Notes: Chapter 11

 

·        Therefore, the more we understand about light, the more we can understand about the arrangement of electrons in the atom.

·        This last point is important because the electron is the most important subatomic particle in chemistry. The arrangement of an atom’s electrons, its electron configuration, is what determines an element’s chemical properties.

·        We will first discuss light as a wave phenomenon. Later, we will describe light in terms of being a particle.

·        Light is a transverse wave. A transverse wave is one in which the medium travels at right angles to the direction of the wave energy that is traveling through it.

·        A wave is simply some disturbance in a medium

·        A good example of a transverse wave is an ocean wave. The medium in this case would be the ocean.

c = ln

 

 

 

Electromagnetic Spectrum

The electromagnetic spectrum includes radio waves, microwaves, infrared light, visible light, ultraviolet light, x rays, and gamma rays. Visible light, which makes up only a tiny fraction of the electromagnetic spectrum, is the only electromagnetic radiation that humans can perceive with their eyes.

Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved.

 


 

 

The visible light spectrum. From left to right, in order of decreasing energy, decreasing frequency, and increasing wavelength.

 

 


 

 

E = hn

 

 

·        Practice problems:

o       Calculate the energy of a photon that has a frequency of 1.20 X 1015 Hz.

o       Calculate the frequency of a photon with an energy of 3.90 X 10-19 J.

·        Do problems 1-6, ch. 11, in class.

 

·        Do worksheet in class 

 

General Chemistry

Mr. MacGillivray

Worksheet:

Light and Quantum Theory

 

1.      Arrange the seven types of electromagnetic radiation that we discussed in class in order of DECREASING energy:

 

    1. _______ (highest E)
    2. _______
    3. _______
    4. _______
    5. _______
    6. _______
    7. _______ (lowest E)

 

  1. In the list above, use words and arrows to indicate how the wavelength and frequency are changing.

 

  1. Repeat #1 and #2 with the colors of the visible spectrum.

 

    1. _______ (highest E)
    2. _______
    3. _______
    4. _______
    5. _______
    6. _______
    7. _______ (lowest E)

 

  1. “If the wavelength of light is very short, then the energy is very __________ and the frequency is very _____________.”

 

  1. “If the wavelength of light is very long, then the energy is very __________ and the frequency is very _____________.”

 

  1. Wavelength and frequency are __________ly related. Energy and frequency are ___________ly related.

 

  1.  Energy is measured in these units: ________.
  2.  Wavelength is measured in these units: ________.
  3. Frequency is measured in these units: ________, also written as ______ or ______.
  4. Convert the following wavelengths to nm:
    1. l = 513 m

 

    1. l = 8.03 x 10-6 m

 

  1.  Convert the following wavelengths to m:
    1. l = 755 nm

 

    1. l = 0.272 nm

 

  1.  Find the energy of a photon of light with a frequency of 5.22 x 1021 1/s.

 

 

 

  1. Find the energy of a photon of light with a wavelength of 425 nm.

 

 

 

  1. Find the wavelength of light with a frequency of 5.28 x 1015 s-1.

 

 

 

  1.  Using p. 299, answer these questions:
    1. Is the light in question #12 visible?
    2. How did you know?
    3. Is it too high in energy or too low in energy to be seen?
    4. What type of light is it (what region of the electromagnetic spectrum)?

 

 

 

 

 

 

·        Begin electron configurations

·        Chemistry: it’s the study of matter and the changes it undergoes

·        These changes are due to atoms combining, separating, or rearranging.

·        These changes occur when electrons are given, taken, or shared between atoms

·        The more we know about the electronic structure of the atoms,

·        There are 3 levels of organization to the electron cloud.

o       Energy level (“n”)

o       Energy sublevel (“l”)

o       Orbital (“ml”). An orbital is a region in space where electrons are likely to be found. It can contain at most two electrons.

·        Think of the atom as a hotel with different floors (energy levels), rooms on each floor (energy sublevels), and closet/bathroom/bedroom/etc. (orbital) within each hotel room.

·        Each energy level has a different number of sublevels

o       The first energy level has 1 sublevel, “1s”

o       The second has energy level has 2 sublevels, 2s and 2p

o       The third energy level has three energy levels, 3s, 3p, and 3d

o       The fourth energy level has four energy levels, 4s, 4p, 4d, and 4f

o       The fifth has five, and so on.

o       How many sublevels does the 7th energy level have?

·        Sublevels are in turn divided up into orbitals, which are regions in space where electrons are likely to be found. It can contain at most two electrons.

o       Any s sublevel has 1 orbital

§         1s has one orbital

§         2s has one orbital

§         3s has one orbital

§         10s has one orbital, etc.

§         An s sublevel is spherical in shape

§         Any s sublevel has one orbital, which can hold 2 electrons at most. Therefore, any s sublevel can hold at most 2 electrons.

o       Any p sublevel has 3 orbitals.

§         2p, 3p, 4p, etc. all have three orbitals each.

§         p orbitals look like dumbbells, and are right angles to one another in 3-dimensional space. They can be thought of as being oriented on three axes (x, y, and z).

§         They are called the px, py, and pz orbitals.

§         Because any orbital can contain at most 2 electrons, and because any p sublevel has three orbitals, any p sublevel can contain at most 6 electrons.

o       Any d sublevel has 5 orbitals.

§         The 3d sublevel has 5 orbitals. So does the 4d and so on.

§         That means that any d sublevel can hold a maximum of 10 electrons.

§         The shapes and orientations of the d orbitals are complex.

o       Any f sublevel has 7 orbitals.

§         The 4d sublevel has 7 orbitals. So does the 5d and so on.

§         That means that any f sublevel can hold a maximum of 14 electrons.

§         The shapes and orientations of the f orbitals are complex.

 

Sublevel type

# of orbitals

Max # of electrons in sublevel

s

1

2

p

3

6

d

5

10

f

7

14

g, but not important to us

9, but not important to us

18, for the sake of demonstration

Who cares

11, but who cares

22, but don’t lose sleep

 

 

Energy level (=n)

Sublevels present

# of orbitals (=n2)

Max # of electrons (=2n2)

1

1 (1s)

1

2

2

2 (2s, 2p)

1+3 = 4

2 + 6 = 8

3

3 (3s, 3p, 3d)

1+3+5 = 9

2 + 6 + 10 = 18

4

4 (4s, 4p, 4d, 4f)

1+3+5+7 = 16

2 + 6 + 10 + 14 = 32

5

5 (5s, 5p, 5d, 5f, 5g)

1+3+5+7+9= 25

2 + 6 + 10 + 14 + 18 = 50

6

6, etc.

1+3+5+7+9+11= 36

2 + 6 + 10 + 14 + 18 +22= 72

7

7, etc.

1+3+5+7+9+11+13= 49

2 + 6 + 10 + 14 + 18 +22 + 26 = 98

 

 


 

 

 



 

 


 




 

 


 

o       What does the word “periodic” mean? “periodical”? “periodicity”?

 

Dmitiri Mendeleev, 1834-1907

 

o       The first periodic table was devised by a Russian chemist, Dmitri Mendeleev. Mendeleev arranged his periodic table by increasing atomic mass.

o       Groups, a.k.a. families – these are the vertical columns of elements. Elements in the same families have similar chemical and physical properties.

o       Periods – these are the horizontal rows of the periodic table. Elements in the same period have very different properties, for the most part.

o       Good conductors of heat & electricity

o       Malleable

o       Ductile

o       Lustrous

o       Poor conductors (insulators)

o       Brittle

o       Dull

o       Properties that are somewhere in between those of metals and nonmetals

o       Example: silicon (Si). It is shiny but brittle. It is a semiconductor, which is a material that is neither a good conductor nor good insulator. It can control the flow of electrons (electricity).

·         Numbering system of the groups: we will use the easy, new system: 1 through 18.

·         Group names that you should know:

o        Alkali metals (group1)

o        Alkaline earth metals (group 2)

o        Chalcogens (group 16)

o        Halogens (group 17)

o        Noble gases, a.k.a. inert gases (group 18)

o        Transition metals (d-block elements)

o        Inner transition metals (f-block elements)

o       Noble gases

§         Unreactive elements, always found alone  in nature

o       Gold, Silver, Platinum

§         Relatively unreactive metals, often found chemically pure  (or nearly so) in nature

o       Most other elements are found combined with other elements as compounds.

o       Some elements combine with themselves to form diatomic molecules:


§         H2

§         N2

§         O2

§         F2

§         Cl2

§         Br2

§         I2


 


 

Periodic Trends 

o       Atomic radius is the distance from the center of the atom to the outer edge of the atom

o       It is a way of measuring the size (in distance) of atoms

o       The periodic and group trends are

§         L to R, the atoms decrease in size

§         T to B, the atoms increase in size

o       Reasons for the trend:

§         As you go down a group, the number of “shells” or energy levels of electrons between the positive nucleus and the negative nucleus increases.

§         This decreases the attraction between the nucleus and the outermost electrons.

§         The effect is that the electrons are less tightly held, and therefore are able to get further away. This is called the shielding effect.

§         As the atomic number across a period increases (L to R), the number of electrons (in the outermost energy level) and the number of protons (in the nucleus) both increase.

§         Without the shielding effect of adding more “layers” of electrons between the nucleus and these additional electrons, the net effect is to draw the outermost electrons closer to the nucleus.

§         “more protons + more electrons = stronger attraction”: . . . within a given period.


o       Ionization energy is the energy required to remove an electron from an atom

o       Metals give up electrons more easily than nonmetals; metals will attain a full octet by losing relatively few electrons.

o       Nonmetals will attain a full octet more easily by gaining electrons than by losing them.

o       Thus, the trends are

§         L to R ionization energy increases

§         T to B ionization energy decreases


o       Electronegativity is the tendency of an atom to attract electrons toward itself when bonded to another atom

o       Metals have low electronegativities

o       Nonmetals have high electronegativities

o       Thus, the trends are

§         L to R electronegativity increases

§         T to B electronegativity decreases