Chem Class- March 30, 2010

We can't believe we're already in Unit 6!

Solution Chemistry

- The study of chemical reactions in solutions

- A solution is a homogeneous mixture

- Solvents are components present in larger amounts

- Solutes are componets present in smaller amounts

- A solute is soluble in a solvent if it dissolves to form a homogenous mixture

- A saturated solution contains as much solute as possible

- An unsaturated solution can dissolve more solute

- Solubility is the measure of how much solute can dissolve in a given solution  (g/L, g/ml, mol/L, ppm)

- The solubility of Ba (NO3)2in water is 63 g/100 mL @ 25 degrees Celcius while the solubilty of Ba(NO3)2 in alcohol is is 1.6 g/ 100 mL @ 25 degrees Celcius

- Fators that can affect solubility: heat, changing the solvent and changing the solute

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Chem Class - March 26, 2010

We had an extremely short class today!
Here's some key points on electronegativity:

Electronegativity
- Atoms affinity for electrons
- Electronegativity increase from left to right and from bottom to top

- Polaritiy is the separation of charge inside something that is neutral

Chem Class - March 24, 2010

And so, we continue...

Covalent Bonding
- Electrons are shared between non-metals
- To draw Lewis Dot Diagrams:

1. Add the valence e- in all atoms
2. Identify which atom can form the most number of bonds. This will be the central atom
3. Bonds between two atoms are repesented by a line. This repesents 2e-.
4. Any e not creating bonds are placed in paris around the remaining atoms
5. All valence levels must be filled, all electrons must be used

Double and Triple Bonds
- Some compounds form more than one bond between two elements

(To the left of the element or compund is a Lewis Diagram and a Structural Diagram. You can see that there are sometimes two or three lines that separate the elements in the Structural Diagram. These represent the double and triple bonds.)

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For more help, this is a link that leads you to a geat little slide show on Lewis Dot Structures of Covalent bonds. It also gets you involved by having you type in the answers:
http://www.wisc-online.com/objects/ViewObject.aspx?ID=GCH6404

Chem Class - March 22, 2010

Back to Notes!

Atoms and Ions
- Atoms are electrically neutral
- # of protons = # of electrons
- Ions have a different number of protons and electrons
- Ions can either be positve (lose electrons) or negative (gain electrons)
- Cation = positive ion
- Anion = Negative ion

- Determine how many electrons each of the ions have and what type of ion they are:
Ca2+ = lost 2e-/cation
F- = gained 1 e-/anion
H+ = lost 1 e-/cation
Ag+ = lost 1e-/cation
H- = gained 1e-/anion
N3- = gained 3e-/ anion

- Determine how many protons, neutrons and electrons the following substances have:
76As3-/ p+ = 33/ n0= 43/ e- = 36
201Au+/ p+ = 79/ n0= 122/ e- = 78
56Fe3+/ p+ = 26/ n0= 30/ e- = 23

Bohr Diagrams for Ions
 - Draw the energy level or Bohr Diagram for the following ions:
Ca2+ 8e-/8e-/2e-
Li+ 2e-
F- 8e-/2e-
O2 8e-/2e-
P3- 8e-/8e-/2e-

Chemical Bonds
- A bond is an electrostatic attraction between particles
- Bonds occur as elements try to achieve Noble gas electron configuration
        - Noble gases (usually) do not form compounds or bonds
        - In Noble gases the outermost energy levels have stable octets

Lewis Dot Structures
- Atoms can be represented by dot diagrams
        - Dots represent electrons
        - Only valence electrons are shown
- Write the atomic symbol for the atom
             - This represents the nucleus and filled inner energy levels
- One dot is used to represent outer energy levles
         - One e- is placed in each orbital before any pairing occurs
         - Beginning with the 5th e-, pairing can occur up to a maximum of 8e-
- Below: Electron dot diagrams for different elements

Ionic Bonds
- Electrons are transferred from metal to non-metal
- No dots are shown on metal
- "Charged" species are written in brackets

- Example: Sodium Chloride




This video touches upon Ionic dot diagrams:

Chem Class - March 17, 2010

     THE CHEMICAL FAMILIES

     The vertical columns in the periodic table are known as groups or chemical families. There are five groups: Alkali Metals, Alkaline Earth Metals, Transition Metals, Halogens and Noble Gases. Hydrogen is actually in a separate group on its own. Elements in the same chemical family have similar physical and chemical properties.

     The Alkali Metals are in group 1 of the Periodic Table (points). IT includes Lithium, Sodium, Potassium, Rubidium, Cesium, and Francium. Elements in this family are highly reactive and reactivity increases as you go down the group. These metals have only one electron in their outer shell and so, they are always ready to lose that one electron in ionic bonding with other elements. They react readily with non-metals such as oxygen and water, and usually have lower densities than other metals. They also are malleable, ductile, good conductors of heat and electricity and have low melting points, all of which are below 200 °C. Finally, alkali metals are soft and can actually be cut with a knife.

     Elements in the second column are part of the Alkaline Earth Metal family. This includes Beryllium, Magnesium, Calcium, Strontium, Barium and Radium. They have two electrons in their outer shell and have low electronegativities. They are also less reactive than Alkali Metals but they will burn in air if heated. They will also react with water. They are all metals with a shiny, silvery white colour.

    

     The Transition Metals are the 38 elements in groups 3-12 of the periodic table. They are very hard, have high melting and boiling points, low ionization energies, high electrical conductivity and are malleable, which means that they are able to be shaped and bent.

     The Halogens are in group 17 of the periodic table. They are Fluorine, Chlorine, Bromine, Iodine, and Astatine. They are highly reactive non-metals with strong and unpleasant odours. In addition, they will burn flesh and do not react well with water. Fluorine and chlorine are gases at room temperature, Bromine is a liquid and Iodine and Astatine are solids.

     The last family is the Noble Gases, found in group 18 of the Periodic Table. They include Helium, Neon, Argon, Krypton, Xenon and Radon. The Noble Gases are the most stable and unreactive elements in the periodic table. They are colourless, odourless gases at room temperature. They also have high ionization energies and low boiling points.

Chem Class- March 15, 2010

We started presenting our projects today. Here's one group's perspective:

We made a poster board of Mendeleev teaching it to us on a blackboard, and our information would slide out from it. Elements are arranged by atomic number, not atomic mass because each element has different isotopes that all have different masses but have the same atomic number. We also gave our quiz orally to the class.

Mendeleev's Periodic Table
- 1867, a Russian chemist and teacher, Dmitir Meneleev started organizing every known element and is credited with creating the first real periodic table of elements

- He discovered a pattern and left holes in the table for elements that had yet to be discovered

- There are 118 elements in the Periodic Table as of March, 2010

- There are 7 periods and 18 columns

- Metals are on the left and non-metals are on the right

- Elements with similar properties fall into vertical columns

- Atomic Number: Number of protons of the nucleus of each atom of an element

- Atomic Mass: Mass of an average atom of an element (tends to increase along with atomic number)

- Ion charge: Electric charge that forms on an atom when it gains or loses electrons

Mendeleev's Periodic Table

Modern Periodic Table

Chem Class- March 9, 2010

We got a group project assigned today. We are to provide a summary on one of the following topics:

• Mendeleev's Periodic Table
• Metals
• Non-metals
• Metalloids
• Trends n Physical Properties of Elements on the Periodic Table
• Trends in chemical properties of elements on the periodic table (ion charge, chemical reactivity, ionization energy)
• Properties of Alkalis, Alkaline Earth Metals, Halogens, Noble Gases and Transition Metals

- The information is to be put on a poster. In addition, a handout and quiz is to be handed out to the class.

Chem Class- March 5, 2010

Emission Spectra
-Each element gives off a specific colour of light
- These are known as emission spectra
             - Unique to each element
             - Astronomers make use of this to find out which elements
               a star is composed of
- If electrons absorb energy they can be bumped to a higher level
- When they fall to a lower level they release that energy as light

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Atomic Structure
- Atoms are made up of parts called subatomic particles (protons, neutrons and electrons)

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Atomic Number

- Atomic Number = number of protons

 

A = atomic number/ B = Ion charge/ C = Symbol/

D = Element name/ E = Atomic Mass

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Isotopes
- The nymber of protons determine the type of element
- Changing the number of neutrons changes the isotopes of the element
- All isotopes have the same chemical properties

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Mass Number

- Mass number is the total of protons and neutrons

- Symbol given is A

- Different isotopes have different masses

- Mass number = atomic number + number of neutrons

A = Z + N

Let's say you're given the Isotope of 54-Fe. The mass would be 54, the atomic number would stay the same as it is given in the periodic table (26), the number of protons would be 26 (same as the atomic number) and the number of neutrons would be 28 (mass number - atomic number).

Try 14-C
Mass = 14/ Atomic number = 6/ Number of protons = 5/ Number of neutrons = 8


Here's a video on Isotopes as well as the Atomic Mass:

Chem Class- March 3, 2010

BOHR MODEL
- Atoms are electrically neutral
- Two different models can be used to describe the electron configuartion: Energy Level Model and Bohr Model- Electrons occupy orbitals: 2e in the first orbital, 8e in the second orbital (octet)and 8e in the third orbital (octet)


The video is very detailed. It explains the Bohr Model and it’s origin. So far we’ve only grazed the surface... So it’s fine to just ignore the formulas and specifics. The video does explain the Development of the Bohr Model, how electrons give off energy and briefly explains why Rutherford’s atomic model is defective.



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For the element Argon the Energy level model would look like this:
8e- 3rd level
8e- 2nd level
2e- 1st level

40
18 Ar   <-----the top number is the atomic mass and the bottom number is the atomic number or number of protons)

It's also good to note that the number of electrons is equal to the number of protons in a neutral atom, and the number of neutrons is equal to the atomic mass - the number of protons.

The Bohr model diagram for the element Argon would look like this:

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For the element Chlorine the Energy level model would look like this:

7e- 3rd level
8e- 2nd level
2e- 1st level

35
1 Cl

The Bohr model diagram for the element Chlorine would look like this:

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For the element Fluorine the Energy level model would look like this:

 7e- 2nd level
2e- 1st level

19
9 F


The Bohr model diagram for the element Chlorine would look like this:

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Orbital Shapes

- Atomic orbitals each have a specific name and shape

The atomic orbital on the left is 1s and the atomic orbital on the right is 2s. Notice that 2s is just bigger.

               Notice that the ps have the same shape that they are orientated differently (x is along the x axis, y is along the y-axis and z is along the z axis)
















Hybridized Orbitals
- The first of the Bohr levels is the 1st orbital and it holds 2e

- The second level contains 2s, 2px, 2py, 2pz orbitals. They combine (hybridize) to form one 2sp3 orbital.

Chem Class - March 1, 2010

Alright, so we're on to another chapter!

Atomic Theory

Early Atomic theory

Greeks:
In 300 BC, Democritus said atoms were invisible particles/
First mention of atoms/

Not a testable theory, only a conceptual model/

No mention of any atomic nucleus or its constituents/

Can't be used to explain chemical reactions/

This theory was the most accepted view for over 2000 years/

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Lavoisier (late 1700s)
Law of conservation of mass/

Law of definited proportions/

Wasn't a true atomic theory because it didn't discuss what atoms were or how they were arranged/
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Proust (1799)

If a compound is broken down into its constituents, the products exist in the same ratio as in the compound/

Experimentally provided Lavoisier laws/
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Dalton (Early 1800s)
Atoms are solid, indestructable spheres/

Provides for different elements/

Doesn't mention subatomic particles/

Can't explain isotopes/

No nucleus/

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J.J. Thomson (1850)

Raisin bub model/

Solid, positive spheres, with negative particles embedded in them/

First atomic theory to have positive and negative charges/

Introduces nucleus/

No mention of neutrons/

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Rutherford (1905)

Showed that atoms have a positive, dense center with electrons outside it/

Resulted in a planetary model/

Explains why eleectrons spin around nucleus/

Suggests atoms are mostly empty space/
Should be unstable/
No nucleus/
Doesn't explain valance level electrons/

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Bohr (1920s)

Electrons must only exist in specific orbitals around nucleus/

Explains how valance electrons are involved in bonding/
Explains difference between ionic and covalent bonding/
Resolves the problem of atomic instability/
Includes the neutron/
Explains atomic emisson spectra/