Week of Monday November 13th, 2006

The atom

Rutherford’s Problem

Niels Bohr’s Solution

Monday November 13th, 2006

The atomRutherford’s Problem

Niels Bohr’s Atomic ModelBohr’s Problem

Heisenberg’s Uncertainty Principle

Drill

• Why don’t the nuclei of the atoms in your bottom touch the nuclei of atoms in the chair when you sit down?

• Atomic # number means the # of ______ and when the atom is neutral, the atomic # will be the same as the # of _________.

• Convert units:– 500 mL to ____________pL 13L = 13,000 ____– 17 ms to ____________Ms 0.1m = 100

_____– 3,001 mm to _______m 0.1 cm = 1 _____

500,000,000,0005 x 1011

0.000 000 0171.7 x 10-8

3.001

mL

mmmm

protons

electrons

Electrons repel each other.

Subatomic particles

• Protons

• Neutrons

• ElectronsAll mass is in the nucleus

Mass = 1/2000th of The mass of neutronsOr protons.

The world of the electron

• Electrons move about the nucleus (protons & neutrons)

• Electrons are exceedingly tiny– Rules are different for them– They live in the world of quantum mechanics

• The line separating matter from energy blurs

Rutherford’s problem

Rutherford thought:• Nucleus is positive

(protons & neutrons)

• Electrons are negative

• Electrons orbit around nucleus like planets around the sun

Questions that remain:1. How do electrons manage

to stay apart from nucleus (opposites attract)?

2. When you add energy to atoms, why do they give off light?

Niels Bohr’s Solution

1. Electrons can stay separate from nucleus if:

• Electrons have their own energy that keeps them from getting sucked into nucleus

Bohr tries to prove this by:• Predicting how much energy

that is for each electron– Kinetic energy of each

electron = KE = ½mv2

• Finding how far away those orbits are from nucleusThey should orbit at very

specific distances away from the nucleus for model to be stable

1885 - 1962

Bohr’s model of the atom

nucleus

Electron orbitals/energy levels

Electron loses energy as it falls down an energy levelhv is wavelength of light given off

Lower energy Levels are closer to nucleus.

Higher energy Levels are farther from nucleus.

Niels Bohr’s Solution

2. Atoms give off light when they absorb energy because:

• Each orbital = an energy level

• Electrons can jump energy levels when energy is added to an atom

• Electrons give off energy (light) when source of energy is taken away

• Light wavelength depends on how far electrons fall

1885 - 1962

Bohr’s problem

• Could not measure how fast electrons moved without losing their location.

• Could not pinpoint electron location without losing information on their velocity.

Schrödinger’s theory

• Thinks Bohr is wrong:– Electrons aren’t really matter, but waves of

energy

Heisenberg’s Uncertainty Principle

Quantum mechanics– Impossible to know both location &

velocity of electron because observation involves using light.

• Light will change location and velocity of electron because it adds energy!

– What you can know is the probability of electron’s location & velocity

– Electron orbital now area where electron has a probability of being found

– Answers the particle/wave argument

Atom in its neutral state

• # protons

• This is the way elements are shown in the PT

= atomic # = # electrons

Normal (on earth) chemical rxns

Atoms Δ # of electrons by– Stealing– Losing– Sharing

with other atoms

Δ means “change”

Nuclear Chemistry

• If you Δ what is in the nucleus you are doing nuclear chemistry– Δ # protons you have a new element– Δ # neutrons radioactive decay

Δ means “change”

Where do elements come from?

While you are watching movie, write down no more than 4 words for each question.

HW for tonight

Rewrite your answers in complete sentences.

Niels Bohr