1. Ch 1: Elements and The Periodic Table

2. Learning Outcomes Symbols of the first 36 elements
History of the idea of elements; contributions from
The Greeks
Boyle
Davy
History of the Periodic Table; contributions from
Dobereiner
Newlands
Mendeleev
Moseley
Comparison of Mendeleev’s table with the modern periodic table

4. Symbols of the Elements
Symbol is usually the first 2 letters of the elements’ name
E.g: Calcium: Ca
Helium: He
BUT not always the English name
E.g: Potassium: K (Kalium)
Lead: Pb (Plumbum)
First letter always a capital, second a letter

5. Symbol Name Symbol Name Symbol Name Symbol Name He Si H P Li S Be ClF Ne Na Mg Al
Symbol
Name Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe
Symbol
Name Co Ni Cu Zn Ga Ge As Se Br Kr
Symbol
Name Hg Pb Rn Ra Ag I Au

6. The History of Idea of Elements
The Greeks
Elements are the basic things of which all others are made
The elements are earth, fire air and water

7. Robert Boyle Born in Ireland
‘Father of Chemistry’
Born in Ireland
Proposed that elements are substances which cannot be broken down into simpler substances
Modern definition:
An element is a substance that cannot be split into simpler substances by chemical means.

8. Humphrey Davy
Discovered many elements by passing electricity through their compounds
e.g. potassium, sodium, magnesium,
calcium
Called electrolysis
Electrolysed water to find that it was made of hydrogen and oxygen in a 2:1 ratio

9. Dobereiner ‘Dobereiner’s triads’
Arranged known elements in triads or groups of 3 which had
Similar chemical properties
The atomic weight of middle element was half way between the other 2
Ideas rejected as not all elements fitted

10. Dobereiner’s Triads: A Triad:Cl
35.5 Ca 40 Li 7 S 32 Br 80 Sr 88 Na 23 Se 79 I
128 Ba
137 K 39 Te
128
A Triad:
A group of 3 elements with similar chemical properties. The atomic weight of the middle element is approximately equal to the average of the other two

11. Unfortunately for Dobereiner, few other cases of triads could be found and his triads were looked on as coincidence that were of little significance.
However, his work was important as it was the earliest attempt to trace a relationship between properties of the elements and their atomic weights.

12. Newlands Newlands Law of Octaves
Arranged elements in order of atomic weight
and noticed that every 8th element was similar
Rejected because it broke down on 3rd octave due to transition elements and undiscovered elements

13. An Octave:
A group of elements arranged in increasing atomic weight so that the 1st and 8th element of each group have similar properties

14. Mendeleev Mendeleev’s Periodic Law
Arranged elements in a Periodic Table according to atomic weight
There were periodic trends in properties
He made this work by
(i) leaving gaps for undiscovered elements
(ii) reversing Te and I
(iii) putting transition elements into subgroups

15. Initially rejected but later accepted when
New elements were discovered which fitted the predicted properties
His reversal of Te and I was justified by the discovery of atomic number

16. Mendeleev’s Periodic Law
When elements are arranged in order of increasing atomic weight (relative atomic mass), the properties of the elements recur periodically, i.e. the properties displayed by an element are repeated at regular intervals in other elements.

17. Mosely
Used X rays to discover the number of protons in each element i.e. atomic number
He found that elements in the Periodic Table are in order of atomic number

18. The Modern Periodic Table
The modern periodic table is an arrangement of increasing atomic number
Atomic Number is the number of protons in the nucleus of the atom
Each element has a different number of protons in their nucleus
When the elements are arranged by increasing atomic number the properties of the elements vary periodically

19. Comparison of Medeleev’s and the Modern Periodic Table
Mendeleev
Modern
Elements arranged in order of increasing atomic weight (r.m.m.)
Elements arranged in order of increasing atomic number
Only 60 elements (rest had not been discovered)
Over 100 elements
Contains gaps for undiscovered elements
No gaps
Transition elements were not put in a separate block
Transition elements are in a separate block

20. Summary of History of Periodic Table
Scientist
Contribution
The Greeks
Robert Boyle
Humphrey Davy

21. Summary of History of Periodic Table
Scientist
Contribution
Dobereiner
Newlands
Moseley

22. Summary of History of Periodic Table
Scientist
Contribution
Mendeleev
Modern Periodic Table

23. The Periodic Table

24. Periodic Groups

25. Group 1- Alkali Metals Properties: Very reactive – stored under oil
Extracted from compounds or ores
Low ionisiation energy and electronegativity value.
Form ionic bonds as tend to loose electrons
Reactivity increase down the group Li Na K Rb Cs
Increasing Reactivity

26. Group 1- Alkali Metals 2K + ½ O2 → K2O
Group 1 react with oxygen to form oxides.
2Li + ½ O2 → Li2O
2Na + ½ O2 → Na2O
2K + ½ O2 → K2O

27. Group 1- Alkali Metals
Group 1 react with water to form hydroxides and hydrogen gas.
Li H2O → LiOH ½H2
Na + H2O → NaOH + ½H2
K H2O → KOH ½H2

28. Group 1 react with HCl to form chlorides and hydrogen gas.
Group 1- Alkali Metals
Group 1 react with HCl to form chlorides and hydrogen gas.
Li + HCl → LiCl ½H2
Na + HCl → NaCl + ½H2
K + HCl → KCl ½H2

29. Alkaline-Earth Metals
Group 2-
Alkaline-Earth Metals Be Mg Ca Sr Ba
Properties:
Metals- harder than the alkali metals
Less reactive than corresponding alkali metals
Reactivity increases down the group
Increasing Reactivity

30. Group 7- Halogens
Highly electronegative and most reactive on Periodic Table
Do not exist free in nature.
F is most reactive than Cl, Br, I, etc.
The reactivity decreases down the group. F Cl Br I At
Increasing Reactivity

31. Group 7- Halogens
Boiling point increase down the group as Van der Waals forces exist between atoms and bigger atoms need more energy to break them apart.

32. Noble Gases Inert gases – do not form compounds
Boiling point increase as you go down the group due to Van der Waal forces exist between atoms and they are stronger between bigger atoms.