Periodic Trends

Definition: Periodic Table is a table of elements arranged in order of increasing proton number to show the similarities of chemical elements with related electronic configurations.

-The elements are arranged in increasing order of their proton(atomic) number in seven horizontal rows called 'periods'.

-Chemically similar elements are arranged in eighteen vertical columns called 'groups'.

-Group number indicates the number of electrons in the outermost principal quantam shell of an atom.

-Period number indicates the number of electron shells in an atom.

-A dividing(staircase-shaped) line seperates the metals and non-metals(metals lie to the left of the line and non-metals to the right)

-Hydrogen(H) is an exception as it is a non-metal and is placed in the top left-hand corner of the table.

-Semi-metals or metalloids are elements with both metallic and non-metallic characteristics and therefore fall along the staircase line.

Postition of an element in periodic table

-The position of an element depends on its proton(atomic) number and hence on its electronic configuration.

-The number of outermost orbital(n) of an atom indicates the period number.

-The total number of electrons in that outermost orbital indicates the group number of an element.

(Going downward from left to right,each new period means addition to another electron shell)
(From one group to another from top down,electrons are added in the same shell gradually filling up the shell.)

-For a given proton number which is equal to the number of electrons,the arrangement of electrons can be derived(using 2n^2).

(The number of shells will determine the element's period number.)
(And the number of electrons in the outermost shell will determine the group number.)

-Thus,position of an element can be derived from the proton number or electronic arrangement.

Relationship between group number and ionic charge

-The group number of an element depends on the total number of electrons present in the outermost shell or valence shell.

-Ionic charge of an element depends on the total number of electrons in that shell.

-If number of electrons in the valence shell is less than 5,then the ionic charge or valence will be same as the number of electrons in that shell.

-If it is equal to or greater than 5,then ionic charges will be 8 minus the number of electrons.

Similarities between elements in the same group

-The elements in the same group have same number of valence electrons.

-Due to the similarity in the number of valence electrons,elements in the same group have similar chemical properties.

-Each element has 2 electrons in the outermost shell which they tend to lose to attain a stable,noble gas configuration.

-Hence,they are very reactive and are not found free in nature.

-Because they tend to lose 2 electrons,they all form ions with a +2 charge i.e become bivalent and hence undergo similar chemical reactions.

-Thus, the similarity in their electron configurations causes them to share the same properties.

Metallic and non-metallic character of elements

-An element's position in the periodic table indicates how metallic or non-metallic,an element is relative to other elements.

-The general trend in metallic/non-metallic properties in the periodic table is as follows:
(Metallic character increases from top to bottom within a group.)
(Metallic character decreases from left to right across a period.)

-For example,Caesium(Cs) is one of the most metallic elements. If we exclude noble gas, Fluorine is the most non-metallic element.

Relationship between group number,number of valence electrons and metallic/non-metallic character

-An atom is said to be metal if it loses one or more electrons when supplied with energy.

-Similarly, an atom is said to be non-metal if it gains one or more electrons supplied with energy.

-Number of valence electrons in outer shell increases progressively by one per group across a period with increasing non-metallic character.

-Valence of an element(increases from c1 to 4, from group to V and then)(decreases from group V to V down to zero for noble gases)

-Elements of group ,, are metallic, while groups V,V,V,V are non-metallic.