Transcript atomic orbital

Chemistry
Wilbraham
Staley
Matta
Waterman
Chapter 5: Electrons in Atoms
Copyright © 2005 Pearson Education & Prentice-Hall, Inc.
How do we make
fireworks?
Fireworks!
The brilliant colors of
fireworks are produced by
using compounds
containing different
elements. In this chapter,
you will learn how elements
can emit light of different
colors.
The chemistry of Fireworks
http://www.youtube.com/watch?v=OKklDcS3FsA&feature=pla
yer_embedded
5.1 Revising the Atomic Model
Energy levels in Atoms
We know atoms consist of protons and neutron making up
the nucleus surrounded by electrons.
Limitations of Rutherford’s
Atomic Model
What were the limitations?
Limitations of Rutherford’s
Atomic Model
Explained a few simple properties of atoms.
Could not explain the chemical properties of
elements.
Could not explain why metals or compounds of
metals give off characteristic colors when heated
in a flame.
Could not explain why an object such as iron
heated first glows dull red, then yellow, then white
when heated to higher and higher temperatures.
The Bohr Model
In 1913, Niels Bohr, a Danish
physicist and a student of
Rutherford, developed a new atomic
model.
Incorporated newer discoveries
about how the energy of an atom
changes when the atom absorbs or
emits light.
He considered the simplest atom,
hydrogen, which has one electron.
Bohr proposed that an electron is
found only in specific circular
paths, or orbits, around the
nucleus.
Key points of Bohr’s model
Each possible electron orbit has a
fixed energy.
The fixed energies an electron can
have are called energy levels.
Think of these like the rungs of a
ladder.
Rungs of ladders
The lowest rung of the ladder
corresponds to the lower
energy.
A person can climb up or
down the ladder by stepping
from rung to rung.
Similarly, an electron can
move from one energy level to
another.
To move up
A person on the ladder cannot stand
between rungs.
Similarly, the electrons in an atom
cannot exist between energy levels.
To move from one rung to another, a
person climbing the ladder must
move just the right distance.
To move from one energy to
another, an electron must gain or
lost just the right amount of energy.
A quantum of energy is the amount of energy required to
move an electron from one energy level to another energy
level.
The word quantity has the same root as quantum and means
“a definite amount or number”.
The energy of an electron is therefore said to be quantized.
The amount of energy an electron gains or losses in an atom
is not always the same.
Energy levels
The rungs of a ladder are
somewhat like the energy
levels of Bohr’s model of the
atom. In an ordinary ladder, the
rungs are equally spaced.
The energy levels in atoms are
unequally spaced, like the
rungs in this unusual ladders.
The higher energy levels are
closer together.
The energy levels in an
atom are not equally
spaced. The higher energy
levels are closer together.
It takes less energy to
climb from one rung to
another near the top of the
ladder.
Bohr fail to explain the energies absorbed and emitted by
atoms with more than one electron.
The Quantum Mechanical model
The modern description of the
electrons in atoms, the
quantum mechanical model,
came from the mathematical
solutions to the Schrodinger
equation.
The quantum mechanical model
does not specify an exact path the
electron takes 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.
Probability describes how
likely it is to find an electron in
a particular location around
the nucleus of an atom.
Probability demonstration
Describe how electrons move
around the nucleus is similar to a
description of how the blades of a
windmill rotate.
The blurry region they produce in
the picture, but you cannot predict
their exact locations at any instant.
The probability of finding an electron
within a certain volume of space
surrounding the nucleus can be
represented as a fuzzy cloud-like
region.
The cloud is more dense where the
probability of finding the electron is high
less dense where the probability of
finding the electron is low.
No boundary to the cloud because there
is a slight change of finding the electron
at a considerable distance from the
nucleus.
Atomic Orbitals
How do sublevels of principal
energy levels differ?
Atomic Orbitals
Schrodinger equation also leads to a
mathematical expression, called an
atomic orbital.
The atomic orbital, describes the
probability of finding an electron at
various locations around the
nucleus.
pictorial representation shows a
region of space in which there is a
high probability of finding an
electron.
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.
Each energy sublevel
corresponds to one or more
orbitals of different shapes.
The orbitals describe where an
electron is likely to be found.
Denoted by letters.
http://www.slideshare.net/wsautter/elect
ron-configuration-of-atoms
S orbitals are spherical
P orbitals are dumbbell-shaped
Three kinds of p orbitals have
different orientations in space.
Four or five kinds of d orbitals are
in your book on page 131.
Shapes of s and p
orbitals
For a given principal
energy level greater
than 1, there is one s
orbital and three p
orbitals.
Shapes of d orbitals
Four of the five d orbitals
have the same shape but
different orientations.
How are the orientations
of dxy and dx2-y2 orbitals
similar? How are they
different?
d orbitals
Electron Orbitals
Periodic Table
S Orbitals
Each orbital holds 2 electrons.
Left side of the periodic table are the ‘s orbitals’.
P Orbitals
There are 3 sub
orbitals
Each contains 2
electrons
totals electrons = 6
groups 13-18 on the
periodic table are p
orbitals
D Orbitals
There are 5 sub
orbitals.
Each contains 2
electrons.
Total electrons = 10
Groups 3-12 on periodic
table are D orbitals.
F Orbital
There are 5 sub orbitals.
Each orbital contains 2
electron.
Total electrons = 10.
Groups at the very bottom
of the periodic table are F
orbitals.
Sorting Periodic Table into Orbital Types
What type of electrons are in
elements
Electron Configuration
Worksheet for HW
An angular node is a flat plane such as the ones
shown in the diagram above. The ℓ quantum number
determines the number of angular nodes an orbital will
have. A radial node is a circular ring that occurs as
the principle quantum number increases. Thus, n tells
us how many radial nodes an orbital will have and is
calculable with the equation: Total # of nodes = n-1.
Problems
1.
Which orbital would the electrons fill first? The 2s or 2p orbital?
2.
How many d orbitals are there in the d subshell?
3.
How many electrons can the p orbital hold?
4.
Determine the number of angular and radial nodes of a 4f orbital.
5.
What is the shape of an orbital with 4 radial nodes and 1 angular node in the xy plane?
Solutions
1.
2.
3.
4.
5.
The 2s orbital would be filled before the 2p orbital because orbitals that are lower in energy are filled first. The 2s orbital is
lower in energy than the 2p orbital.
There are 5 d orbitals in the d subshell.
A p orbital can hold 6 electrons.
Based off of the given information, n=4 and ℓ=3. Thus, there are 3 angular nodes present. The total number of nodes in
this orbital is: 4-1=3, which means there are no radial nodes present.
1 angular node means ℓ=1 which tells us that we have a p subshell, specifically the pz orbital because the angular node is
on the xy plane. The total number of nodes in this orbital is: 4 radial nodes +1 angular node=5 nodes. To find n, solve the
equation: nodes=n-1; in this case, 5=n-1, so n=6. This gives us a: 6pz orbital
Electron Configuration
http://www.germane-software.com/~dcaley/atom/Atom.html