CHAPTER 5ARRANGEMENT OF ELECTRONS IN ATOMS

*Rutherford's model of the atom does not explain how the electrons fill the space

**See Gold Foil experiment pg. 108

Evidence about the configuration of electrons in the orbitals (electron cloud) came from studying light:

Light (electromagnetic radiation) has a dual nature, meaning it behaves like a wave and a particle.

WAVE DESCRIPTION OF LIGHT –

o 1800's scientists believed that light was a beam of energy moving through space in the form of waves

(like waves on a lake when a pebble is thrown in)

*ALL WAVES HAVE 4 CHARACTERISTICS: SEE PAGE

amplitude - height of wave origin to crest

wavelength (λ)- distance between crestsLight is measured in nanometers (nm)

frequency (v) how fast up and down (oscillations)

units: waves/sec, Hertz (Hz), s-1

speed (c) - constant 2.998 x 108 m/s

C = SPEED OF LIGHT (LATIN CELERATA)

Formula: c = λv*

*wavelength and frequency are inversely proportional

** meaning that if wavelength decreases then frequency increases & vice versa.

#1 EXAMPLE PROBLEM:

What is the frequency of light that has a wavelength of 450 nm?

hint: convert nm to m (1m = 1 x 109 nm)

#2 EXAMPLE PROBLEM:

What is the wavelength of electromagnetic radiation if its frequency is 4.5 x 10-3

Hz?

EXIT QUESTION: 5 POINTS

Write down 3 things that you learned today.

Write down one thing you don’t understand.

PARTICLE DESCRIPTION OF LIGHT

1900's experiments showed that light behaved like a stream of extremely tiny, fast moving particles.

EVIDENCE THAT SUPPORTS PARTICLE BEHAVIOR

1) photoelectric effect - refers to the emission of electrons from a metal when light shines on the metal (but only if the frequency was at a certain minimum)

ex/ solar powered items work if you have enough light

MORE EVIDENCE FOR PARTICLE BEHAVIOR

2) Max Planck - studied light emitted from hot metal objects

(like a hot horseshoe glows).

He suggests that objects emit energy in small specific amounts called quanta.

Quantum - minimum quantity of energy that can be lost or gained by an atom To calculate the energy of a quantum of light use formula:

E = hv Where: E = energy (in Joules units)h = 6.626 x 10-34Js (Joule seconds) Planck's

constant v = frequency

ALBERT EINSTEIN (1905)

Introduces the wave-particle dual nature of light.

wave & particle behavioreach particle carries a quantum of

energy. EM radiation is absorbed by matter

in whole numbers of photons.

photon - particle of light (EM radiation) having zero mass and carrying a quantum of energy.

Ephoton = hv

EXAMPLE PROBLEM:

Using: Ephoton = hv

Calculate the frequency for a photon of light that has an energy 3.2 x 10-19 J.

HYDROGEN’S LINE EMISSION SPECTRUMNiels Bohr passed electric current through

hydrogen gasPINK colored light emittedWhen energy is added to an atom,electrons become excited& move to higher energy level.

A photon is emitted when the electrons move back to a more stable, GROUND state.

Ground state – lowest energy state of an atom

Excited state – state in which an atom has a higher potential energy than its ground state.

Ephoton= E2 – E1 = hv

Ephoton= E2 – E1 = hv

The energy of this photon is equal to the difference in energy between the atom’s initial state and its final state.

BOHR MODEL OF THE HYDROGEN ATOM 1913

Bohr links the photon emission of hydrogen to a model of the atom’s electron. See p. 129

Electron circles in orbits (defined paths)Electron has a fixed energyEach concentric circle orbit had an empty

space in between where the electron could not exist (ladder analogy p. 129)

Explanation of the spectral lines produced by hydrogen:

An electron cannot gain or lose energy.

It can move to a higher energy orbit by gaining an amount of energy equal to the difference in final and initial states.

LOUIS DE BROGLIE (“DE BROYLEE”) 1924

He proposed an equation that suggested that any matter with mass and velocity has a corresponding wavelength.

Setting both energy equations equal to each other:

E = mc2 E=hv mc2 = hv (substitute v with wavelength from c = λv)

Wavelength(λ) = h/mc

WERNER HEISENBERG 1927

e- s are detected by their interaction with photons.

This interaction will change both the direction and position of the e-.

Heisenberg uncertainty principle States: It is impossible to determine

simultaneously both position and velocity of an e-

Heisenberg uncertainty principle States: It is impossible to

determine simultaneously both position and velocity of an e-

Therefore, e- s are located in orbitals or 3-D clouds of probable location

(not neat orbits like Bohr’s model nor Rutherford’s planetary model)

Erwin Schrodinger came up with an equation that treated electrons in atoms as waves.

Quantization of electron energies was an outcome of his equation (vs. Bohr’s theory that assumed quantization as a fact)

SEC 1

1. For electromagnetic radiation, c (speed of light) equals _________________________.

2. A quantum of electromagnetic energy is called _______________.

3. The energy of a photon is related to its _____________.

4. If electrons in an atom have the lowest possible energies, the atom is in the ________________.

5. Bohr’s theory helped explain why excited hydrogen gas gives off certain ___________ of light.

6. According to Bohr’s theory, an excited atom would _______________ energy.

SECTION 2 REVIEW Q’S

1. A three-dimensional region around a nucleus where an electron may be found is called a(n) ____________.

2. Unlike in an orbit, in an orbital an electron’s position cannot be known _______________.

3. What are the 4 quantum numbers and what do they represent?

4. What are the shapes of the orbitals?5. How many electrons fit in each orbital?6. What is the difference between a 2s orbital

and a 4s orbital?

SEC 2

1. How many orbital shapes are possible at the 2nd energy level? 3rd energy level?

2. An electron for which n= 5 has more _____ than an electron for which n=3.

3. If 8 electrons completely fill a main energy level, what is n?

SECTION 3 REVIEW Q’S

1. Draw the diagonal rule. What does this rule show?

2. Know the 3 rules for writing electron configurtions.

3. Write the electron configuration for Si.4. Draw the orbital diagram for Mg.5. What element has the following

configuration: 1s22s22p63s1 ?6. How many electrons in the highest energy

level of a bromine atom?7. Which element has the electron

configuration of [Ar]4s23d104p5