Transcript Chapter 2 Atoms and Elements

Chapter 3 Electronic Structure and
the Periodic Law
3.2
Electronic Arrangements in Atoms
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
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Bohr Model or the Solar
Niels Bohr (1885-1962)
System Model
Bohr Model or the Solar System Model
 Niels
Bohr in 1913 introduced his model of the
hydrogen atom.
 Electrons circle the nucleus in orbits, which are
also called energy levels.
 An electron can “jump” from a lower energy level
to a higher one upon absorbing energy, creating
an excited state.
 The concept of energy levels accounts for the
emission of distinct wavelengths of
electromagnetic radiation during flame tests.
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Bohr’s Orbit Model
Definitions
Quantum is the smallest increment of energy, for example, in an atom
emitting or absorbing radiation.
Ground state is the condition of an atom in which all electrons are in their
normal, lowest energy levels.
Excited state is an unstable, higher energy state of an atom.
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Bohr’s Orbit Model (continued)

The Atomic Orbital Model
 Orbits are replaced with atomic orbitals,
volumes of space where the electrons
can be found.
 The arrangement of electrons in the
orbitals is the electronic configuration of
an atom, which determines the
chemistry of an atom.
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Definitions
Electrons in the highest occupied energy level are the greatest
stable distance from the nucleus. These outermost electrons
are known as valence electrons to be discussed in section 3.3.
Shell is a principal energy level defined by a given value of n,
where n can be 1,2,3,4 etc… and is capable of holding 2n2
electrons.
An orbital is a region of three-dimensional space around an
atom within which there is a significant probability (usually
shown as 90%) that a given electron will be found.
Subshells have different energy levels (orbitals) within a given
shell that is designed by a letter from the group s,p,d,& f
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Energy Levels
Energy levels
• are assigned numbers n =
1, 2, 3, 4 and so on.
• increase in energy as the
value of n increases.
• are like the rungs of a
ladder with the lower
energy levels nearer the
ground.
n=4
n=3
n=2
n=1
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Energy levels are spaced differently,
like ladder rungs
Credit: Foto-Search.com
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Atomic energy
levels are like floors of a house
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State transitions for hydrogen
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Energy Levels
Energy levels have a maximum number of electrons
equal to 2n2.
Energy level
n=1
n=2
n=3
Maximum number of electrons
2(1)2 = 2(1) = 2
2(2)2 = 2(4) = 8
2(3)2 = 2(9) = 18
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Orbitals
An orbital
• is a three-dimensional space around a nucleus
where an electron is most likely to be found.
• has a shape that represents electron density (not
a path the electron follows).
• can hold up to 2 electrons.
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s Orbitals
An s orbital
• has a spherical shape
around the nucleus.
• is found in each energy
level.
n=3
n=2
n=1
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
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p Orbitals
A p orbital
• has a two-lobed shape.
• is one of three p orbitals in each energy level from n = 2.
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
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Atomic Orbitals.
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Electrons in Energy Levels n = 1- 4
Energy
Level
1
2
3
4
Orbitals
1s
2s
2p
3s
3p
3d
4s
4p
4d
4f
Maximum
No. of Electrons
2
2
6
2
6
10
2
6
10
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Total
Electrons
2
8
18
32
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Learning Check
The number of
A. electrons that can occupy a p orbital is
1) 1.
2) 2.
3) 3.
B. p orbitals in the 2p sublevel is
1) 1.
2) 2.
3) 3.
C. electrons in the n =3 level
1) 3.
2) 6.
3) 18.
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Solution
The number of
A. electrons that can occupy a p orbital is
2) 2.
B. p orbitals in the 2p sublevel is
3) 3.
C. electrons in the n =3 level
3) 18.
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