Na. Mg and Al are the elements having one, two and three valence electrons respectively. Which of these elements has the largest atomic radius? Justify your answer stating reason for each.
Na. Mg and Al are the elements having one, two and three valence electrons respectively. Which of these elements has the largest atomic radius? Justify your answer stating reason for each.
1. Atomic radius
Atomic radius is used to represent the size of an atom. Atoms having a larger size will have a higher radius. An increase in the effective nuclear charge means that the nucleus is pulling the electrons towards it with more force. There are two forces acting in an atom which are the electron-electron repulsion and the electron-nucleus attraction. The repulsive force causes an increase in the atomic radius and the attractive force causes a decrease in atomic radius.
As the effective nuclear charge increases, the nucleus-electron attraction outweighs the electron-electron repulsion and therefore, the size of the atom decreases.
2. Trend in atomic radius
- Since all the electrons are placed in the same shell, the atomic radius of atoms decreases from left to right across a period.
- In a periodic table, the atomic radius of atoms increases from top to bottom within a group.
3. Comparing the radius of Sodium, Magnesium, and Aluminium
Sodium , Magnesium and Aluminium belong to the same period which is the third period of the periodic table. Sodium belongs to the 1st group, Magnesium belongs to the second group and Aluminium belong to the 13th group.
For the elements in the same period, the electrons are added to the same valence shell. Therefore, the effect of increase in nuclear charge outweighs the effect of increase in number of electrons increasing the effective nuclear charge. Therefore, size of an atom decreases across a period from left to right and the elements in the first group will have the highest radius in the period.
Therefore, among the given elements, Sodium (Na) will have the highest radius as compared to Magnesium and Aluminum.
1. Atomic radius
Atomic radius is used to represent the size of an atom. Atoms having a larger size will have a higher radius. An increase in the effective nuclear charge means that the nucleus is pulling the electrons towards it with more force. There are two forces acting in an atom which are the electron-electron repulsion and the electron-nucleus attraction. The repulsive force causes an increase in the atomic radius and the attractive force causes a decrease in atomic radius.
As the effective nuclear charge increases, the nucleus-electron attraction outweighs the electron-electron repulsion and therefore, the size of the atom decreases.
2. Trend in atomic radius
- Since all the electrons are placed in the same shell, the atomic radius of atoms decreases from left to right across a period.
- In a periodic table, the atomic radius of atoms increases from top to bottom within a group.
3. Comparing the radius of Sodium, Magnesium, and Aluminium
Sodium , Magnesium and Aluminium belong to the same period which is the third period of the periodic table. Sodium belongs to the 1st group, Magnesium belongs to the second group and Aluminium belong to the 13th group.
For the elements in the same period, the electrons are added to the same valence shell. Therefore, the effect of increase in nuclear charge outweighs the effect of increase in number of electrons increasing the effective nuclear charge. Therefore, size of an atom decreases across a period from left to right and the elements in the first group will have the highest radius in the period.
Therefore, among the given elements, Sodium (Na) will have the highest radius as compared to Magnesium and Aluminum.
