Why does the stability of free radicals decrease as we go from left to right across the periodic table?

Answer 1

The central atoms of free radicals become more electronegative as one moves from left to right across the Periodic Table, decreasing their stability.

It is challenging to quantify the energy of a particular free radical; however, trends can be obtained by examining bond dissociation energies (BDEs).

BDE = 435 kJ/mol for H₃C-H, 431 kJ/mol for H₂N-H, 431 kJ/mol for HO-H, 498 kJ/mol for HO· + ·H, and 565 kJ/mol for F-H, F· + ·H.

A higher BDE indicates a less stable free radical, whereas a lower BDE indicates a more stable free radical.

Consequently, the stability order is

H₃C· > HO· > F· ≈ H₂N·

A free radical's core atom contains just seven valence electrons.

Therefore, both carbocations and free radicals are electron-deficient species.

Free radicals are stabilized by the same mechanisms that stabilize carbocations.

Cation stability declines in the order

HO⁺ > F⁺ > H₃C⁺ > H₂N⁺

Because the F atom is strongly electronegative—that is, it is difficult to remove an electron from an F atom—the F⁺ ion has the highest energy and is the least stable.

Free radicals follow the same pattern: the least stable free radical belongs to the most electronegative element.

Sign up to view the whole answer

By signing up, you agree to our Terms of Service and Privacy Policy

Sign up with email
Answer 2

The stability of free radicals decreases as we go from left to right across the periodic table due to the increasing electronegativity of elements. This leads to a greater attraction for electrons, making it harder for free radicals to exist.

Sign up to view the whole answer

By signing up, you agree to our Terms of Service and Privacy Policy

Sign up with email
Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

Not the question you need?

Drag image here or click to upload

Or press Ctrl + V to paste
Answer Background
HIX Tutor
Solve ANY homework problem with a smart AI
  • 98% accuracy study help
  • Covers math, physics, chemistry, biology, and more
  • Step-by-step, in-depth guides
  • Readily available 24/7