Transcript Lesson 1 & 2 Periodic table trends and formation

(B) Periodicity
Overview
Overview
• History and trends of the periodic
table
• Covalent radius and Ionisation
• Electronegativity
• Bonding in the first twenty elements
(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.
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).
Ancient Times - Prior to 1
A.D.
Gold
Silver
Copper
Iron
Mercury
Carbon
Sulphur
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 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.
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)
Lavoisier 1789
http://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.
Introduced a logical system for naming compounds
and helped introduce the metric system
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)
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
www.bioanalytical.com
Cerium (Berzelius & Hisinger;
Klaproth 1803)
Palladium (Wollaston 1803)
Rhodium (Wollaston 18031804)
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
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
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’.
www.chemsoc.org
Element
Atomic
weights
Element
Atomic
Weights
Element
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
Manganes
e
20
Oxygen
7
Sulphur
Iron
21
14
Lothar Meyer
www.apsidium.com
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
Mendeleev (1869)
In 1869 he published ‘Principles of Chemistry’
- proposed the modern Periodic Table.
elmoscow.ru
- 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
Meyer recognised Mendeleev’s work and both where
awarded The Davy medal for Chemistry in 1882.
The world’s first view of Mendeleev’s Periodic Table
– an extract from Zeitschrift fϋr Chemie, 1869.
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
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
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.
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
th
co-workers during the last decade of the 19
century.
Groups
Periods
Groups
- vertical columns.
- elements in a group
show specific
similarities.
- common names : Alkali
Metals, Halogens,
Noble Gases.
- increasingly metallic
down a group, nonmetallic up a group.
- outer shell electrons
determine the group
number.
Periods
- horizontal rows
- two short periods, four
long periods.
- elements change from
metallic to nonmetallic across a
period.
- number of the shell
determines the period.
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
Density - Lothar Meyer
Curve
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
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
2nd
3rd
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
Melting point - Lothar Meyer
Curve
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.
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
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
Boiling point - Lothar Meyer
Curve
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
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
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