Electrons in AtomsDevelopment of Atomic Models

Things Rutherford’s Atomic Model Could Explain

Protons and Neutrons composed the atomic nucleus

Electrons move around the nucleus in the same way that planets revolve around the sun

And Things it Couldn’tThe chemical properties of elements:

Why do metals give off specific colors when heated?

He needed to better describe the behavior of electrons!

Rutherford’s Model Changed!1913 – The Bohr Model

Energy of an atom changes when it absorbs or emits light

Electrons are only found in specific circular paths, or orbits around the nucleus Each possible orbit have fixed energy levels

Can an electron move into different energy levels?

To move from one energy level to another, they need to gain or lose the right amount of energy

A quantum of energy is the amount of energy required to move an electron from on energy level to another

Another Atomic Model is Developed

1926Schrodinger (Used Mathematical Solutions)Quantum Mechanical Model – determines

the allowed energies an electron can have and how likely it is to find the electron in various locations around the nucleus

Where can you find electrons?Atomic Orbitals – region in space in which

there is a high probability of finding an electronPrinciple energy levels (n = 1)Energy sublevels (1)

Maximum numbers of electronsEnergy level n # of electrons

1 2

2 8

3 18

4 32

SublevelsSublevel corresponds to a different shaped

orbital

Change Proceeds to Lowest EnergyIn an atom, electrons make the most stable

arrangementElectron Configuration- the ways in which

electrons are arranged in various orbitals around the nucleus of an atom

Aufbau PrincipleElectrons occupy the lowest energy orbital

first

Pauli Exclusion PrincipleAn atomic orbital may describe at most 2

electrons

Hund’s RuleElectrons occupy orbitals of the same energy

in a way that makes the number of electrons with the same spin direction as large as possible

Energy Levels, Sublevels and OrbitalsA sublevel is a region IN the energy level4 possible sublevelsOrbital is a region in the sublevel. Each

orbital can hold only 2 electrons

S 1 orbital 2 electrons

p 3 orbitals 6 electrons

d 5 orbitals 10 electrons

f 7 orbitals 14 electrons

What is light?Newton believed it was made up of particles

BUT it was proven to consist of waves.Wave cycles start at zero, increase to the

highest value, passes through zero to reach its lowest value, and returns to zero again.

3 Properties of WavesAmplitude – the wave’s height from zero to

the crest (highest point of the wave)

Wavelength – distance between the crests

Frequency – the number of wave cycles to pass a given point per unit of time

Calculate Wavelengthλ= c/ν

λ= Wavelength (m)C= Speed of Light (2.998 x108 m/s)

ν= Frequency (/s)

Electromagnetic Spectrum

Practice!Calculate the wavelength of the yellow light

emitted by a sodium lamp. The frequency of the radiation is 5.10x1014 /s.

What is the frequency of radiation with a wavelength of 5.00x10-8m?

Atomic SpectraWhen atoms absorb energy, electrons move

into higher energy levels. These electrons move into higher energy levels

and lose energy by emitting light and returning to the lower energy levels.

Electron EnergyGround State – Lowest possible energy of an

electronn= 1

When an electron absorbs energy it enters an excited stateN= 2,3,4,5,6 etc.

A quantum of energy in the form of light is emitted when an electron drops to a lower energy levelElectronic Transition

Quantum MechanicsEinstein proposed that light could be

described as quanta of energyLight quanta are known as particles

Classical vs. QuantumClassical Mechanics

Describes the motions of bodies much larger than atoms

Quantum MechanicsDescribes the motions of subatomic particles

and atoms as waves

Heisenberg Uncertainty PrincipleIt is impossible to know exactly both the

velocity and position of a particle at the same time