Question

Among Na$^{+}$, Na, Mg and Mg$^{2+}$, the largest particle is:
a.) Mg$^{2+}$
b.) Mg
c.) Na
d.) Na$^{+}$

Answer 1

Hint: To know the largest particle, there are several factors to be considered i.e. effective nuclear charge along the period, and the atomic size of element. The atomic size of Na is 154 pm and for magnesium, it is 130 pm.
Complete step by step solution:
Now, if we see the position of Na and Mg in the periodic table, Both the elements belong to the period 3, but Na belongs to the group 1 and Mg to the group 2.

Now, if we move from left to right along a period in the periodic table, the size of element decreases, whereas the effective nuclear charge increases.
From this point it is clear that the size of Na is larger than Mg.
Talking about the ions of both the elements i.e. Na$^{+}$ and Mg$^{2+}$, as we know the size of any ion is smaller than its parent element. So, the size of Na$^{+}$ and Mg$^{2+}$ is smaller than Na and Mg respectively.

Thus, the decreasing order of size is written as: Na>Mg> Na$^{+}$>Mg$^{2+}$.
Therefore, the largest particle is Na. The correct option is C.

Note: Don’t get confused between the atomic size and atomic number. Atomic number of sodium is 11, and for magnesium it is 12, whereas atomic size is the distance between the centre of nucleus of an atom and the outermost shell of the atom, and atomic size is written in Pico meters (pm).