The Tale of Two Atoms

What happens when two atoms interact?

1. What is an atom?

The simple view. Based on the Bohr model of the atom.

2. Electrostatic interactions

Opposite charges attract Like charges repel

3. The sum of the net repulsion and attractions can be graphed.

Potential-well diagram

4. The two atoms form a bond where the attraction is maximized.

5. There are different types of kinetic ienergy on a microscopic level.

KE tot = E trans + E vib + E rot + E elec

6. According to Boltzmann distribution curve, the kinetic energy of a system is distributed among the particles. The average KE of the particles is defined as the temperature of the system.

Boltzmann Distribution

7. At temperatures above absolute zero molecules will begin to populate vibrational states.

8. The bottom line is that at elevated temperatures the bonds are more likely to break.

After they are broken they are free to form new bonds with other atoms.

That is a

chemical reaction

.

Bond breaking is an

endothermic

process.

You must put energy into the molecule to cause vibrations large enough to break the bond, i.e. the atoms reach infinite bond distance.

Bond forming is

exothermic

process.

When two atom fall into the potential well, they go to a lower energy state and the energy is lost to the surroundings.

Observe the following reactions.

Li + H20

Sucrose + Sulfuric Acid

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