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chemistry

© Copyright Pearson Prentice Hall

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Models of the Atom

The scale model shown is a physical model. However, not all models are physical. In fact, several theoretical models of the atom have been developed over the last few hundred years. You will learn about the currently accepted model of how electrons behave in atoms.

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Models of the Atom >

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The Development of Atomic Models

The Development of Atomic Models

What was inadequate about Rutherford’s atomic model?

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Models of the Atom > The Development of Atomic Models

Rutherford’s atomic model could not explain the chemical properties of elements.

Rutherford’s atomic model could not explain why objects change color when heated.

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The timeline shoes the development of atomic models from 1803 to 1911.

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The timeline shows the development of atomic models from 1913 to 1932.

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The Bohr Model

The Bohr Model

What was the new proposal in the Bohr model of the atom?

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Models of the Atom > The Bohr Model

Bohr proposed that an electron is found only in specific circular paths, or orbits, around the nucleus.

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Each possible electron orbit in Bohr’s model has a fixed energy.

• The fixed energies an electron can have are called energy levels.

• A quantum of energy is the amount of energy required to move an electron from one energy level to another energy level.

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Like the rungs of the strange ladder, the energy levels in an atom are not equally spaced.

The higher the energy level occupied by an electron, the less energy it takes to move from that energy level to the next higher energy level.

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The Quantum Mechanical Model

The Quantum Mechanical Model

What does the quantum mechanical model determine about the electrons in an atom?

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Models of the Atom > The Quantum Mechanical Model

The quantum mechanical model determines the allowed energies an electron can have and how likely it is to find the electron in various locations around the nucleus.

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Austrian physicist Erwin Schrödinger (1887–1961) used new theoretical calculations and results to devise and solve a mathematical equation describing the behavior of the electron in a hydrogen atom.

The modern description of the electrons in atoms, the quantum mechanical model, comes from the mathematical solutions to the Schrödinger equation.

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The propeller blade has the same probability of being anywhere in the blurry region, but you cannot tell its location at any instant. The electron cloud of an atom can be compared to a spinning airplane propeller.

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In the quantum mechanical model, the probability of finding an electron within a certain volume of space surrounding the nucleus can be represented as a fuzzy cloud. The cloud is more dense where the probability of finding the electron is high.

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Atomic Orbitals

Atomic Orbitals

How do sublevels of principal energy levels differ?

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Models of the Atom > Atomic Orbitals

An atomic orbital is often thought of as a region of space in which there is a high probability of finding an electron.

Each energy sublevel corresponds to an orbital of a different shape, which describes where the electron is likely to be found.

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Different atomic orbitals are denoted by letters. The s orbitals are spherical, and p orbitals are dumbbell-shaped.

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Four of the five d orbitals have the same shape but different orientations in space.

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The numbers and kinds of atomic orbitals depend on the energy sublevel.

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The number of electrons allowed in each of the first four energy levels are shown here.

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Animation 5

Observe the characteristics of atomic orbitals.

Atomic Orbitals

5.1 models of the atom -...

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