Q14.46 P - Chemistry: Molecular Nature Of Matter And Change

Question

Fluorine lies between oxygen and neon in Period 2. Whereas atomic sizes and ionization energies of these three elements change smoothly, their electronegativities display a dramatic change. What is this change, and how do their electron configurations explain it?

Step-by-Step Solution

Answer

Fluorine has a smaller size than oxygen and neon, and the ionization energy of oxygen is less than fluorine. Neon has maximum ionization energy, and its electronic configuration shows how many electrons are gained or lost to complete the octet.

Step 1: Atomic size

It is defined as the size of an atom that decreases across a period from left to right, because the valence shell increases and the effective nuclear charge increases.

Step 2: Atomic size of oxygen, fluorine, and neon

In this period, the atomic side decreases. Fluorine is smaller than oxygen, because it is present after oxygen and has a more effective nuclear charge than oxygen.

But fluorine has a smaller size than neon even if fluorine is present before neon, because it alone has a filled octet in its outermost shell and is stable, and does not gain and lose electrons, so that its effective nuclear charge decreases.

Step 3: Ionization energy

It is defined as the energy required to remove the electrons from the molecule. The ionization energy increases from left to right in a period because of an increase in a nuclear charge that requires more energy to remove electrons.

Step 4: Ionization energy of fluorine, oxygen, and neon

Fluorine has more ionization energy than oxygen because of a more effective nuclear charge, and the ionization energy increases across a period. Neon has very high ionization energy as the octet is complete; it is very stable and a noble gas.

Step 5: Electronic configuration

It is the arrangement of electrons around an atom’s atomic nucleus in specific orbits.

Electronic configuration of oxygen: $1s^{2}2s^{2}2p^4$ 

so, as per electronic configuration, oxygen has six valence electrons and gains two electrons to complete an octet.

Electronic configuration of fluorine:  $1s^{2}2s^{2}2p^5$

So, as per electronic configuration, fluorine has seven valence electrons and so it needs only one electron to become stable.

Electronic configuration of neon: $1s^{2}2s^{2}2p^6$

So, it is clear from the electronic configuration that neon has a complete octet in the outermost shell, and so is a stable gas.