Transcript Chapter 4 Arrangements of Electrons in Atoms

Chapter 4
Arrangement of Electrons in
Atoms
Electromagnetic Spectrum
Photoelectric Effect
Quantization of Energy
Energy of a Photon
Absorption and Emission Spectra
Bohr Model of the Atom
Electron Cloud
Quantum Theory
- describes mathematically the wave properties of electrons.
Definitions:
orbital:
three-dimensional region around the nucleus
that indicates the probable location of an
electron. (Each can hold a maximum of 2
electrons.)
ground state: lowest energy state electrons in an atom have.
excited state:
state in which electrons in an atom have
a higher energy than ground state.
Quantum Numbers
Specify the properties of atomic orbitals and the properties
of electrons in orbitals.
Symbol
Description
Principal Quantum #
n
main energy level occupied
by an electron
Angular momentum #
l
shape of orbital in a
particular sublevel
Magnetic Quantum #
m
orientation of orbital
around nucleus
Spin Quantum #
s
direction of spin of electron
Energy Levels and Sublevels
- each principal energy level (n) has one or more sublevels.
-the number of sublevels is the same as the principal
quantum number
First Principal Energy Level (n=1) has 1 sublevel
Second Principal Energy Level (n=2) has 2 sublevels
Third Principal Energy Level (n=3) has 3 sublevels
Each electron in a given sublevel has the same energy
Sublevels continued…
Sublevels are named using letters:
- the first sublevel is called s
- the second sublevel is called p
- the third sublevel is called d
- the fourth sublevel is called f
and so on (g, h …..)
If n=1, how many sublevels are there and what are they
called?
Answer: 1 sublevel called s
If n=2, how many sublevels are there and what are they
called?
Answer: 2 sublevels called s and p
Orbitals
Each sublevel contains 1 or more orbitals
s - sublevel has 1 orbital
p - sublevel has 3 orbitals
d - sublevel has 5 orbitals
f - sublevel has 7 orbitals
Remember each orbital contains a maximum of 2 electrons.
The maximum number of electrons per sublevel:
s→ 2
p→ 6
d → 10
f → 14
More Orbitals
Angular Momentum and Magnetic Quantum Numbers
Quantum Numbers and Orbitals
Shapes of s, p, and d Orbitals
Electrons in Energy Levels and Sublevels
Principal
Energy
Level
(n)
1
2
3
4
Sublevels
available
# of orbitals
in sublevel
# of electrons Total electrons
possible in
for energy level
sublevel
(2n2)
(n)
(n2)
s
s
1
1
2
2
p
s
p
3
1
3
6
2
6
d
s
p
d
f
5
1
3
5
7
10
2
6
10
14
2
8
18
32
Electron Configurations
- shows the arrangement of electrons in an atom
- there are 3 different ways to show electron configurations:
1. Orbital notation
2. Electron-configuration notation
3. Noble gas notation
- electrons are in the ground state unless otherwise noted.
-unfortunately, there is energy overlap beginning at n = 3.
- How can we predict the sublevel order if this occurs?
Aufbau Principle
- electrons occupy the lowest energy levels first.
1s
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d 6f
7s 7p 7d 7f
Hund’s Rule
- Before a second electron can be placed in any orbital,
all the orbitals of that sublevel must contain at least one
electron.
Pauli Exclusion Principle
- In order for two electrons to occupy the same orbital
they must have opposite spin.
- Relates to the Spin Quantum Number (s = +1/2 or -1/2)
- Electrons spin clockwise or counterclockwise.
Orbital Notation
-When illustrating orbital notation for an element:
1. Boxes are used to represent orbitals
2. Each box is labeled with principal energy level
and sublevel.
3. Arrows are used to represent electrons.
Examples
Hydrogen
↑
1s
Lithium
↑↓
↑
1s
2s
Aluminum
↑↓
1s
↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑
2s
2p
3s
3p
Electron Configuration Notation
-When writing electron configurations for an element:
1. Boxes are not used.
2. The principal energy level is written, followed
by the sublevel.
3. The total number of electrons are superscripted
on each sublevel.
Examples
Helium
Sodium
1s2
1s2 2s2 2p6 3s1
Bromine
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5
Noble Gas Notation
-Noble gas notation may be used for elements beginning
with period 3:
1. Find the period the element in question is in.
2. Locate the closest noble gas (must have fewer
electrons than the element in question).
3. Write the symbol of the noble gas in brackets
(This represents ‘x’ number of electrons).
4. Continue the notation with the principal energy
level of the period the element is located in.
Examples
Chlorine
[Ne]3s2 3p5
Iron
[Ar]4s2 3d6
Iodine
[Kr]5s2 4d10 5p5
Noble-Gas Notation
Blocks of the Periodic Table
- The periodic table can be used to predict the order in which
electrons enter sublevels.
Valence Electrons
- Electrons that are located in the highest principal energy
level.
- The maximum number of valence electrons and element
can have is eight.
- Usually valence electrons are found only in s and p
sublevels.
- Electrons that are not valence electrons are inner-shell
electrons.
Examples
Chlorine
[Ne]3s2 3p5
Iron
[Ar]4s2 3d6
Bromine
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5