Subject: Chemistry Chapter: Periodic classification of elements
Topic: Trends in the modern periodic table
By now you know all about the periodic table. But did you know the periodic table has some patterns and trends? Learning about these patterns will make your reading of the periodic table much easier. So let us learn more about the modern periodic table trends.There are specific patterns present in the arrangement of elements in the periodic table. These periodic table trends arise out of the specific arrangement of elements due to the Periodic Law. Studying these trends, allows chemists, scientists and even us to quickly identify certain properties of an element. They exist because our periodic table places elements that have similar characteristics together. There are certain exceptions to the trend also. Let us look at a few of these trends that we find in our periodic table.Valency
One of the trends in the modern periodic table is that of the valency of an atom. As you already know, the valency of an atom is the number of electrons it has in its outermost shell or the number of atoms in requires to complete its outermost shell. However one can determine the valency of an element simply from its position in the periodic table. The group that the element is placed in usually indicates its valency. Let us look at a few examples to understand this trend.
All alkali metals in group one, have the valency one and form monovalent bonds
The alkali earth metals making up group two, have two electrons in the last orbit and are bivalent
Similarly, all Halogens in group 17, have the valency of one (8-7) and are monovalent
Atomic Size
Atomic size is the distance between the centre of the nuclei and its outermost orbit. In simple terms, it is the radius of an atom. It is noticed that the atomic size of elements decrease as we move from left to right in a period. This is because the electrons increase hence increasing the nuclear charge.
When the nuclear charge is stronger, the nucleus pulls the electrons closer to itself so reducing the atomic radii. As opposed to this when one moves from the top to bottom of a group, the atomic size of elements increases. This is because the number of shells of the atom increase, increasing their radii.Electronegativity
Electronegativity is the ability of an atom of any element to attract a shared pair of electrons in a chemical bond, towards itself. It is a measure of atom’s tendency to form a molecule by attracting electrons to itself. The most electronegative element is Florine and the least is Caesium.
So by this, you can probably deduce that as you move in a row (period) from left to right the electronegativity increases. And from top to bottom in a column (group) it will decrease. This is because when the number of shells increases as we go down a group, so the pull of the nucleus to attract electrons decreases.
Metallic and Non-metallic Properties
In the periodic table a zigzag line, across the table, separates the metals from the non-metals. As you will be able to notice on the periodic table, the metals such as Magnesium, Aluminium, Iron etc are clustered towards the left side of the table. And the non-metals such as Florine and Sulphur are found on the right.
Then there are the metalloids also known as the semi-conductors. These borders the zigzag line on the periodic table. These have some properties of metals and some of the non-metals. Some examples are Boron, Arsenic, Tellurium etc.
Let us learn more about them in this video.
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