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Plum Pudding ModelJ.J. Thomson

1897

The arrangement of electrons in an atom determine most of the chemical properties of that atom. Electrons are what actually do the reacting.

Ernest RutherfordAtomic Model

1911

Unanswered Questions:1) Why do certain gases emit colors of light when electricity is added?2) Why do metals give off colors when heated?3) Why do atoms for cations and anions?

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Niels Bohr (1885-1962)

Danish physicist who determined that electrons were actually in distinct ENERGY LEVELS and not just on the outer edges of the atom.

Electrons could ONLY be found in these circular paths (orbits) around the nucleus.

Each energy level had a certain amount of energy associated with it. If an electron contained that "quantum" of energy, then it could maintain that space. If it couldn't maintain that "quantum" of energy, then it would fall to a lower energy level.

If it gained energy through some other means, that electron could jump to a higher energy level.

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Ground State= the normal positioning of the electrons

Excited State= electrons have jumped into higher energy levels

Higher EnergyLess StableLeaps occur with smallchanges in energy

Lower EnergyMore StableLeaps occur with large changes in energy

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The fixed energy levels of electrons are somewhat like the rungs of a ladder.

The lowest rung of the ladder corresponds to the lowest energy level and most stable positioning.

A person can climb up or down a ladder by going from rung to rung. Similarly, an electron can jump from one energy level to another.

A person on a ladder cannot stand between the rungs. Similarly, the electrons in an atom cannot be between energy levels.

In general, the higher an electron is on the energy ladder, the farther it is from the nucleus.

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The Bohr Model explained electron behavior for the Hydrogen atom (which has one electron).

It failed in many ways to explain the energies absorbed and emitted by atoms wtih more than one electron.

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Schrodinger developed a mathematical equation that would calculate the probability of locating an electron. These probabilities took the form of different "cloud" regions.

The Quantum Mechanical Model is based on the principle that the position of an electron can NEVER be pinpointed in the same way that a single blade on a spinning propeller can never be pinpointed.

An electron's position can only be given in terms of a probable region of space where it can be located.

1887‐1961Austrian PhysicistNobel Prize in 1933

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What does the Quantum Mechanical Model Tell Us?

Electrons were traveling in cloud‐like regions rather than in orbits around the nucleus.

These cloud regions have a unique shape and size depending upon the energy level.

Numbers are associated with energy levels, sublevels, orbitals, spins, and electrons to be used mathematically in Schrodinger's Equation.

Four Quantum Numbers

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The Quantum Mechanical Model: What are Quantum Numbers?

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The Quantum Mechanical Model: What are Quantum Numbers?

l

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The Quantum Mechanical Model: What are Quantum Numbers?

l

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The Quantum Mechanical Model: What are Quantum Numbers?

l l

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The Quantum Mechanical Model: What are Quantum Numbers?

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If l

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If l

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If l

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If l

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Quantum Number Quick Chart

E.L.n l

orbitals allowedm

# of orbitals

# of electrons

1 0 (s) 0 1 2

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Quantum Number Notation

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These electron arrangements determine the chemical properties of every element.

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