Nota Terkini

Wednesday, May 06, 2009

[Chemistry Form 4] Periodic Table Of Elements

The periodic table of elements presents an organised display of all known elements. It has horizontal rows, called periods, and vertical columns, called groups, which arrange the elements in such a way that those with similar properties fall under the same group.

Element in the same group have the same number of valence electrons.
Eg: Elements in the first group have one valence electron while those in the second group have two valence electrons.

In addition, elements arranged along the same period share a common feature, i.e. the same number of electron shells.
Eg: Elements in the first period have one shell to contain their electrons while those in the second period have two shells to contain theirs.

Another arrangement evident in the periodic table is that metals are on the left and non-metals are on the right.

The need to organise elements into groups based on their properties arose when more and more elements were made known. Thus, scientists began to develop the periodic table of elements.

Below are scientists with their respective contribution to the development of the periodic table;

1. Lothar Meyer (1830-1895)
This German chemist recognised periodic behaviour based on his graphs of the atomic volume of elements against their atomic weight.

2. Dmitri Mendelev (1834-1907)
This Russian chemist made a table of elements and left a gap for elements that had not yet been discovered.

3. Antoine Lavoisier (1743-1794)
This French chemist classified elements into four groups - gases, non-metals, metals and earths.

4. John Newlands (1837-1898)
This English chemist's law of octaves stated that when elements were placed in the increasing order of atomic weight, the properties of elements fell into a pattern at regular intervals.

5. Henry J. G. Moseley (1887-1915)
This British chemist rearranged the elements in order of increasing atomic number.

6. Johann Dobereiner (1780-1849)
This German chemist proposed the law of triads, which stated that elements came in groups of three.

3 comments:

  1. What about listing the scientists in chronological order so that the development of Periodic Table is clearer?

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  2. help me!!! i still d0nt understand..:-(..

    ReplyDelete
  3. ya me also still dont understand

    ReplyDelete