Quantum theory

Electromagnetic waves are emitted by hot objects. For example, as a metal is heated, it first

emits heat (infrared radiation), and then begins to glow different colors, (visible light). As

barium and strontium are heated, a green and red glow appears, (fireworks).

Planck’s Theory

Planck proposed that the amount of energy that an object emits or absorbs is restricted. He

called each piece of energy a quantum.

eg. The energy absorbed or emitted by atoms are quantized; “restricted”

➢ If a car’s fundamental quantum of energy is 10 km/hr, then a car that has 7

quanta will move at a speed of 70 km/hr.

Einstein’s Photoelectic Effect

As light shines on a metal, energy from the light causes electrons from the metal to be

ejected. This is the photoelectric effect. Einstein proposed that light consists of quanta of

energy that behaves like tiny particles of light. He called these particles of light photons.

The amount of quanta that a photon has will determine if an electron is ejected from the

metal.

Bohr’s Model

Bohr proposed that the energy of each electron in an atom

must be quantized.

eg. Electrons are only allowed to spin in certain orbits

depending on the amount of energy it has.

Each energy level (orbital) is given a quantum number, n.

The lowest energy level, (closest to the nucleus) is called

the ground state, n = 1.

• When an electron absorbs energy, it jumps to a

higher energy level called excited state.

• When energy is released or emitted, the electron

falls back to a lower energy level.

Disadvantage: the position of an electron in an orbit cannot be observed or measured.

Electrons are always moving from one level to another.