Trends of Periodic Properties in Periodic Table and Reason of Variation

Moseley gave the Modern Periodic law which states that “Physical and chemical properties of the elements are periodic functions of their atomic numbers”. In the modern periodic table elements have been arranged according to their atomic numbers and as stated above atomic numbers are directly related to their physical and chemical properties. That’s why elements show periodicity in their physical and chemical properties in the periodic table. For example, as we move from left to right in a period, atomic size decreases. The following figure shows the variation of periodic properties of elements.

(Image will be Uploaded Soon)

Although we find some exceptions which do not follow these periodic table trends. The recurrence of similar electronic configuration in the periodic table is the cause behind periodicity. Thus, we can say that elements having similar electronic configurations have similar properties. Periodic trends provide chemists with a quick and easy tool to quickly predict the properties of elements. In this article, we will discuss periodic properties and their trends in the periodic table in detail.

Periodic Trends of Properties of Elements In Periodic Table 

Modern periodic law is the base of periodic trends of properties of elements in the modern periodic table. Following properties of elements show a very clear periodic trend in the periodic table –

• Atomic Radius 

• Ionisation energy 

• Electron affinity 

• Electronegativity 

• Valence electrons 

• Valency 

• Metallic character of the elements 

• Non – metallic character of the elements 

• Reactivity of elements 

• Melting and boiling points of elements 

Now, understand the trends of properties in detail by knowing the reason for the variation of properties.

• Atomic Radius 

Atomic radius is the distance between the centre of the nucleus of an atom to its outermost shell. 

The periodic trend of atomic radius across a period – As we move from left to right in a period, atomic radius gradually decreases.

Reason – As we move left to right in a period the atomic number of the elements increases so nuclear charge increases while the number of shells in elements remains the same. 

Example – 

Exceptional Behaviour – Noble gases show exceptional behaviour. The atomic radii of inter gases suddenly increase as compared to its predecessor halogen atom. The reason for this type of exceptional behaviour is that atomic radius refers to van der Waals radius in the case of noble gases while in the case of other elements it refers to the covalent radius. 

Across a Group – on moving top to bottom in a group, atomic radii gradually increase as nuclear charge and number of shells also increase. 

• Ionisation Energy 

Ionisation energy is the amount of energy required to remove one electron from an atom. First ionisation energy is the amount of energy required to remove one outermost electron from an atom. 

The periodic trend of ionisation energy across a period – As we move from left to right in a period, ionisation energy gradually increases.

Reason – As we move left to right in a period atomic size or atomic radius decreases while nuclear charge increases. 

Example - 

Exceptional Behaviour – Beryllium possesses more first ionisation energy than Boron. Because beryllium has a half-filled s – orbital and more energy is required to remove an electron from half or completely filled orbitals. That is why noble gases also show exceptionally high ionisation energies. 

Across a Group – on moving top to bottom in a group, ionisation energy gradually decreases as atomic radius increases.

• Electron Affinity 

The amount of energy required to add an electron to an atom is called the electron affinity of that atom. In other words, electron affinity is the change in energy when an electron is added to the atom and a neutral atom changes into a negative ion. 

The periodic trend of electron affinity across a period – As we move from left to right in a period, electron affinity gradually increases.

Reason – As we move left to right in a period atomic size or atomic radius decreases while nuclear charge increases. 

Exceptional Behaviour – Beryllium does not form a stable anion, so it releases less energy than boron by adding an electron. While nitrogen neither releases nor requires a significant amount of energy on adding an electron so it has electron affinity almost equal to zero. 

Across a Group – on moving top to bottom in a group, electron affinity gradually decreases. 

• Electronegativity 

Electronegativity is a measure of the ability of an atom or molecule to attract pairs of electrons in the context of a chemical bond. 

Across A Period – As we move left to right across a period, electronegativity increases in the periodic table. Fluorine is the most electronegative element. 

Reason – As the nuclear charge increases of an atom, its electron loving character also increases. 

Example –

Across A Group – As we move top to bottom in a group, electronegativity decreases. 

• Valence Electrons 

Electrons present in the outermost shell of an atom are called valence electrons of that atom. 

Across A Period – As we move left to right across a period in the periodic table, the number of valence electrons increases.

Example –

Across A Group – Across a group, valence electrons remain constant. It means elements present in the same group have the same number of valence electrons. For example, hydrogen, lithium, and sodium elements are present in the 1st group and have the same number of valence electrons which is one. 

• Valency 

Valency is the combining capacity of an atom.

Across a Period – on moving left to right across a period in the periodic table, first valency increases then decrease. 

Example –

Across A Group – There is no change in valency across a group. Elements of the same groups show the same valency.

• Metallic Character of The Elements 

Across a Period – As we move left to right across a period in the periodic table, the metallic character of elements decreases. 

Example –

Across a Group – As we move top to bottom in a group of the periodic table, the metallic character of elements increases. 

• Non-Metallic Character of The Elements 

Across a Period – As we move left to right across a period in the periodic table, the non-metallic character of elements increases. 

Example –

Across a Group – As we move top to bottom in a group of periodic tables, non-metallic character decreases.

Example -

• Reactivity of Elements 

The reactivity of metals depends on their electropositive character. So, more is the metallic character, more is the electropositive nature of the element and more is its reactivity. As metallic character decreases across a period left to right, reactivity also decreases. Although reactivity of nonmetals increases on moving left to right across a period. Thus, we can conclude, as we move left to right in a period, the reactivity of elements gradually decreases up to group thirteen and then starts increasing. 

• Melting And Boiling Points of Elements 

Melting and boiling points of metals decrease gradually from top to bottom in a group. While melting and boiling points of nonmetals increase on moving from top to bottom in a group of the periodic table.  

Conclusion

The periodic properties in the periodic table develop a base in order to understand the nature of elements in an efficient way. The above article covers all the important trends of properties in the periodic table. These are the basic concepts of chemistry that are helpful in grasping the different concepts of organic chemistry.