(B) PeriodicityOverview Overview

History and trends of the periodic table Covalent radius and Ionisation Electronegativity Bonding in the first twenty elements

After completing this topic you should be able to : (B) Periodicity

History and trends of the Periodic TableLearning intention

Learn how the elements are organised into groups and periods in order of increasing atomic numberTo identify important classifications of elements within the periodic table.

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 dont know about yet).

Ancient Times - Prior to 1 A.D.GoldMercurySilverCarbonCopperSulphurIron LeadTin

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)

Robert BoyleIn 1661, Robert Boyle showedthat there were more than justfour elements as the ancientshad assumed.

Boyle defined an element as apure substance that cannot bedecomposed into any simplersubstance.

Time line of elementsHydrogen (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)

Lavoisier 1789Introduced a logical system for naming compoundsand helped introduce the metric systemhttp://web.bilkent.edu.tr/The first modern list of chemical elements was given in Antoine Lavoisier's 1789 Elements of Chemistry, which contained thirty-three elements, including light.

Time of the chemistsUranium (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)

John Dalton, 1803, was the first chemist to use the term atomHe used this idea to explain how elements react together toform molecules.Dalton suggested that it should be possible to compare the masses of atoms.Atomic Weightswww.bioanalytical.com

Hydrogen1Carbone4.2Oxygen5.5Water6.5Sulphur14.4Sulphuric Acid25.4

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

NewlandsNewlands 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. www.chemsoc.org

ElementAtomic weightsElementAtomic WeightsElementAtomic WeightsHydrogen1Fluorine8Chlorine15Lithium2Sodium9Potassium16Beryllium3Magnesium10Calcium17Boron4Aluminium11Chromium18Carbon5Silicon12Titanium19Nitrogen6Phosphorus13Manganese20Oxygen7Sulphur14Iron21

Lothar MeyerMeyer 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

www.apsidium.com

- 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 Mendeleev (1869)

elmoscow.ruMeyer recognised Mendeleevs work and both where awarded The Davy medal for Chemistry in 1882.In 1869 he published Principles of Chemistry

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.

In Paris (1875) Paul Emile Lecoq de Boisbaudran discovered an element he named gallium after the Latin name for France

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.Sir William Ramsay

PeriodsGroups

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.

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 TablePeriodicity

Density - Lothar Meyer Curve

Variation of density (g cm-3) with atomic numberAdapted from New Higher Chemistry E Allan J Harrisperiod 2 (Li - Ne) maximum at boron (B) - group3period 3 (Na - Ar) maximum at Aluminium (Al)- group 3

Variation of density (g cm-3) with atomic numberAdapted from New Higher Chemistry E Allan J HarrisIn 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 02nd3rd4th5th

Variation of density (g cm-3) with atomic numberAdapted from New Higher Chemistry E Allan J Harrisdown a group gives an overall increase in density

Melting point - Lothar Meyer Curve

Variation of melting point with atomic numberAdapted from New Higher Chemistry E Allan J HarrisDetermined by the strength of intermolecular bonding, between particlesperiod 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.

Variation of melting point with atomic numberAdapted from New Higher Chemistry E Allan J HarrisDown group 1 the alkali metals m.pt. decrease there must be a decrease in the force of attraction between the particles

Variation of melting point with atomic numberAdapted from New Higher Chemistry E Allan J HarrisDown group 7 the halogens m.pt. increases there must be a increase in the force of attraction between the particles

Boiling point - Lothar Meyer Curve

Variation of boiling point with atomic numberAdapted from New Higher Chemistry E Allan J Harrisperiod 2, peak at carbon period 3, peak at silicon In general we see the same trend in boiling point across the period

Variation of boiling point with atomic numberAdapted from New Higher Chemistry E Allan J HarrisDown group 1 the alkali metals b.p. decrease once again there must be a decrease in the force of attraction between the particles

Variation of boiling point with atomic numberAdapted from New Higher Chemistry E Allan J HarrisDown group 7 the halogens b.p. increases once again there must be a increase in the force of attraction between the particles

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