Quantum Theory

the modern atomic model

Bohr Model of the Atom

a quantum model proposed by Niels Bohr in 1913

It helped to explain why the atomic emission spectrum of hydrogen was not continuous.

the neutrons and protons are located in a central region called the nucleus, and the electrons orbit the nucleus much like planets orbiting the Sun.

Bohr Model

The model worked for hydrogen, but did not work for other elements.

It did not explain the chemical behavior of atoms.

Therefore, the model was flawed.

Louis de Broglie

He proposed the idea that electrons have properties of waves (1924).

This was another application of the wave-particle theory of light.

Because electrons are restricted to a certain space, only certain wavelengths (and energies) are possible.

Heisenberg Uncertainty Principle

It is impossible to know both the velocity and position of a particle at the same time.

The principle puts limits on what can be observed.

Erwin Schrödinger

He derived an equation that treated an electron like a wave.

His model worked well for hydrogen and other atoms.

The wave equation predicts a 3-D region around the nucleus (an atomic orbital) where the electron is probably located.

The Quantum Mechanical Model Atomic Orbital (“electron cloud”)

Region in space where there is 90% probability of finding an electron

Orbital

90% probability offinding the electron

Quantum Numbers

Principal Quantum NumberPrincipal Quantum Number ( nn )

Angular Momentum Quantum #Angular Momentum Quantum # ( ll )

Magnetic Quantum NumberMagnetic Quantum Number ( mmll )

Spin Quantum NumberSpin Quantum Number ( ms )

Principal Quantum NumberPrincipal Quantum Number ( nn )

Specifies the principal energy level

Size of the orbital

n2 = # of orbitals in the energy level

1s

2s

3s

Energy sublevels

The other quantum numbers determine shape of the energy sublevel orientation of the orbital the exact orbital an electron is located in the spin of the electron

The energy sublevels are labeled as s, p, d, and f.

Each sublevel can contain a maximum of 2 electrons.

Shapes of s, p, and d-Orbitals

Arrangement of sublevels within the levels Level 1 – s only Level 2 – s and p

Level 3 – s, p and d Level 4 - s, p, d and f