Electronic Configurations of Atoms

Electronic Configurations of Atoms

The Development of Atomic Models


What was inadequate about Rutherford’s atomic model?

5.1


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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The Bohr Model

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

5.1

The Bohr Model

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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The Bohr Model

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


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

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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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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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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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Atomic Orbitals

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

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Atomic Orbitals

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

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Atomic Orbitals

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

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Atomic Orbitals

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

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Electron Configurations

• Electron Configurations– What are the three rules for writing the

electron configurations of elements?

5.2


• The ways in which electrons are arranged in various orbitals around the nuclei of atoms are called electron configurations.

– Three rules—the aufbau principle, the Pauli exclusion principle, and Hund’s rule—tell you how to find the electron configurations of atoms.

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– Aufbau Principle• According to the aufbau principle, electrons

occupy the orbitals of lowest energy first. In the aufbau diagram below, each box represents an atomic orbital.

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– Pauli Exclusion Principle• According to the Pauli exclusion principle, an

atomic orbital may describe at most two electrons. To occupy the same orbital, two electrons must have opposite spins; that is, the electron spins must be paired.

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– Hund’s Rule• Hund’s rule states that electrons occupy orbitals

of the same energy in a way that makes the number of electrons with the same spin direction as large as possible.

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• Orbital Filling Diagram

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– Simulation 2 – Fill atomic orbitals to build the ground state of

several atoms.

for Conceptual Problem 1.1

Problem Solving 5.9 Solve Problem 9 with the help of an interactive guided tutorial.

Exceptional Electron Configurations

• Exceptional Electron Configurations– Why do actual electron configurations for

some elements differ from those assigned using the aufbau principle?

5.2

Exceptional Electron Configurations

– Some actual electron configurations differ from those assigned using the aufbau principle because half-filled sublevels are not as stable as filled sublevels, but they are more stable than other configurations.

5.2

Exceptional Electron Configurations• Exceptions to the aufbau

principle are due to subtle electron-electron interactions in orbitals with very similar energies.

• Copper has an electron configuration that is an exception to the aufbau principle.

5.2

5.2 Section Quiz.

• 5.2.

5.2 Section Quiz.

– 1. Identify the element that corresponds to the following electron configuration: 1s22s22p5.

• F• Cl• Ne• O

5.2 Section Quiz.– 2. Write the electron configuration for the

atom N.• 1s22s22p5

• 1s22s22p3

• 1s22s1p2

• 1s22s22p1

`

– 3. The electron configurations for some elements differ from those predicted by the aufbau principle because the

• the lowest energy level is completely filled.

• none of the energy levels are completely filled.

• half-filled sublevels are less stable than filled energy levels.

• half-filled sublevels are more stable than some other arrangements.

5.2 Section Quiz.

chemistry

Physics and the Quantum Mechanical Model

• Neon advertising signs are formed from glass tubes bent in various shapes. An electric current passing through the gas in each glass tube makes the gas glow with its own characteristic color. You will learn why each gas glows with a specific color of light.

5.3

Light

• Light– How are the wavelength and frequency of

light related?

5.3

Light

– The amplitude of a wave is the wave’s height from zero to the crest.

– The wavelength, represented by (the Greek letter lambda), is the distance between the crests.

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Light

– The frequency, represented by (the Greek letter nu), is the number of wave cycles to pass a given point per unit of time.

– The SI unit of cycles per second is called a hertz (Hz).

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Light

– The wavelength and frequency of light are inversely proportional to each other.

5.3

Light

• The product of the frequency and wavelength always equals a constant (c), the speed of light.

5.3

Light

• According to the wave model, light consists of electromagnetic waves.

– Electromagnetic radiation includes radio waves, microwaves, infrared waves, visible light, ultraviolet waves, X-rays, and gamma rays.

– All electromagnetic waves travel in a vacuum at a speed of 2.998 108 m/s.

5.3

Light

• Sunlight consists of light with a continuous range of wavelengths and frequencies.

– When sunlight passes through a prism, the different frequencies separate into a spectrum of colors.

– In the visible spectrum, red light has the longest wavelength and the lowest frequency.

5.3

Light

• The electromagnetic spectrum consists of radiation over a broad band of wavelengths.

5.3

Light

– Simulation 3 – Explore the properties of electromagnetic

radiation.

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for Sample Problem 5.1

Problem-Solving 5.15 Solve Problem 15 with the help of an interactive guided tutorial.

Atomic Spectra

• Atomic Spectra– What causes atomic emission spectra?

5.3

Atomic Spectra

– When atoms absorb energy, electrons move into higher energy levels. These electrons then lose energy by emitting light when they return to lower energy levels.

5.3

Atomic Spectra• A prism separates light into the colors it contains. When

white light passes through a prism, it produces a rainbow of colors.

5.3

Atomic Spectra

• When light from a helium lamp passes through a prism, discrete lines are produced.

5.3

Atomic Spectra• The frequencies of light emitted by an element

separate into discrete lines to give the atomic emission spectrum of the element.

5.3

Mercury Nitrogen

An Explanation of Atomic Spectra

• An Explanation of Atomic Spectra– How are the frequencies of light an atom

emits related to changes of electron energies?

5.3


• In the Bohr model, the lone electron in the hydrogen atom can have only certain specific energies.

– When the electron has its lowest possible energy, the atom is in its ground state.

– Excitation of the electron by absorbing energy raises the atom from the ground state to an excited state.

– A quantum of energy in the form of light is emitted when the electron drops back to a lower energy level.

5.3


– The light emitted by an electron moving from a higher to a lower energy level has a frequency directly proportional to the energy change of the electron.

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• The three groups of lines in the hydrogen spectrum correspond to the transition of electrons from higher energy levels to lower energy levels.

5.3


– Animation 6 – Learn about atomic emission spectra and how

neon lights work.

Quantum Mechanics

• Quantum Mechanics– How does quantum mechanics differ from

classical mechanics?

5.3

Quantum Mechanics

• In 1905, Albert Einstein successfully explained experimental data by proposing that light could be described as quanta of energy.

– The quanta behave as if they were particles.– Light quanta are called photons.

5.3

The Planck Equation

The energy of electromagnetic radiation is directly related to the frequency

E = hh is the Planck constant = 6.626 x 10-34 J.s

is the frequency in Hz

END OF SHOW

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Electronic Configurations of Atoms