Title: Models of the Atom Section 13.1
1Models of the AtomSection 13.1
- The story of how the atomic theory has evolved
over time.
2John Dalton
- The atom is a solid indivisible mass.
- He had several key ideas
- All elements are composed of tiny indivisible
particles called the atom. - Atoms of the same element are identical.
- Atoms of different elements are different.
- Atoms combine chemically with one another in
simple whole-number ratios. - During chemical reactions, atoms are separated,
joined, or rearranged. Atoms are never created
nor destroyed.
3JJ Thomson
- Plum-pudding model.
- I call it the Chocolate Chip Cookie Model
- The atoms has negatively charged electrons stuck
into a lump of positively charged material, like
chocolate chips stuck in a cookie dough. - Did not address protons and neutrons.
4Ernest Rutherford
- Discovered the nucleus.
- Showed that most of an atoms mass is
concentrated in a small, positively charged
region called the nucleus. - Electrons resided on the outside.
- Did not address how electrons were arranged.
5Neils Bohr
- Electrons are arranged on concentric circular
paths, or orbits around the nucleus. - Solar system model or planetary model.
- Gave us the idea of definite energy levels.
6Quantum Mechanical Model Our Currently Accepted
Model
- Erwin Schrodinger
- Primarily a mathematical model using quantum
mechanics - It addresses probabilities of finding an
electron at any instant in an area called
electron clouds. - Introduced the ideas of Principal Energy Levels
and Sublevels of energies. - The electron clouds take certain shapes,
represented by the s,p,d,f subatomic orbitals.
7Principal Energy Levels
- Just like the Bohr model, the Quantum Mechanical
Model designates energy levels of electrons by
means of principal quantum numbers - Principal Energy Levels refers to a major region
where electrons are most likely to be found. - They are assigned values in order of increasing
energy 1, 2, 3, etc.
8Sublevels
- Within each principal energy level, the electrons
occupy energy sublevels. - The number of sublevels within each principal
energy level is the same as the principal quantum
number. - How many sublevels does the 4th principal energy
level have?
9Atomic Orbitals
- The regions in which electrons are likely to be
found are called atomic orbitals. - Letters denote the atomic orbitals
- S-shape orbitals are spherical
- P-shape orbitals are hour-glass shapes
- D-shape orbitals have clover-leaf shapes
- Draw an example of each into your notes.
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11Exploring further
- The lowest principal energy level has only one
sublevel, called 1s. - The second principal energy level has 2
sublevels, the 2s and 2p. The 2p is higher in
energy and consists of three p orbitals.
12The Electron Pyramid
- The s orbitals have 1 spatial orientation,
therefore can hold 2 electrons - The p orbitals have 3 spatial orientations,
therefore can hold 6 electrons - The d orbitals have 5 spatial orientations,
therefore can hold 10 electrons - The f orbitals have 7 spatial orientations,
therefore can hold 14 electrons.
13Electrons Fill following 3 simple rules
- Aufbau principle Electrons enter the lowest
energy level first. - Pauli Exclusion Principle An atomic orbital may
describe at most 2 electrons, both spinning in
opposite directions. - Hunds Rule When electrons occupy orbitals of
equal energy, one electron enters each orbital
until all the orbitals contain one electron with
parallel spins.
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16Exceptional Electron Configurations
- Chromium and Copper have exceptional electron
configurations. - They fill their d sublevel completely, leaving
their 4s partially filled. - Much more stable this way!
- Write them correctly into your notepacks
17Physics and the Quantum Mechanical Model
- This section studies the electron as a property
of light. - Electrons travel as waves and are made of
particles of light called photons - According to the wave model, light consists of
ELECTROMAGNETIC RADIATION.
18Electromagnetic Spectrum
- This form of energy includes
- Gamma rays
- X-rays
- Ultraviolet rays
- Visible light
- Infrared rays
- Radar
- FM
- TV
- Shortwave
- AM
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20Electromagnetic Spectrum
- Every element emits light when it is excited by
the passage of electric discharge through its gas
or vapor. - The atoms first absorb energy, then lose the
energy as they emit light.
21Electromagnetic Spectrum
- Electrons are said to move from their GROUND
STATE (lowest energy level) to and EXCITED STATE
(higher energy level). - When the electron falls back to its lower energy,
it emits a PHOTON of energy, and can be seen in
the visible spectrum.
22Electromagnetic Spectrum
- Passing the light emitted by an element through a
prism gives the ATOMIC EMISSION SPECTRUM of the
element. - Because each atom has a unique electron
arrangement, each atom emits a unique wavelength
during this process. This wavelength falls
within the visible spectrum.
23Kernel Structures
- The kernel is a structure used to shorten an
electron configuration. - A kernel is an inert gas symbol in brackets that
stands in place of all of the filled orbitals
contained in the inert gas. - Examples
24Honors The Quantum Concept and the
Photoelectric Effect
- Electrons travel as waves around the nucleus of
an atom. Lets review the concept of wave
mechanics
25Definitions
- Amplitude the height of a wave from its origin.
- Wavelength the distance between the crests l
- Frequency the number of wave cycles to pass a
given point per unit of time. n - Hertz a per second unit for n.
26Speed of light, c
- The frequency and wavelength are inversely
related as shown by this relationship - c ln
- The speed of light is a constant
- C 3.0 E 8 meters/second
- Examples
27Honors Photoelectric Effect
- By studying black body radiation, German
physicist Max Planck described mathematically
that the amount of radiant energy (E) absorbed or
emitted by a body is proportional to the
frequency of the radiation. - E h x n
- h Plancks constant, 6.63 E -34 J-s
28Albert Einstein
- Nobel Prize Winner!!
- In 1905, Albert Einstein proposed that light
could be described as quanta of energy that
behave as if they were particles he called
PHOTONS. - In the PHOTOELECTRIC EFFECT, metals eject
electrons when light shines on them. - Photoelectric cells
- Automatic doors at Meijer!
29(Honors) Quantum Mechanics and Matter Waves
- In 1924, Louis De Broglie derived an equation
that described the wavelength of a moving
particle, such an electron. - l h/mv
- M mass (in kg)
- Mass x velocity momentum
- h is Plancks constant
30Matter Waves
- If the mass of an electron is 9.11 E -28 grams
and moving nearly at the speed of light, an
electron has a wavelength of about 2 E -10 cm.
31 - De Broglies prediction that matter would exhibit
both wave and particle properties is summarized
in the following two statements - 1. Classical mechanics adequately describes the
motions of bodies much larger than the atoms that
they comprise. - 2. Quantum mechanics describes the motions of
subatomic particles and atoms as waves. These
particles gain or lose energy in packages called
quanta.
32Honors Quantum Numbers
- 4 Quantum numbers are used to describe a single
electrons position within an atom. - 1. Principal quantum number (n) size and energy
of an orbital. - Has integer values gt0
33Quantum numbers
- 2. Angular momentum quantum number l
- shape of the orbital.
- integer values from 0 to n-1
- l 0 is called s
- l 1 is called p
- l 2 is called d
- l 3 is called f
- l 4 is called g
34Values of l 0 1 2 3
Letter used s Sharp p Princi-pal d Diffuse f Funda-mental
35Quantum numbers
- 3. Magnetic quantum number (m l)
- integer values between - l and l, including
zero. - Describes the orientation of the orbital in
space. - 4. Electron spin quantum number (m s)
- Can have 2 values.
- either 1/2 or -1/2
3614.1 Classification of the Elements
- By Electron Configuration
37Classifying Elements by Electron Configuration
- Of the three major subatomic particles, the
ELECTRON plays the most significant role in
determining the properties of an element. - The arrangement of elements in the PERIODIC TABLE
depends on these properties.
38Elements can be classified into 4 categories
- The Noble Gases
- These are elements in which the outermost s and
p sublevels are filled. - Write for Helium, Neon, Argon, Krypton
39Elements can be classified into 4 categories
- The representative elements
- In these elements, the outermost s and p
sublevel is only partially filled. - Write for Lithium, Sodium, Potassium, Carbon,
Silicon, Germanium
40Elements can be classified into 4 categories
- The transition metals
- These are metallic elements in which the
outermost s sublevel and nearby d sublevel
contain electrons. - Write for Zinc and Zirconium.
41Elements can be classified into 4 categories
- The inner transition metals
- These are metallic elements in which the
outermost s sublevel and nearby f sublevel
generally contain electrons.
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4314.2 Periodic Trends
- Atomic radius ½ the distance between the nuclei
of two like atoms in a diatomic molecule.
44Group Trends
- Atomic size generally increases as you go down a
group on the periodic table. - Adding additional energy levels!
45Periodic Trends
- Atomic size generally decrease as you move from
left to right across a period. - Same energy level -
- increasing nuclear charge pulls electrons closer
to nucleus.
46Ionization Energy
- An ion a charged atom that results from either
losing or gaining an electron. - Ionization Energy The energy required to
overcome the attraction of the nuclear charge and
remove an electron from a gaseous atom. - (The ease of losing an electron and forming a 1
charge)
47Ionization Energy
- First ionization energy the energy needed to
remove the first electron from an atom. - Second ionization energy the energy needed to
remove the second electron from an atom, etc.
48Ionization Energy
- Group Trends The first ionization energy
generally decreases as you move down a group on
the periodic table. - The size of the atoms increases, so the outermost
electron is farther from the nucleus and will be
more easily removed.
49Ionization Energy
- Periodic Trends For the representative
elements, the first ionizatoin energy generally
increases as you move from left to right across a
period. - Increasing nuclear charge makes it more difficult
to remove an electron.
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51Ionic Size
- The atoms of METALLIC elements have low
ionization energies. They form POSITIVE ions
easily. - By contrast, the atoms of NONMETALLIC elements
readily form NEGATIVE ions.
52Trends in Ionic Size
- Positive ions are always smaller than the neutral
atoms from which they form. - They lose their outer shell electrons
- Negative ions are always larger than the neutral
atoms from which they form. - This is because the effective nuclear attraction
is less for an increased number of electrons.
53Trends in Electronegativity
- Electronegativity the tendency for the atoms of
the element to attract electrons when they are
chemically combined with atoms of another
element. - Electronegativity generally DECREASES as you go
down a group. - As you go across a period from left to right, the
electronegativity of the representative elements
INCREASES.
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55Electronegativity
- The electronegativity of cesium, the least
electronegative element is 0.7 - The electronegativity of fluorine, the most
electronegative element, is 4.0 - Electronegativity values help predict the type of
bonding that can exist between atoms in
compounds, either IONIC OR COVALENT bonds.
56Summary of Periodic Trends
- Using page 406, create a summary of periodic
trends into your notes.