Periodic Trends in Properties of Elements- Atomic Radii, Ionic Radii, Ionization Enthalpy

The rate at which a chemical substance or an element undergoes a chemical reaction is known as reactivity. The electrons between the elements are shared, or the elements lose or gain the electrons. The higher the reactivity of the element, the easier it is to combine. Hence the electronegativity and the ionisation energy determine a chemical reaction. In a period, the chemical reactivity decreases on moving towards the right, whereas in a group, chemical reactivity increases on moving downwards. Hence the elements on the left side in the downwards direction are the highly reactive elements. The elements have hydroxides which are basic in nature. The gas elements do not gain or lose their electrons because the electronic configuration is filled. The periodic trends and chemical reactivities of elements are shared below.

Periodic trends and chemical reactivity

Periodic trends refer to the patterns of the properties of the chemical elements. The trends of the elements in a periodic table depend on various factors like electronegativity, ionisation energy, electron affinity, atomic radii, metallic character and chemical reactivity. Some periodic trends and chemical reactivity in the periodic table are as follows – 

• Electronegativity 

It measures the ability of a molecule to gain electrons within a chemical bond. The Pauling scale is used to measure electronegativity. On moving from left to right horizontally in a periodic table, there is an increase in electronegativity. On moving in the downward direction, the electronegativity decreases. An exception in group 3 elements is present where electronegativity increases towards thallium. 

• Ionisation energy 

This energy helps the atoms to remove the electrons. Ionisation energy increases on moving horizontally across a period, whereas on moving in the downward direction, the ionisation energy decreases. 

• Atomic radii 

The distance between the outermost electron and the nucleus is known as the atomic radius. On moving from left to right, it increases, and on moving from top to bottom, it increases. On moving in a diagonal direction,  atomic radius tends to increase. 

• The affinity of electrons 

It refers to the energy that is released when an electron is gained by an atom. It increases on moving from left to right as more energy is released.

• Metallic character

The metallic character of elements in a periodic table tends to increase on moving from top to bottom, and it tends to decrease on moving from the left towards the right. Hence their ability to conduct electricity is determined. 

• Chemical Reactivity

It refers to the energy or the force of a chemical substance to undergo a reaction. The substance can react with itself or with some other substance and release energy. The chemical reactivity on moving from top to bottom increases, and it decreases on moving across. 

The oxidation state of elements in the periodic table 

The state of oxidation of a specific element refers to the degree to which an atom can lose or gain its electrons. The state can either be positive, zero or negative. The term was developed by Antoine Lavoisier. Oxidation and reduction are the two reactions that help in, formally transferring electrons. Reduction refers to a reaction where oxidation decreases. The oxidation state is as high as +8 in certain elements, while it is as low as -4. A pure element will always have an oxidation state of zero. It is also very important to obtain a result of zero upon adding the oxidation states of all atoms of a neutral molecule. The pure non-ionized elements in all their phases exist in zero. In order to determine the oxidation state of elements, the group numbers can be used on the periodic table. The most common oxidation states of elements can be -3, +3 or +5. In order to calculate the oxidation state of certain elements, the formula to be used is ‘charge of ions is equal to the overall oxidation state’.

Trends in chemical reactivity of group 15 elements 

Group 15 of the periodic table consists of elements like nitrogen, phosphorus, arsenic, antimony, bismuth, and moscovium. The family of these elements is known as the nitrogen family. The lighter elements are placed on the top while the heavier ones are present at the bottom. The electronic configuration is ns2np3.  Hence the elements of the group can lose five electrons, or they can gain three electrons. These elements are different from one another completely, yet the general chemical behaviour has certain similarities. The trends in chemical reactivity of group 15 elements are as follows – 

• Reaction with HYDROGEN results in the formation of hybrids
• The type of hydride formed is EH3
• Here, E is equal to N, P, As, Sb, Bi
• When moved in the downward direction, there is a decrease in the stability of hydrides

• Reaction with OXYGEN results in the formation of two different types of oxides which are denoted as E2O3 and E2O5
• Here, E is equal to N, P, As, Sb, Bi
• The oxides present in the higher oxidation state have a more acidic nature
• When moved in the downward direction, its acidic nature tends to decrease

• Reaction with Halogens results in the formation of two different series of salts – EX3 and EX5
• Each trihalide, except NX3, is stable in nature

• Reaction with METALS results in the formation of compounds that are binary
• Here, the metals tend to have an oxidation state of -3 

Conclusion

Periodic trends refer to the patterns of the properties of the chemical elements. The trends of the elements in a periodic table depend on various factors. The state of oxidation of a specific element refers to the degree to which an atom can lose or gain its electrons. In a period, the chemical reactivity decreases on moving towards the right, whereas in a group, reactivity increases on moving downwards. Group 15 of the periodic table is the nitrogen family. When moved in the downward direction, there is a decrease in the stability of hydrides. When moved in the downward direction, acidic nature tends to decrease. Reaction with metals results in the formation of compounds that are binary. The periodic trends and chemical reactivity of elements depend on various factors.