The Life and Times of Atom

The Life and Times of Atom

A story of one atom’s coming of age

A story of one atom’s coming of age

BIRTHBIRTH

» 1809 - Dalton: pictured the atom as a tiny indestructible sphere

Atom’s baby picture

» 1809 - Dalton: pictured the atom as a tiny indestructible sphere

Atom’s baby picture

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Early Childhood (The awkward years)

1897-Thomson: discovered very light weight negatively charged particles (electrons)

Chemists determined that the negative charge must be balanced by a positive charge: the raisin bun model

Early Adolescence

1911 -Rutherford (McGill University) - publishes the results from the famous gold-foil experiment

The Gold-Foil ExperimentThe Gold-Foil Experiment

Shocking Results!!!Shocking Results!!!

Until this point, atoms were thought to be solid throughout

Most of the alpha particles went right through the foil!

Some alpha particles curved when they went through

Only a few alpha particles deflected back (This was the expected result - think of running into a solid wall)

Until this point, atoms were thought to be solid throughout

Most of the alpha particles went right through the foil!

Some alpha particles curved when they went through

Only a few alpha particles deflected back (This was the expected result - think of running into a solid wall)

Gold Foil ConclusionsGold Foil Conclusions The atom is made up of

mostly empty space Alpha particles are

positive, they curved if they got too close to the small nucleus

Only alpha particles that hit the nucleus were deflected back, since this rarely happened, the nucleus must be very small!

The atom is made up of mostly empty space

Alpha particles are positive, they curved if they got too close to the small nucleus

Only alpha particles that hit the nucleus were deflected back, since this rarely happened, the nucleus must be very small!

Atom’s Troubled Teen-aged Years

Atom’s Troubled Teen-aged Years

An entirely positive nucleus would explode (+ charges repel)

The total mass of the atom couldn’t be accounted for

1932 - Atom gets a girlfriend! The neutron is discovered

An entirely positive nucleus would explode (+ charges repel)

The total mass of the atom couldn’t be accounted for

1932 - Atom gets a girlfriend! The neutron is discovered

Rutherford’s Model of the AtomRutherford’s Model of the Atom

The nucleus is small and made up of protons and neutrons

The electrons circle around the nucleus

The nucleus is small and made up of protons and neutrons

The electrons circle around the nucleus

Problems in Paradise??? Rutherford’s model doesn’t quite

work:Electrons should lose energy and

crash into the nucleus (this clearly doesn’t happen)

19th century physics dictates that a body in motion must continuously give off energy - seen as a continuous spectrum through a spectroscope - but we see a line spectrum

Bohr’s Addition to the Atom

1913 - Bohr explains why a line spectrum is seen instead of a continuous spectrum

Electrons are only giving off certain frequencies of light

Electrons travel in defined spaces called orbitals, which have a defined energy

How does a line spectrum tell us all that?

When an electron is excited (given energy) it jumps from one orbital to a higher orbitalThe electron does not stay excited and eventually goes back to its ground state (original orbital) A wave of light is emitted (photon) from this process which can be seen as a line on a line spectrum

Problems with Bohr’s Theory

Problems with Bohr’s Theory

Bohr couldn’t explain why lines appeared in ones, threes, fives and sevens - more on this later!

Physicist Max Planck supported Bohr’s idea that atoms can absorb or emit only discrete quantities of energy called quantums

Einstein called these ‘packets’ of energy photons

Bohr couldn’t explain why lines appeared in ones, threes, fives and sevens - more on this later!

Physicist Max Planck supported Bohr’s idea that atoms can absorb or emit only discrete quantities of energy called quantums

Einstein called these ‘packets’ of energy photons

AdulthoodAdulthood1926 - Schrodinger - derived the

quantum mechanical model of the atomDescribed electrons as having wave-like

propertiesMathematically determined the shape of

orbitals and the probability of an electron being in a certain place at a certain time - orbitals are not just spheres anymore!

1927 - Heisenburg - Heisenburg Uncertainty Principle: Although the shape of the orbital is predictable, the exact location of an e- can not be determined

1926 - Schrodinger - derived the quantum mechanical model of the atom

Described electrons as having wave-like properties

Mathematically determined the shape of orbitals and the probability of an electron being in a certain place at a certain time - orbitals are not just spheres anymore!

1927 - Heisenburg - Heisenburg Uncertainty Principle: Although the shape of the orbital is predictable, the exact location of an e- can not be determined

Atom’s Portrait 1927

The Four Quantum Numbers (which are actually letters)

The Four Quantum Numbers (which are actually letters)

Why Use Quantum Theory?

Why Use Quantum Theory?

Quantum is the ‘new and improved’ Bohr-Rutherford diagram

This model shows e- placement which helps us determine valence e- and stability of an atom, this allows us to predict atom behaviour

Each orbital can hold a maximum of 2e-

Quantum is the ‘new and improved’ Bohr-Rutherford diagram

This model shows e- placement which helps us determine valence e- and stability of an atom, this allows us to predict atom behaviour

Each orbital can hold a maximum of 2e-

Orbital Shapes & Orientation

s is a sphere shape

- 1 orientation = 1 orbital = 2e-

p is a figure eight

- 3 orientations = 3 orbitals = 6e-

d orbitals have a ‘flower’ shape

- 5 orientations = 5 orbitals = 10 e-

f orbitals have many shapes

- 7orientations in = 7 orbitals = 14 e-

Rules for QuantumRules for Quantum

1. Aufbau Principle - each e- is added into the subshell with the lowest E orbital available

2. Hund’s Rule - Each orbital subshell gets a single electron first and then e- can pair. All e- are ‘up’ when single

3. Pauli Exclusion Principle - no e- can have the same 4 quantum #s in an atom - e- sharing an orbital have opposite spins

1. Aufbau Principle - each e- is added into the subshell with the lowest E orbital available

2. Hund’s Rule - Each orbital subshell gets a single electron first and then e- can pair. All e- are ‘up’ when single

3. Pauli Exclusion Principle - no e- can have the same 4 quantum #s in an atom - e- sharing an orbital have opposite spins