More on the Atomic Model

• B/t Rutherford’s & Bohr’s models: it was hypothesized that electrons orbited the nucleus, just not in a fixed orbit

• The problem: if the orbitals aren’t fixed then the electrons will just fall into the nucleus because + and – attract

• Bohr proposed fixed orbits to fix that problem

More on the Atomic Model

• Quantum mechanics: explains how particles behave (on very tiny scales)

• This is in contrast to classical mechanics used to explain how everyday objects work

• Key idea of QM proposed by Louis de Broglie: matter behaves as particles & waves (wave-particle duality)

De Broglie’s Atom

Heisenberg & Schrödinger

• The key contributors to the current electron cloud model of the atom (among others who contributed to QM such as Planck, Einstein, de Broglie) – Heisenberg’s uncertainty principle: can’t precisely

know position & momentum at the same time– Schrödinger’s wave equation: calculates the

probability of the location of a particle

Schrödinger’s Cat

• Schrodinger was confuzzled by the QM notion of superposition proposed by Einstein & co.

• Superposition: a particle simultaneously exists in all its possible states until observed or interacts with the external world – E.g. e- has both up and down spin states until

observed • Proposed a thought experiment to

demonstrate how ridiculous superposition was

Schrödinger’s Cat

• Cat in box• Box has container filled w/ HCN (poison)• HCN triggered by decay of radioactive

substance• Amount of substance is so tiny that over an

hour 1 atom may decay (w/ equal chance of not decaying)

Schrödinger’s Cat

Schrödinger’s Cat

• Possible states of the radioactive substance: decayed and not decayed…and as a result the cat will be dead and not dead

• Superposition states that these states simultaneously exist until observed

• So until the box is opened, cat is alive and dead (“living & dead cat mixed or smeared out in equal parts” in Schrödinger’s words)

Atomic Structure

Atomic Structure

Location Charge mass (AMU) Mass (kg)

Proton In nucleus +1 (positive) ~1 1.67262178 x 10-27

Neutron In nucleus 0 (neutral) ~1 1.6749 x 10-27

Electron In orbitals outside of

the nucleus -1 (negative) ~0 9.10938291 x 10-31

Elementary Particles

The Higgs Boson

• Can explain why certain particles have mass while others do not

• Can explain how mass is generated, how the universe came to be massive

• Existence confirmed at the Large Hadron Collider (LHC)

Large Hadron Collider

Key Terms

• Atomic number = # of protons (determines what the element is!)

• Mass number = # of protons + neutrons (not the same mass as the one on the periodic table)

• Charge = difference b/t protons & electrons– e.g. if there are 10 protons and 11 electrons…Charge = 10(+1) + 11(-1) = 10 - 11 = -1

• Ions: atoms or molecules with a charge– Cations: + ions– Anions: - ions

Nuclear Notation

• Try writing the following in nuclear notation:Nitrogen atom, Cl-, Mg2+, carbon-14

Isotopes

• Isotopes of an element have different # of neutrons and therefore masses

• E.g. Carbon-12 is the most common isotope of carbon on earth. C-13 (13C) and C-14 (14C) are other isotopes.

• Atomic mass (on the periodic table) is a weighted average of all the isotopes of an element using their % abundance

Remember Carbon Dating?

• Radioactive 14C is made in the atmosphere• Combines w/ O2 to make CO2

• CO2 taken in by plants for photosynthesis

• Animals eat plants & acquire radiocarbon until they die at which point they stop acquiring 14C and it undergoes radioactive decay

• Can be used to measure up to 50,000 years in the past (14C half-life ~5730 years)

Calculating Atomic Mass

• E.g. calculate the molar mass of carbon given the following table

Calculating Atomic Mass

12.000000 x 0.9893 + 13.003355 x .0107 = 11.8716 + 0.1391358985= 12.0107359= 12.01

PhET Simulations

1) Hydrogen Atom2) Rutherford Scattering3) Isotope 4) Build an AtomPlay around, visualize what you’ve learned.#4 make sure you do the quiz!

HW for Tomorrow

• On the website

• Print it out, copy it out or email it