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Chapter 4:
Arrangement of Electrons in Atoms
by Chris Baldwin, Kayla Cooper, Melissa Thomas, and Taylor Washington
Section 1:
The Development of a New Atomic Model
by Chris Baldwin
The Wave Description of Light
---- Visible light is a type of electromagnetic radiation, a form of energy that
exhibits wavelike behavior as it travels through space
---- Other examples of electromagnetic radiation would be ultraviolet or
infrared
light, microwaves, radio waves, and X rays
---- All forms of electromagnetic radiation travel at a constant speed of about
3.0 * 10^8 meters per second
The Wave Description of Light
---- The motion of waves is very
repetitive, which means that
waves can be categorized by
measureable properties
---- One of these properties is
wavelength, (λ) the distance
between corresponding points on
adjacent waves
---- Another property is frequency, (v)
the number of waves that pass a
given point in a specific time,
usually one second, measured in
waves per second, which is called
a hertz
The Wave Description of Light
---- Frequency and wavelength are mathematically related to each other
---- The relationship between frequency and wavelength is c=λv, with c being
the speed of light, λ being wavelength, and v being frequency
---- The product of λv is always a constant. λis inversely proportional to v. As
wavelength decreases, frequency rises, and vice versa
The Photoelectric Effect
---- The photoelectric effect is
the emission of electrons
from a metal when light
shines on the metal
---- The photoelectric effect
was a phenomenon
because for a given metal,
no electrons were
released if the frequency of
the light was below a
certain measurement
The Particle Description of Light
---- German scientist Max Planck suggested that objects emit energy in small,
specific amounts, called quanta. A quantum is the minimum quantity of
energy that can be lost or gained by an atom
---- Planck also came up with a relationship between a quantum of energy and
the frequency of radiation, represented by E=hv, E being the energy in
joules of a quantum of radiation, v the frequency of the radiation, and h,
Planck’s constant, which is about 6.626 * 10^-34 J*s
---- Einstein expanded on Planck’s ideas by introducing an idea that light could
be thought of as a stream of particles and each particle carries a quantum
of energy
---- These particles were named photons, particles of electromagnetic radiation
having zero mass and carrying a quantum of energy
The Hydrogen-Atom Line-Emission Spectrum
---- The lowest energy state of an atom is its ground state
---- A state where an atom has a higher potential energy than it has in its
ground state is an excited state
---- When an excited atom goes back down to its ground state, energy is given
off in the form of electromagnetic radiation
---- Scientists conducted an experiment where an electric current was passed
through hydrogen, which resulted in the emission of a pinkish glow
---- The line-emission spectrum is when narrow beams of emitted light are shined
through a prism, separating it into specific frequencies of visible light
Bohr Model of the Hydrogen Atom
---- Scientists were puzzled by the
fact
that excited hydrogen atoms
gave off only specific
frequencies of light
---- Niels Bohr solved the dilemma by
creating a model of the
hydrogen atom
Section Questions
Q: What is the difference between wavelength and frequency?
A: Wavelength is the distance between adjacent waves, while frequency is the
number of waves that pass in a specific amount of time.
Q: What is the definition of a quantum?
A: A quantum is the minimum quantity of energy that can be lost or gained by
an atom
Section 2:
The Quantum Model of the Atom
by Kayla Cooper
Electrons As Waves
---- Scientists contradicted Bohr’s model of atoms
---- They believed that electrons could move on an direction and weren’t
confined to an orbital
---- Louis de Broglie suggested that electrons could act like waves
---- Experiments confirmed that electrons could be bent or diffracted and can
interfere when two beams of electrons overlap
The Heisenberg Uncertainty Principle
---- Werner Heisenberg experimented on the movement of electrons
---- Discovered the Heisenberg uncertainty principle which stated that it is
impossible to know the location and velocity of an electron at the same
time because they are always moving
---- This principle was proven to be one of the most fundamental ways of
understanding the concepts of light and matter
The Schrodinger Wave Equation
---- Erwin Schrodinger believed electrons acted as waves
---- Schrodinger’s wave equation and the Heisenberg uncertainty principle led
to the discovery of the quantum theory
---- The quantum theory describes mathematically the wave properties of
electrons and other very small particles
---- Electrons move in orbitals which are three-dimensional regions around the
nucleus that indicate the probable location of an electron
Atomic Orbitals & Quantum Numbers
---- Quantum numbers are used to describe different orbitals
---- Quantum numbers specify the properties of the orbitals and the properties of
the electrons inside of them
---- The principal, angular momentum, magnetic, and spin are the four quantum
numbers
Atomic Orbitals & Quantum Numbers
---- The principal quantum number
which is symbolized by n, indicated
the main energy level occupied by
the electron
---- n is the number of energy levels
and n squared is the number of
orbitals in each energy level
---- As n increases, the energy of the
electron and its average distance
from nucleus heighten
Atomic Orbitals & Quantum Numbers
---- The angular momentum quantum number, symbolized by l, indicates the
shape, or sublevel, of the orbital
---- These orbitals can be either s, p, d, or f
---- The number of orbital shapes possible is equal to the principal quantum
number: if n=1, s is the only orbital present l, if n=2, it can hold both s and p
orbitals, and so on
Atomic Orbitals & Quantum Numbers
---- The magnetic quantum number,
m, states the orientation of orbitals
around the nucleus
---- The s orbital only has one possible
orientation, since it’s a sphere p has
3, and d has 5
Atomic Orbitals & Quantum Numbers
---- The spin quantum number, has 2 possible values, (-1/2 and +1/2), since there
are only 2 ways an electron can spin
---- An orbital can only hold a maximum of 2 electrons, which have to have the
opposite spin
Section Questions
Q: How did Louis de Broglie change the way that we think about electrons?
A: de Broglie was the scientist who suggested that electrons act like waves.
Q: What is a quantum number? State the 4 quantum numbers with a brief
description of each.
A: A quantum number specifies the properties of orbitals and or the properties
of the electrons inside of them. The principal quantum number states the
energy level, the angular momentum quantum number indicates the
sublevel, the magnetic quantum number shows the orientation of orbitals,
and the spin quantum number tells the direction electrons are spinning.
Section 3:
Electron Configurations
Part 1:
Rules and Representation of Electron Configuration
by Taylor Washington
Rules Governing Electron Configurations
---- Electron configuration is the
arrangement of electrons in an
atom
---- Electrons are added to orbitals
according to three basic rules
---- The first rule is the order in which
electrons occupy orbitals, the
Aufbau principle says that an
electron occupies the lowestenergy orbital that can receive it
---- Beginning with the third energy
level, sublevels begin to overlap
Rules Governing Electron Configurations
---- The second rule is the Pauli exclusion principle, which says that no two
electrons in the same atom can have the same set of four quantum
numbers
---- The final rule is known as Hund’s rule, or the “empty bus seat” rule. This states
that orbitals of equal energy are each occupied by one electron before
any
orbital is occupied by a second electron, and all electrons in singly
occupied orbitals must have the same spin
Orbital and Electron Configuration
Examples of elements in both electron
and orbital notation.
Part 2:
Rules for Periods on the Periodic Table
by Melissa Thomas
Elements of the Second Period
---- The highest occupied energy level in the second period is n=2
---- The highest occupied energy level is the electron-containing main energy
level with the highest principal quantum number
---- Inner shell electrons are electrons at an energy level below the highest
occupied energy level
Noble Gas Notation
---- Group 18 elements are known as the noble gases
---- Each noble gas, with the exception of helium (He), has an electron octet in
its highest energy level
---- Noble-gas configuration is an outer main energy level fully occupied, in most
cases, by eight electrons
Elements of the Fourth Period
---- The 4s orbital if filled first, followed by 3d, and then 4p
---- The 3d sublevel is lower in energy than the 4p sublevel
Elements of the Fifth Period
---- The 5s sublevel is filled before the 4d sublevel, which is followed by 5p
---- The reason for this is the same reason as elements of the fourth period
Elements of the Sixth and Seventh Periods
---- The sixth period has 32 elements
---- Electrons are first added to the 6s orbital in Cesium and Barium, next the 4f,
then 5d, then 6p
---- The 13 elements after Cerium fill the 4f sublevels
---- The 4f and 5d sublevels are close in energy levels, so there are many
fluctuations in the order they are written for varying elements
---- The seventh period is incomplete with synthetic elements
In order to further understand
how the elements in each
period are written in
electron-configuration form,
you should study the chart in
the textbook on page 105.
Section Questions
Q: What are the three rules that determine how electrons are added to orbitals
and what do they state?
A: The Aufbau principle: an electron occupies the lowest-energy orbital that
can receive it. The Pauli exclusion principle: no two electrons can have the
same 4 quantum numbers. Hund’s Rule: that orbitals of equal energy are
each occupied by one electron before any orbital is occupied by a
second electron, and all electrons in singly occupied orbitals must have
the same spin.
Q: What happens to some of the sublevels after period 3?
A: Some of the sublevels begin to overlap, for example, 3d comes before 4s.
The End!