Monday, 5 January 2015

4.1 The Periodic Table of Elements

Periodic Table of elements
■ A form of classifying elements systematically by placing elements with similar features in the same group.
■ In Periodic Table

The elements are arranged in order of increasing proton number.

Element with same chemical properties are placed in the same group.

The characteristic of the element and its compounds can be predicted, thus making the study of chemistry easier and more systematic.
■ Historical development of the Periodic Table

Several scientists have contributed greatly to the development of the Periodic Table in the eighteenth and nineteenth centuries.

The following table shows the contribution of scientists in the development of the Periodic Table.
Antoine Lavoisier
(1743 – 1794)
He wrote the first extensive list of elements containing 33 elements.
He distinguished between metals and non-metals.
His classification was unsuccessful because light, heat and a few other compounds were also considered as elements.
Johann W.Dobereiner
(1780 - 1849)
He proposed the Triad Law, whereby he classified element with similar properties in the same group.
Lithium, sodium and potassium formed a triad.
Calcium, strontium and barium formed a triad.
Chlorine, bromine and iodine formed a triad.
John Newlands
(1837 - 1898)
He proposed the Octave Law, which classified element according to increasing relative atomic mass.
Lothar Meyer
(1830 - 1895)
He successfully compiled a Periodic Table of 56 elements based on the periodicity of properties such as molar volume when arranged in order of atomic weight.
He plotted the graph of atomic volume against the atomic mass of each element and suggested that elements occupying corresponding positions on the graph showed similar chemical properties.
Dimitri Mendeleev
(1834 – 1907)
He arranged elements according to increasing atomic numbers in horizontal groups, called periods.
He suggested that the properties of elements varied periodically. Element with similar chemical properties were placed in vertical rows called groups.
He left empty space for undiscovered element at that time.
He was able to predict the properties of the undiscovered elements.
Henry Moseley
(1887 - 1915)
He arranged the elements according to the ascending proton numbers.
■ This video contains information about the development of the Periodic table that we have today.

Modern Periodic Table
■ Periodic Table

Arranged according to ascending proton numbers of the elements.

Elements with the same chemical properties are placed in the same group.

The animation below shows the Modern Periodic Table.

The animation below shows the summary of information which can be obtained from the Periodic Table.
■ Group

Vertical columns of the Periodic Table.

Each member of a group shows similar chemical properties.

Physical properties show a gradual change when descending the group.

Some of the groups have special names.
Group Special name
Group 1 Alkali
Group 2 Alkali earth metals
Group 17 Halogens
Group 18 Noble gases
Group 3 to 12 Transition elements
■ Periodic

Horizontal rows of the Periodic Table.

The proton number increase by one across the period from left to right.

Contain elements with chemical and physical characteristics which change progressively from metal to non-metal.

Example of elements in period 3:
■ This video contains information about group and period in the periodic table.

The electron arrangement of elements in the Periodic Table
■ Arrangement of elements in the Periodic Table (first 20 elements)

From the table, the elements in a group
○ have the same valence electrons
○ have the same chemical properties
○ exhibit physical properties which change gradually down the group 

From the table, the elements in the same period have the same number of filled electron shells.
■ Relationship between the arrangement of electrons in the atom of each element to its group and period.

By knowing the proton number of an element, we can write the electron arrangement of the element.

Thus, the Group and Period it is placed in the Periodic Table can be determined.
■ This video describes the relationship between the electrons arrangement to its group and period.

✍ Worked-example 4.1(a)

An element T has a proton number of 12 and nucleon number of 24. What Group and Period does it occupy in the Periodic Table of Elements?
The number of electron = proton number = 12
Electron arrangement: 2.8.2
Element T has 2 valence electron. Hence element T is in Group 2 of the Periodic Table.
Element T has 3 filled electron shells. Hence element T is in Period 3 of Periodic Table.

⇲ For exercise(objective and subjective), download for free on Android OS.

No comments:

Post a Comment