1. Elements and Periodic Table of Elements
Chemistry
Elements and
Periodic Table of Elements

2. The Basics Element = all the atoms are the same (JC)
Element – cannot be broken down chemically into simpler substances
(nuclear reactions are a different story!)
How do we know what’s an element?

3. Periodic Table of ……
Elements
Need to know
symbols of elements 1- 36

4. learn the rest as we go through the course
is for Carbon
but
watch out for ………
Potassium is K
Phosphorus is P
learn the rest as we go through the course

5. Be careful
Symbol
can only have one capital letter Na
not NA

6. History Greeks – 4 elements – were they right? Boyle
(2000 ish years later!)
better idea of element
can’t be broken down into simpler substance

7. Davy
used electricity to break down compounds into their elements
(JC – you saw water broken into H and O)
he isolated Na, K, Ba, Sr, Ca, Mg

8. Moseley used x-rays showed that the nucleus had positive charge
each element had different positive charge on its nucleus
Element …….
all elements have the same atomic number (no. of protons

9. Same number of electrons in outside shell
Periodic Table
Same number of electrons in outside shell
Vertical Lines are called
Groups
Horizontal Lines are called
Periods
Metals on left , non- metals in right
division begins at Boron
(check with Aluminium Al)
Same number of shells

10. Learning Check Do I know…. (LC) definition of an element?
4 steps in how idea of element developed?
Where is a group on PTE?
What a group tells you?
Where is a period on PTE?
What this tells you?
Correct way to write the symbols ?

11. Periodic Table History

12. Dobereiner He put elements with similar chemical properties together
They went into in groups of 3
He noticed these trends in groups of elements such as:
Atomic Weight of “middle” element is average of other two – approx.
Can you name these elements ?

13. Dobereiner’s Law of Triads
A triad is a group of three elements
with similar chemical properties in which
the atomic mass of the middle element is approximately equal to the average of the other two.
Only worked for very few elements of the 50 or so that were known at the time
BUT
He was first to make a link between atomic weight and properties

15. John Newland
Arranged the 60 known elements in order of increasing atomic weight
His pattern was…
Every 8th element was a repeat
(i.e. had 7 groups)
His Law was called…

16. Law of Octaves
An octave is a group of elements arranged in order of increasing atomic weight, in which the first and the eighth element of each group have similar properties.
The properties repeat every 8 as noble gases hadn’t been discovered yet!
Only worked for 17 out of 60 elements
There were several problems such as iron being grouped with oxygen and sulphur.
Laughed at but was basically correct

17. Mendeleev
Arranged the known elements in order of increasing atomic weight
His Law was called…

18. Mendeleev’s Periodic Law:
When elements are arranged in order of increasing atomic weight (relative atomic mass), the properties of the elements vary periodically.

19. Mendeleev:
Put elements with the same properties in the same vertical group.
Reversed the order of some elements (Te/I) so that their properties matched their group.
Left gaps to make the elements fit into the proper column (group).
Predicted that elements (eg. Germanium and Gallium) would be discovered to fill these gaps. Predicted their properties correctly.

20. Mendeleev’s Modern Periodic Table V Periodic Table
Gaps left for undiscovered elements
Group 0 elements missing
Elements discovered since 1869 missing
D-block elements arranged as subgroups beside each main group
Elements arranged in order of increasing atomic weight in almost all cases.
Gaps have been filled
Group 0 elements included
Elements discovered since 1869 included
D-block elements arranged as subgroups in a separate block
Elements arranged in order of increasing atomic number

21. Mendeleev’s table

22. Moseley – Atomic Number
The atomic number of an atom is the number of protons in the nucleus of that atom.
Moseley used x-rays to find out how much positive charge each nucleus had
In other words the difference between the elements is the number of protons in the nucleus.
Once the atomic number was known it was seen that Mendeleev’s table was in order of increasing atomic number – not weight.

23. Modern Periodic Table In order of increasing atomic number.
There were 63 elements in Mendeleev’s table – now 109
No gaps
The transition elements are listed separately.
Today’s table 1940 – Glenn Seaborg

24. Do I know it??? Who proposed Law of Triads?
Who proposed Law of Octaves?
Who proposed Periodic Law?
Can I explain each ?
Can I name 3 triads?
What was Moseley’s contribution to the Periodic Table development?
Four differences between Mendeleev’s Table and modern table?

25. Alkali metals Group 1 Form +1 ions Very reactive Low density
Soft-can be cut with a knife
Burn in air to form oxides
React with water to form hydroxides

26. 4 Groups Periodic Table Group One Group Two Group 7
Alkali metals
Group Two
Alkaline earth metals
Group 7
Halogens
Group 8 (O) Noble Gases

27. Demonstration of the reaction with water of lithium, sodium
Alkaline Metals
Demonstration of the reaction with water of lithium, sodium
and potassium.

28. Sodium Sodium + Oxygen  Sodium oxide
Sodium + Water  Sodium Hydroxide + Hydrogen gas
Stored in oil to prevent them from reacting with air or water

29. Group 2 Alkaline Earths Group 2 Reactive ions with a +2 Mg +2
Harder than group one
Burn in air to form oxide
React with water to form hydroxides

30. Beryllium

31. Barium

32. calcium

33. Magnesium

34. Strontium

35. Radium

36. Halogens Group 7 Form -1 ions Cl-1 Reactive Coloured
Chlorine, Bromine, Iodine
React with hydrogen to form acids

37. Chlorine Green gas Chlorine + Hydrogen  Hydrogen Chloride gas
Hydrogen chloride gas dissolves in water to form Hydrochloric acid.
Chlorine reacts with sodium to form Sodium Chloride [Table Salt]

38. bromine

39. iodine

40. Group 18: Noble Gases Group VIII (group 0) of the periodic table
Helium and neon
used to make lighted signs, refrigerants, and lasers
Don’t form ions
not reactive - because they have little tendency to gain or lose electrons.