The potential energy curve for the H₂ molecule as a function of internuclear distance is :

Solution

Chemistry ma’am · 5 steps

Two H atoms attract, then repel, so energy dips to a minimum at the bond length. Look for the valley.

1. Far apart. When the two H atoms are very far apart, they do not interact. The energy is flat at its starting value, usually taken as zero.
2. Coming closer. As they approach, each nucleus attracts the other atom's electron. This attraction is stronger than the repulsions, so the energy falls.
3. The minimum. At 74 pm attraction and repulsion balance, and the energy is lowest. This distance is the bond length, and the depth of the dip is the bond energy, 435.8 kJ mol⁻¹.
4. Too close. Push them closer still and the nucleus–nucleus and electron–electron repulsions take over. The energy rises steeply, so the curve goes up on the left side.

   Option	Shape of the curve	Matches H₂?
   (a)	Falls all the way, no minimum	No, only repulsion
   (b)	Rises all the way, no minimum	No, energy should go up at short distance
   (c)	High at short distance, dips to a minimum, levels off at large distance	Yes
   (d)	Rises to a maximum, then falls	No, upside down

5. So. Only (c) shows a high-energy wall at short distance, a well at the bond length, and a plateau at large distance. That is the curve for H₂.

The idea to keep. A bond forms only where energy is lowest. Any stable molecule's energy–distance curve has a well: its position is the bond length and its depth is the bond energy.

Answer from the NTA final answer key. Solution by PrepWiser.