Sunday, May 27, 2012

Alkanes, Alkenes, Alkynes & Halides, Nitro, Alcohol, Ketones, Aldehydes--By Nemo Jin

Alkane
--all carbon atoms bonded by single bond
--general form "CaH2a"
--alkyl groups: alkane lost one hydrogen



Alkene & Alkyne
--"ene" double bonded carbon atoms
--"yne" triple bonded carbon atoms
--same naming rules, give double/triple bond the lowest number
--larger groups are diagonal: trans
--larger groups are at either bottom or top: cis

Ex.
















 Ex.

















Functional Groups
--most reactive part of the molecule
--insoluble in water
--F is less reactive; Cl, Br are the most reactive ones
--NO2: tend to be explosive

           F = fluoro
            I = iodo
          Cl = chloro
          Br = bromo
      NO2 = nitro


Ex.





Alcohol
--using the largest chain containing the OH group
--replacing the "e" ending in parent hydrocarbon chain with "ol"
--give OH the lowest number

general form:


Ketone &Aldehyde
--Aldehyde:
   -double bonded oxygen at the end of main chain
   -change the ending to "al"
--Ketone:
   -double bonded oxygen that's not on either end
   -change the ending to "one"

for more info:
http://www.brooklyn.cuny.edu/bc/ahp/LAD/C4c/C4c_aldehydes.html








Thursday, May 24, 2012

Ester, Ether, Carboxylic Acids and Amines - By Sally Chen

Ester
- formed by 
- alcohol + carboxylic acid = ester
- fruity smell
- main chain:  drop "e" add "oate"
- counting starts on the double bonded oxygen end

Ether
- formed by 
- highly flammable
- insoluble in water
- good solvent for organic compounds
- side chain:  drop "e" add "oxy"
- counting starts on the oxygen end


Carboxylic acids
- formed by 
- can be neutralized by a base
- main chain:  drop "e" add "oic acid"
- counting starts on the double bonded oxygen end


Amines
- formed by 
- base
- primary amine = 1 carbon chain
  secondary amine = 2 carbon chain
  tertiary amine = 3 carbon chain
- closely related to NH3
- soluble
- fishy smell
- add "amino" between parent chain and side chain(s)
- counting:  whichever way makes the numbers smaller

I don't know how it just doesn't work out with the "Insert a Video" button, so here:
http://www.youtube.com/watch?v=mAjrnZ-znkY

Tuesday, May 15, 2012

Electronegativity, Polarity and VSEPR--By Tina Zhao

Electronegativity
- The attraction an atom has for the shared pair of electrons in a chemical bond
- It is the difference in electronegativity between two atoms that determines the degree of electron sharing which occurs between the two atoms
- Electonegativity refers to how much atoms want to gain electrons
- The top right corner of the periodic table has the highest electronegativity.Fluorine is the MOSTelectronegativity element, and the lowest electronegativity value is Francium with a value of 0.7
- If an atom has high Electronegativity value indicates that it readily pull on electrons in  a bond
-If an atom has low Electronegativity value indicates that it doesn't readily pull on electrons within a bond
- Electronectivity increase as you go across a row from left to right, and decrease as you go down a group
- The scale that is most commonly used to messure electronegativity is called the Pauling scalt , this scale range from 0.7 to 4.0
-High electronegativity values have high ionization energy because they strongly attract their valence electron and they are difficult to remove
- If the electronegativity difference < 0.5 it is a COVALENT bond
- If the electonegativity difference greater and equal the 0.5 or less and equal than 1.8 it is A POLAR COVALENT bond


Polarity
- Describes a molecule's electrical balance
- If there is an imbalance with electrical charge, then a molecule is polar
- If the electrical charge is the same strength on all sides of the molecule, then it is nonpolat


Polar Covalent Bonding
- electonegativity difference between 0.3 and 1.6 are considered to be covalent but with unequal sharing of elecreons , because the bond has slightly positive and slightly negative poles that form at each end
- Higher electronegativity will form a PARIAL NEGATIVE charge, and lower electronegativity will form a PARTIAL POSITIVE charge 
- An arrow sigh is usually used to indicate the migration of electons towards the more electronegativity

EX:
For CH3C1, C has a value of 2.5; H has a value of 2.1 and Cl has a value of 3.0.

...................H (2.1)
....................|
H(2.1) --------- C(2.5) ----------- Cl (3.0)
....................|
...................H (2.1)

Between the Hydrogen's and carbon there is a difference of 0.4, and between the carbon and chlorine there is a difference of 0.5.
VSEPR (The Valence Shell Electron Pair Repulsion

- For polyatomic molecules containing 3 or more atoms, one of the atoms is called the central atom to which other atoms are linked.
- The geometry of a molecule depends upon the total number of valence shell electron pairs (bonded or not bonded) present around the central atom and their repulsion due to relative sizes and shapes.
- If the central atom is surrounded by bond pairs only. It gives the symmetrical shape to the molecule.
- If the central atom is surrounded by lone pairs (lp) as well as bond pairs (bp) of then the molecule has a distorted geometry.
- The relative order of repulsion between electron pairs is as follows: lp – lp > lp – bp > bp – bp.
A lone pair is concentrated around the central atom while a bond pair is pulled out between two bonded atoms. As such repulsion becomes greater when a lone pair is involved.

  • linear molecule :with a 180o angle 
  • trigonal planar :with angle of 120



  • - If the electronegativity difference >1.8 it is an IONIC bond

    Sunday, May 13, 2012

    Chemical Bonding & Electronic Dot Structure -- by Ria Park

    Chemical Bonds

    Chemical Bonds 
    • are formed when the electrons of one atom are attracted by the nucleus if another atom.
    • are formed with various degrees of sharing of electrons between two atoms
    • COVALENT BOND is formed when the electrons are shared equally between two atoms
    • When the electrons of one atom are given away completely to another atom, both a positively charged ion and a negatively charged ion are formed
    • The force holding the two ions together is called an IONIC BONDS
    Covalent Bond
    Ionic Bond















    Lewis Structure
    • represents valance electrons.
    • uses dots to represent electrons, focuses on an atom's valence electrons only.
    • The electrons that are in pairs are Lone pairs or Nonbonding electrons.
    • These are not used to bond since the orbital they are in already has its full complement if electrons.
    • The unpaired electrons are Bonding electrons. They are capable of making one single covalent bond.
    • An atom needs to have 2 bonding electrons when we make a double covalent bond.
    • To make a triple covalent bond, an atom needs 3 bonding electrons.

    Now single covalent bond is forme
    Double Bond
    Triple Bond


    Example of Lewis Structure








    Saturday, April 21, 2012

    History of the Atom - By Sally Chen

    Aristotle
    - Democritus:  suggested that the differences between substances were the direct result of differences in the size and shape of tiny, uniform, unbreakable particles.

    - Aristotle:  4 basic elements:  water, air, fire and earth.
    Antoine Lavoisier:  created the first law of the conservation of mass.
    - John Dalton:  created Dalton’s Atomic Theory, which is a combination of all discoveries about atoms.
    J. J. Thomson:  He discovered the existence of electron in 1897.  He found it was about 2000 times less than the mass of hydrogen.
    Ernest Rutherford:  He discovered the atomic nucleus and presumed the nuclear structure of the atom and predicted the existence of the neutron.
    Robert Millikan:  He accurately determined the charge carried by an electron, using “falling-drop method”.  He also demonstrated that this quantity was a constant for all electrons.
    Marie Curie:  She and her husband Pierre Curie isolated the elements polonium and radium.  She also developed methods for the separation of radium from radioactive residues.
    Albert Einstein
    - James Chadwick:  He discovered the neutron, and that it had about the same mass as a hydrogen atom.
    Max Planck:  He discovered that light was released by heat sources in a particular pattern of frequencies for different elements.  Each frequency of light corresponded to different sets of colors of lights seen by our eyes (lowest to highest:  red, orange, yellow, green, blue, purple, and violet).
    Albert Einstein:  In 1905 Einstein projected a theory that light was made up of localized particles.  He also defined detailed equations on light wavelengths and frequency differences within the same light.  He named packets of light energy photons.  Einstein believed that each atom oscillates independently instead of joining to others.
    Joseph Louis Proust
    Niels Bohr:  electric fields between negatively charged electrons and a positively charged nucleus must hold electrons in their orbits.  He thought that electrons could circle at different orbit levels above the nucleus depending on how much energy they had.  When electrons jumped to lower levels, Bohr suggested that energy would be released as light.  The diagram of his version of atom is called the Bohr Diagram.
    Louis De Broglie:  He discovered the wave nature of electrons.  He had a theory that the behavior of the electron could also be better understood not just as a particle, but as both a particle and a wave.
    Erwin Schrodinger:  He created an equation describing how Broglie’s theory would be possible, not only for atoms and parts of the atom, but even for large objects – maybe even for the entire universe.
    - Joseph Louis Proust:  He discovered the law of definite proportions, also known as Proust’s law, which states that chemical compounds always have the same fraction of each element in them by mass.
    - Henri Becquerel:  He was the first person who discovered radiation.

    History of Periodic Table--Nemo Jin


    Long time ago, a group of people believed that they could turn metals into pure gold. These people were called alchemists. Although they were not successful, many different elements were discovered by these alchemists, including gold, silver, tin, copper, lead and mercury. However, the first scientific discovery of an element was in 1649, the discovery of phosphorous by Hennig Brand.
    In the next 200 years, a total of 63 elements had been discovered, and scientists began to recognize patterns in properties and began to develop classification schemes.


    In 1863, John Newlands, a English chemist divided 56 elements into 11 groups, based on their characteristics. He also proposed the Law of Octaves,which stated that any given element will exhibit analogous behavior to the eighth element following it in the table.




                                                 (John Newlands' Periodic Table)


    (Meyer's 1864 textbook included a rather abbreviated version of a periodic table used to classify the elements, but unfortunately for Meyer, Mendeleev's table was the first one available to the scientific community)


          “Father of Periodic Table"
    In 1869, Russian chemist Dimitri Mendeleev arranged chemical elements by their atomic masses.  He also accurately predicted the properties of some undiscovered elements, leaving spaces open in his periodic table for them. His contribution to the development of periodic table was usually considered as the foundation of modern periodic table. 





    In 1894, Sir William Ramsay and Lord Rayleigh discovered the noble gases which did not fit any of the known periodic groups. Because of the zero valency of the elements, noble gases were added to the periodic table as group 0


    In 1911, A. van den Broek proposed that the atomic weight of an element was approximately equal to the charge on an atom. This charge, later termed the atomic number, could be used to number the elements within the periodic table.

    The last major changes to the periodic table was in the middle of the 20th Century.


    Glenn Seaborg 
    --discovery of elements from 94 to 102 
    --rearrangement of the periodic table (placing the actinide series below the lanthanide series) 
    He was awarded the Nobel Prize in chemistry for his work. Element 106 has been named seaborgium (Sg) in his honor.


















    Friday, April 20, 2012

    Electronic Structure of the Atom--By Tina Zhao

    Electronic Structure of the Atom
    - The electronic configuration of an atom is notation that describes the orbitals in which the electrons occupy and the total number of electrons in each orbital
    -Helps to understand the structure of the periodic table of elements

    Energy Level
    - is the amount of energy, which an electron in an atom can possess "n" is the number of the energy level
    - the energy difference two particular energy levels are called the quantum of energy


    Ground State: When all the electrons of an atom are in their lowest possible energy level
    Excited State: When one or more of an atoms's electrons are in energy
    An orbital is the actually region of space occupied by an electron in a particular energy level
    A shell is the set off all orbital having the same n-value
    A sub-shell is a set orbital in same level

    For a given value of "n", different types of orbitals are possible:
    n=1; only the s-type
    n=2; s and p- types
    n=3; s,p,and d-types
    n=4; s,p,d,and f-types

    * A maximum of 2 electrons place in one orbital

    Writing Electronic configurations for Neutral Atoms
    - Always start with lowest energy level first 
    - Figure out how many electron you have (neutral number= atomic number) then start  at the lowest energy level (1s)
    - Each electrons has an opposite spin

    * the 2 electron in the 2p occupy separate suborbitals and are not paired up 

    Writing Electronic configurations for ion
    Negative ion: Add electrons (equal to the charge) to the last unfilled sub-shell, starting where the neutral atom left off
    Positive ion: Start with the neutral configuration, and then remove electrons from the outmost shell first

    Core Nation
    - The set of electrons for an atom can be divided into two subsets; the core electrons and the outer eletrons
    - The core of an atom is the set of electrons with the configuration of the noble gas
    - The outer electrons consist of all elections outside of core. Core electrons  normally take part in chemical reaction
    - Locate the atom and not the noble gas at the end of the row above the element

    Predicting the number of Valence Electrons
    - are electrons which can take part in chemical reactions 
    - or are all the electrons in an atom EXCEPT those in CORE AND IN FILLED d OR f -sub-shells