ATOMIC THEORY PART 2 (SEC. 1.2 SECOND HALF)

The first spectroscopy

• Robert Bunsen and Gustav Kirchhoff

• Revealed that each element has its own unique line spectrum

The unique line spectrums of elements are significant because

they indicate that the electrons can only exist at discrete energy levels

Rutherford model was based on classical physics…

• in this model the electron could emit or absorb any quantity of energy

• If this were true the emission spectrum of every element would be a continuous spectrum

Niels Bohr modified___model based on his work with___

Rutherford,hydrogen

Bohr’s model of the atom

• electrons are found in fixed energy levels around the nucleus

• Electrons tend to stay in lower energy levels (ground state, most stable) but can move to higher levels when they can energy (excited state)

• Almost immediately after electrons enter the excited state they return to ground

• In this process, they emit energy through light

Visible spectrum colour energies

• violet is the highest energy light and red is the lowest

• (Shorter wave length = higher energy)

James Chadwick’s discovery

• from the time of Rutherford, it was known that the mass of the atom was a bit more than double the mass of the protons

• Since almost the entire mass was concentrated in the nucleus, there must be another particle in the nucleus with a mass similar to the proton

• He discovered the neutron. It has almost the same mass as a proton but no charge

Summary of the Bohr-Rutherford model

• Small, dense, heavy nucleus containing protons and neutrons (the nucleus is positively charged).

• Electrons orbit the nucleus in fixed energy levels (like planets orbiting the sun); the higher the energy level, the more energy an electron has

Atomic number (z)

• the number of protons in an atoms nucleus

• For a neutral atom # of electrons = # of protons

Mass number (A)

• total # of protons & neutrons in the nucleus of an atom

• number of neutrons = A - Z

Atomic number and mass calculations examples