In modern periodic table; arrange the third row elements Na, Mg, Al and Si in the increasing order of their atomic size:
Na > Mg > Al > Si
Al > Si > Na > Mg
Si > Al > Mg > Na
Na > Al > Si > Mg
In modern periodic table; arrange the third row elements Na, Mg, Al and Si in the increasing order of their atomic size:
Na > Mg > Al > Si
Al > Si > Na > Mg
Si > Al > Mg > Na
Na > Al > Si > Mg
The correct option is A Na > Mg > Al > Si
Atomic size
Atomic radius is used to express the size of an atom. The shortest distance between the center of the nucleus of an atom to the outermost electron is calculated as the atomic radius. It cannot be determined exactly due to uncertainty in position of an electron. It is calculated as covalent radius, metallic radius or van Der Waals radius.
The atomic size of an element decreases across a period. This is because the electron is being added to the same electronic shell. The increase in number of protons in nucleus causes an increase in nuclear charge. The effect of increase in nuclear charge is greater than addition of electron. Therefore, the effective nuclear charge on the valence electron increase and the nucleus pulls the electron with more strength. Therefore, size of the atom decreases.
Down a group, the new shells are added in successive periods. Therefore, the effect of increase in number of shells outweighs the effect of increase in nuclear charge. Therefore, size of the atom increases.
The given elements belong to the third group in modern periodic table.
Explanations for wrong answers
(B) Aluminium (Al) and Silicon (Si) belong to 13th and 14th group respectively. Sodium (Na) and Magnesium (Mg) belong to the 1st and 2nd group. Since atomic size decreases across a period, the size of Aluminium and Silicon will be less than that of Sodium and Magnesium. Therefore, option (B) is incorrect.
(C) Sodium belongs to the first group. Therefore, it will be largest atom in the period. Therefore, option (C) is wrong.
(D) Magnesium belongs to the 2nd group. Aluminium (Al) and Silicon (Si) belong to 13th and 14th group respectively. Therefore, size of Magnesium will be larger than the size of Aluminium and Silicon. Therefore, option (D) is incorrect.
Explanation for the correct answer
(A) The atomic size decreases across a period. Therefore, for the elements of a particular period, the atomic size is inversely proportional to their atomic number. The decreasing order of atomic number of the given third row elements is Si > Al > Mg > Na.
Therefore, the order of their atomic size is Na > Mg > Al > Si
The correct option is (A) Na > Mg > Al > Si.
Na > Mg > Al > Si
Atomic size
Atomic radius is used to express the size of an atom. The shortest distance between the center of the nucleus of an atom to the outermost electron is calculated as the atomic radius. It cannot be determined exactly due to uncertainty in position of an electron. It is calculated as covalent radius, metallic radius or van Der Waals radius.
The atomic size of an element decreases across a period. This is because the electron is being added to the same electronic shell. The increase in number of protons in nucleus causes an increase in nuclear charge. The effect of increase in nuclear charge is greater than addition of electron. Therefore, the effective nuclear charge on the valence electron increase and the nucleus pulls the electron with more strength. Therefore, size of the atom decreases.
Down a group, the new shells are added in successive periods. Therefore, the effect of increase in number of shells outweighs the effect of increase in nuclear charge. Therefore, size of the atom increases.
The given elements belong to the third group in modern periodic table.
Explanations for wrong answers
(B) Aluminium (Al) and Silicon (Si) belong to 13th and 14th group respectively. Sodium (Na) and Magnesium (Mg) belong to the 1st and 2nd group. Since atomic size decreases across a period, the size of Aluminium and Silicon will be less than that of Sodium and Magnesium. Therefore, option (B) is incorrect.
(C) Sodium belongs to the first group. Therefore, it will be largest atom in the period. Therefore, option (C) is wrong.
(D) Magnesium belongs to the 2nd group. Aluminium (Al) and Silicon (Si) belong to 13th and 14th group respectively. Therefore, size of Magnesium will be larger than the size of Aluminium and Silicon. Therefore, option (D) is incorrect.
Explanation for the correct answer
(A) The atomic size decreases across a period. Therefore, for the elements of a particular period, the atomic size is inversely proportional to their atomic number. The decreasing order of atomic number of the given third row elements is Si > Al > Mg > Na.
Therefore, the order of their atomic size is Na > Mg > Al > Si
The correct option is (A) Na > Mg > Al > Si.
