BOHR MODEL OF THE ATOM

ATOMIC SPECTRA• Ground state: the lowest energy

state of an atom• Excited state: state in which an

atom has a higher potential energy than it has in its ground state

• When an excited atom returns to its ground state, it gives off the energy it gained in the form of EM radiation (light)• Ex: neon signs

• Light is given off in very definite wavelengths• Line-emission spectrum: series of

specific wavelengths of emitted light created when the visible portion of light from excited atoms is shined through a prism

BOHR MODEL

Niels Bohr (1913)• Danish physicist • Proposed a model of the hydrogen atom that

linked the atom’s electron with photon emission• Electrons exist only in orbits with definite,

fixed amounts of energy called energy levels

Recall:What is a photon?

• While in orbit, electrons can neither gain nor lose energy• Electrons can jump from energy level to

energy level• Electrons can only gain or lose certain

amounts of energy

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6

• Energy of photon depends on the difference in energy levels• Energy is greater when it is

farther from the nucleus• Energies of atoms are fixed &

definite quantities

• The emission spectrum of each element is unique• Can be used to identify unknown samples• “Atomic Fingerprint”

Bohr’s calculations only worked for hydrogen L

THE QUANTUM MODEL OF THE ATOM

ELECTRONS AS WAVES

• Louis de Broglie• 1924 • Applied wave-particle theory to electrons• Suggested that electrons be considered waves confined to the

space around an atomic nucleus

THE HEISENBERG UNCERTAINTY PRINCIPLE

Werner Heisenberg• 1927 – German theoretical physicist• Studied finding electrons by their

interactions with photons• Result: uncertainty in trying to locate

an electron or any other particle• Heisenberg uncertainty principle:

states that it is impossible to know both the position and velocity of an electron or any other particle at a given time

THE SCHRODINGER WAVE EQUATION

• Erwin Schrodinger• 1926 – Austrian physicist• Developed an equation that

treated electron in atoms as waves

( ) σ3/2 Zπ

11s 0

-= eΨ a

• Solution to Schrodinger equation is known as a wave function• Gives the probability of finding

an electron at a given place around the nucleus

• Electrons do not travel in neat orbits• Orbital: 3-dimensional region

around the nucleus that indicated the probable location of an electron

• Quantum theory: describes mathematically the wave properties of electrons and other small particles

THINK-PAIR-SHARE

Bohr vs. Quantum?Compare & contrast the Bohr and

Quantum Model of the atom