1. Chapter 5 Electrons In Atoms 5.1 Revising the Atomic Model
5.2 Electron Arrangement in Atoms
5.3 Atomic Emission Spectra and
the Quantum Mechanical Model
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2. Limitations of Rutherford’s Atomic Model
Energy Levels in Atoms
Limitations of Rutherford’s Atomic Model
It explained only a few simple properties of atoms.
It could not explain the chemical properties of elements.
For example, Rutherford’s model could not explain why an object such as the iron scroll shown here first glows dull red, then yellow, and then white when heated to higher and higher temperatures.
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3. Energy Levels in Atoms
The Bohr Model
In 1913, Niels Bohr (1885–1962), a young Danish physicist and a student of Rutherford, developed a new atomic model.
He changed Rutherford’s model to incorporate newer discoveries about how the energy of an atom changes when the atom absorbs or emits light.
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4. Energy Levels in Atoms
The Bohr Model
Bohr proposed that an electron is found only in specific circular paths, or orbits, around the nucleus.
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5. Each possible electron orbit in Bohr’s model has a fixed energy.
Energy Levels in Atoms
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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6. Energy Levels in Atoms
The Bohr Model
The rungs on this ladder are somewhat like the energy levels in Bohr’s model of the atom.
A person on a ladder cannot stand between the rungs. Similarly, the electrons in an atom cannot exist between energy levels.
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7. How does the Bohr model improve upon the Rutherford model?
The Rutherford model could not explain why elements that have been heated to higher and higher temperatures give off different colors of light. The Bohr model explains how the energy levels of electrons in an atom change when the atom emits light.
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8. The Quantum Mechanical Model
Erwin Schrödinger (1887–1961)
Like the Bohr model, the quantum mechanical model of the atom restricts the energy of electrons to certain values.
Unlike the Bohr model, however, the quantum mechanical model does not specify an exact path the electron takes around the nucleus.
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9. 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 of an atom.
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10. The Quantum Mechanical Model
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 cloudlike region.
The cloud is more dense where the probability of finding the electron is high.
Electron cloud
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11. Atomic Orbitals
Solutions to the Schrödinger equation give the energies, or energy levels, an electron can have.
For each energy level, the Schrödinger equation also leads to a mathematical expression, called an atomic orbital.
An atomic orbital is represented pictorially as a region of space in which there is a high probability of finding an electron.
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12. These numbers are assigned the values n = 1, 2, 3, 4, and so forth.
Atomic Orbitals
The energy levels of electrons in the quantum mechanical model are labeled by principal quantum numbers (n).
These numbers are assigned the values n = 1, 2, 3, 4, and so forth.
For each principal energy level greater than 1, there are several orbitals with different shapes and at different energy levels.
These energy levels within a principal energy level constitute energy sublevels.
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13. Atomic Orbitals
Each energy sublevel corresponds to one or more orbitals of different shapes. The orbitals describe where an electron is likely to be found.
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14. Different atomic orbitals are denoted by letters.
The s orbitals are spherical.
The p orbitals are dumbbell-shaped.
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15. Atomic Orbitals
For a given principal energy level greater than 1, there is one s orbital, 3 p orbitals, and 5 d orbitals.
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16. Atomic Orbitals
The numbers and types of atomic orbitals depend on the principal energy level.
Summary of Principal Energy Levels and Sublevels
Principal energy level
Number of sublevels
Type of sublevel
Maximum number of electrons
n = 1 1
1s (1 orbital) 2
n = 2
2s (1 orbital), 2p (3 orbitals) 8
n = 3 3
3s (1 orbital), 3p (3 orbitals),
3d (5 orbitals) 18
n = 4 4
4s (1 orbital), 4p (3 orbitals),
4d (5 orbitals), 4f (7 orbitals) 32
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17. The number of orbitals in a principal energy level is equal to n2.
Atomic Orbitals
The principal quantum number, n, always equals the number of sublevels within that principal energy level.
The number of orbitals in a principal energy level is equal to n2.
A maximum of two electrons can occupy an orbital.
Therefore, the maximum number of electrons that can occupy a principal energy level is given by the formula 2n2.
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18. Calculate the maximum number of electrons in the 5th principal energy level (n = 5).
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19. CHEMISTRY & YOU
Why do scientists no longer use physical models to describe the motion of electrons?
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20. CHEMISTRY & YOU
Why do scientists no longer use physical models to describe the motion of electrons?
Previous models of the atom were physical models based on the motion of large objects.
Theoretical calculations and experimental results showed that these models did not always correctly describe electron motion.
Schrödinger devised a mathematical equation describing the behavior of the electron in a hydrogen atom. The quantum mechanical model came from the solutions to the Schrödinger equation.
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21. Key Concepts
Bohr proposed that an electron is found only in specific circular paths, or orbits, around the nucleus.
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 of an atom.
Each energy sublevel corresponds to one or more orbitals of different shapes, which describe where the electron is likely to be found.
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22. Electron Configurations
Aufbau Principle
Increasing energy 6s 5s 4s 3s 2s 1s 6p 5p 5d 4p 4d 4f 3p 3d 2p
The aufbau diagram shows the relative energy levels of the various atomic orbitals. Orbitals of greater energy are higher on the diagram.
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23. Electron Configurations
Look at the orbital filling diagram of the oxygen atom.
Electron Configurations of Selected Elements
Element 1s 2s
2px 2py 2pz 3s
Electron configuration H
1s1 He
1s2 Li
1s22s1 C
1s22s22p2 N
1s22s22p3 O
1s22s22p4 F
1s22s22p5 Ne
1s22s22p6 Na
1s22s22p63s1
The 1s orbital has two electrons of opposite spin.
The 2s orbital also has two electrons of opposite spin.
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25. Glossary Terms
energy level: the specific energies an electron in an atom or other system can have
quantum: the amount of energy needed to move an electron from one energy level to another
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26. Glossary Terms
quantum mechanical model: the modern description, primarily mathematical, of the behavior of electrons in atoms
atomic orbital: a mathematical expression describing the probability of finding an electron at various locations; usually represented by the region of space around the nucleus where there is a high probability of finding an electron
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