33. Variation of melting point with atomic number
Adapted from New Higher Chemistry E Allan J Harris
Down group 7 the halogens m.pt. increases there must be a increase in the force of attraction between the particles I Br Cl F

34. Boiling point - Lothar Meyer Curve

35. Variation of boiling point with atomic number
Adapted from New Higher Chemistry E Allan J Harris
period 2, peak at carbon
period 3, peak at silicon
In general we see the same trend in boiling point across the period Li Na Ne Ar

36. Variation of boiling point with atomic number
Adapted from New Higher Chemistry E Allan J Harris
Down group 1 the alkali metals b.p. decrease once again there must be a decrease in the force of attraction between the particles Li Na K Rb Cs

37. Variation of boiling point with atomic number
Adapted from New Higher Chemistry E Allan J Harris
Down group 7 the halogens b.p. increases once again there must be a increase in the force of attraction between the particles Br I Cl F