Question

Which of the following sequences regarding ionisation potential of coinage metal is correct?
A. $Cu > Ag > Au$
B. $Cu < Ag < Au$
C. $Cu > Ag < Au$
D. $Ag > Cu < Au$

Answer 1

We know the modern periodic table is based on the properties of elements as function of their atomic number. The properties of the elements are in accordance to the electronic configuration of the elements. Periodic properties are the trend in properties across a period from left to right to down the group. Some of the predominant periodic properties are metallic character, non-metallic character, atomic size, electron affinity, ionization potential and electronegativity.

Complete step by step answer:
Ionization energy is the energy that is needed for removing one mole of electrons from one mole of isolated gaseous atom or isolated gaseous ion. The first ionization energy of an atom (or) molecule is the energy that is needed to remove one mole of electrons from one mole of gaseous atoms (or) ions.
In the periodic table, we can observe that elements present on the right side of the periodic table contain higher ionization energy because their outermost shell is completely filled. We can also observe that elements present on the left side of the periodic table would have less ionization energies because they tend to lose more readily and turn to action. Thus, ionization energy increases from left to right in the periodic table.
We have to know that the ionization energy and the atomic size of an atom are inversely proportional which means that smaller the size of the atom higher would be the ionization energy.
${\text{Ionisation energy}} \propto \dfrac{1}{{{\text{Atomic size}}}}$
So, we know that the ionization energy of the elements decreases when we move the group with an increase in the distance between the outermost electron and thus nucleus due to the decrement in the effective nuclear charge. The amount of energy that is needed to ionize electrons would be least for gold because the atomic size would be maximum. So, the order of ionization potential of coinage metal is:
$Cu > Ag > Au$

So, the correct answer is Option A.

Note: We must remember that the ionization energy of alkali metals is very low and hence, they can easily lose their outermost electron, thereby acting as a good reducing agent. We can predict the reactivity of an atom using the ionization energy and it can be experimentally determined. Energy is liberated out, when an electron is added to an atom.