Alkenes and Alkynes (Double & Triple bonds)

Alkenes and Alkynes (Double & Triple bonds)

-Each carbon can have 4 bonds:

 Carbon can form double & triple bonds with carbon atoms, when multiple bonds form, fewer hydrogen will attach the carbon atom

-The position of the double/triple bonds always has the lowest number and is put in front of the parent chain. Ex.

2-pentene

1-pentene 

-Naming rules are almost same as Alkanes, just change –ane to –ene foe Alkenes

For example CH2=CH2 ehene CH2=CH–CH3 1-propene or propene

-as we know, the general formula for Alkanes is C_nH_{2n+2 ,} here have another formula for Alkenes  is C_nH_2n

Naming rules:

1) Find the longest chain and place it at the end of the name

2) Number the carbon atoms to get the lowest number for the start of the double bond and place that number before the parent name.

3) Assign names and numbers for all side groups and assemble the name alphabetically (videos)http://www.youtube.com/watch?v=KWv5PaoHwPA

Alkenes: some molecules will have the same structure, but have different geometry.-these called geometric isomers

-          trans & cis butane  eample:

.

1. If the larger groups are both above H or below R the plane of the bond, the double bond is termed a “cis” double bond

2. If the larger groups are across the plane of the bond (H or R), the double bond is termed a “trans” double bond

3. If there are two identical groups on either end of the double bond (H or R), there are no geometric isomers, and no need for cis or trans in the name

Alkynes (hydrocarbons)- triple bonds between carbon atom  (-yne for alkynes)

-Naming rules: (general formula: C_nH_2n-2)

The naming rules are “mostly” the same as the alkenes (with no cis or trans!)

1) Find the longest chain (and write at the end)

2) Number the carbon atoms to get the lowest number for the start of the triple bond and write that number before the parent name

3) Assign names and numbers for all side groups and assemble the name alphabetically

Double bonds (Alkenes) end in –ene Triple bonds (Alkynes) end in -yne

http://www.youtube.com/watch?v=CJYzbs_vyUs

Bohr Models and Diagrams

Bohr (1920)

1. Protons and electrons attract each other, so that Rutherford’s models are unstable. When matter is heated, it will emit light.
2. .Light travels as photons (wavelength)
3.  Each atom has different spectra of light

Bohr based his model on the emission of light. To explain this, he presumed some theory:

1. Electron exist in orbital or shells
2.  Because matter is unstable. When they absorb energy, they move to a higher orbital. When they release energy, they move to a lower orbital.

Protons=11    Atomic Mass= 23.0  

Neutrons=23-11=12      (one valence electron) - so sodium always form an ion with 1+ charge

- Two different models can be used to describe electron configuration:

1. Energy Level Model

2. Bohr Model

-Here are some rules about how electrons occupy shells:

1. 2 e- in the first orbital
2.  8 e- in the second orbital
3.  8 e- in the third orbital

-the electrons were absorbing and then emitting energy from different energy levels around the atoms and proposed his model of the atom

http://www.youtube.com/watch?v=-YYBCNQnYNM&feature=related

Organic Chemistry--Functional Groups

Functional Groups are organic compounds can contain elements other than C and H.

Ex. Alcohols, Halides and Nitro, Aldehydes, Ketones

Halides and Nitro Compounds

- they can be attached  to alkanes, alkenes, and alkynes

- add the following prefixes in front of the main chain:

F: fluoro

Cl: chloro

Br: bromo

I: iodo

NO2: nitro

Ex. 1, 2, 3-trichloropentane

Alcohols

- contains an -OH functional group

- when naming an alcohol, use the longest chain that contains the OH group

- the "e" ending in the parent hydrocarbon is replaced by "ol"

Ex. 3-ethyl-2-pentanol

- If there are more than one -OH group, add -diol, -triol, etc. endings

Ex. 1,2-butanediol

Aldehydes:

- a compound that contains a double bond oxygen at the end of a chain

- change the parent ending to "-al"

Ex. propanal

Ketones:

- a compound that contains a double bond oxygen that is not on either end

- add "-one" ending to the parent hydrocarbon

Ex. 4-methyl-3-heptanone

May 26--Organic Chemistry

Organic Chemistry -- The chemistry of CARBON compounds.

Some of the examples in our everyday life:

clotting--polyester

plastic--polyethyiene

Organic Compounds properties:

1.  low melting points

2.  weak or non-electrolytes

3.  can form chains of CARBON atoms that are linked in a

         STRAIGHT LINE, CIRCULAR PATTERN and BRANCHED PATTERN.

Three types bonds:single bond, double bond, and triple bond.

Alkanes(unbranched)

1. Hydrocarbon compounds

2. Non-polar molecules

3. Tetrahedron Geometry

Naming Alkanes :ends with "-ane"

Examples:

Ethane

 Names of Alkanes(needs to memorize!)



Methane   CH4	Hexane     C6H14
Ethane    C2H6	Heptane    C7H16
Propane   C3H8	Octane     C8H18
Butane    C4H10	Nonane    C9H20
Pentane   C5H12	Decane    C10H22

* An easy formula to memorize the above  CNH2N+2

Branched Hydrocarbon

Hydrocarbons can have branched which are also hydrocarbon chains. They are also called subsitituted Hydrocarbon or Branched Hydrocarbons.

Alkyl group is an alkane which has lost one Hydrogen atom and replace by other alkyl group.

Example:

2,2,4-Trimethylpentane

If there have more than one of the same kind of Alkyl group, then use the prefix--"di", "tri"

Example:



Alkyl Groups

Methyl--CH3

Ethyl--CH2-CH3

Proply--CH2-CH2-CH3

Butyl--CH2-CH2-CH2-CH3

Pentyl--CH2-CH2-CH2-CH2-CH3

....

Last but not least, we have two videos that could help you get a better understanding of naming and drawing Alkane hydrocarbon .

May 10-- Electron Dot and Lewis Diagram

Electron Dot diagram is the other name of Lewis Diagram

 - the electrons are represented by dots

Around the nucleus, there are 4 orbitals and each orbital can hold a maximum 2e.We are using dots to represent electrons. The dots are placed on the 4 sides in pairs.

Here is an example.

exercise 1

Draw the electron dot diagram ---HCl

First of all, list up all the valence electrons

Hydrogen 1e

Chlorine   7e

For this question, there is no central atom.The one furthest from a full shell is the central atom.

* we also can use "-" instead or " ."

May.18--Chemical Bonding

First of all, there are three types of chemical bonds: polar covalent bond, non polar covalent bond, and ionic bond.

What are the differences among those three bonds?

A Polar Covalent Bond is formed when the electrons are shared unequally.

A Non Polar Covalent Bond, on the other hand, is formed when the electrons are shared equally.

An Ionic Bond is formed when the electrons are transferred between two atoms.

All chemical bonding is based on the electrostatic relationships.

1. Opposite charges attract each other. 

2. Like charges repel each other.

3. The greater the distance between two charged particles, the smaller the attractive force existing between them. 

4. The greater the charge on the particles, the greater the force of attraction between them.

Note: This force of attraction is called electrostatic force.

But what exactly is the definition of electrostatic force???

- It is a force that exists between charged particles as a result of attraction or repulsion. It operates equally in all directions. (Positivelly-charged particles attract negatively-charged ones from all around it.)

Now, it's time to introduce electronegativity.

Electronegativity is the measure of the tendency of an atom to attract electrons from a neighbouring atom.

Depending on the difference in electronegativity between two atoms, the degree of electron sharing between those two atoms can be different.
So, what does that mean???
Let's look at this periodic table below, which shows a scale called the Pauling Scale.
The scale is used to measure the electronegativity value of each element. It ranges from 0.7 to 4.0.

Atoms with higher electronegativity values are more likely to attract its electrons and electrons from neighbouring atom.
In general, metals have low electronegativity values, and non-metals have relatively higher electronegativity values.


The difference between the electronegativity values of the two bonded atoms determines whether electrons will be shared or transferred.
How to determine the type of bond?

Energy Difference = | ENeg1 - ENeg2 |

- If ENeg Diff. < 0.5, it is a Non-Polar Covalent Bond.
- If ENeg Diff. is between 0.5 and 1.8, it is a Polar Covalent Bond.
- If ENeg Diff. > 1.8, it is an Ionic Bond.

 Non-Polar Covalent Bonds:
- formed when two atoms having less than full shells are able to share their electrons with each other to attain full shell (a very stable arrangement).
- two atoms share electrons EQUALLY

Characteristics of covalent bonds
- also very strong
- have lower melting points than expected 
This is weird. WHY? 

It has something to do with intramolecular and intermolecular forces. 

Intramolecular Forces: are found within a molecule, and are responsible for holding the atoms of a molecule together.

Intermolecular Forces: are found between the molecules, and are responsible for the bonding between molecules.


Now we can explain why covalent bonds have low melting points.
During the melting process, the covalent bonds within each molecule are not affected. The weak bonds (intramolecular forces) are broken instead. Since they are easily broken, the melting points of covalent bonds are relatively low.





Polar Covalent Bonds:

Polarity-a molecule's electrical balance. 
Polar: when there is an imbalance with electrical charge
Non Polar: when the electrical charge is the same strength on all sides of the molecule.


Polar covalent bonds are bonds that contains unequal sharing of electrons.


In a polar covalent bond, the atom with the greater electronegativity value will pull the electrons in the bond more towards itself.


Why is the bond called polar covalent?
- The atom with higher electronegativity will form a Partial Negative charge (between 0 and -1)
- The atom with lower electronegativity will form a Partial Positive charge (between 0 and 1)


We usually use an arrow sign to indicate the migration of electrons (towards the more electronegative atom).

Ionic Bonds:

- metals lose electrons and become positively-charged ions (cations) --> lower electronegativity

- non-metals gain electrons and become negatively-charged ions (anions) --> higher electronegativity

After bonding, the electron arrangement in the ions become very stable (the same as a noble gas).

Characteristics of ionic bonds:
- very strong
- high melting points 
 

Dipole: when one end of a molecule has a slight positive charge and the other end has a slight negative charge, the charge separates partially.

History of Periodic Table

History of Periodic Table

-In the beginning: discover elements 52 by 1817, 62 by 1863

 Some kinds of organizations were needed:

·         First attempt done in 1820’s

·         1857 William Ordling separated the known elements into 13 groups based on their physical and chemical properties. (It was a start)

·         Between 1863 and 1866 John Newlands assigning Hydrogen -mass1 and ordering the known elements by their masses, every eighth element shared a common set of properties

(“Law of octaves”). Weaknesses: cannot predict elements, and he kept changing the orders

·         1869- Dimitri Mendeleev published a method of organizing the elements according to both their masses and their properties. The elements are listed according to masses, certain properties recur PERIODICALLY. (Rows (PERIOD) and columns (GROUP).)

-can accurately predict elements

-chemists can understand and organize data and predict new properties

Modern periodic table

·         Is organized according to atomic number rather than atomic mass.

·         The periodic law summarizes the periodic table. The Periodic Law: Properties of the chemical elements recur periodically when the elements are arranged from lowest to highest atomic numbers

 Period: The set of all elements in a given row going across the table.

Group or Family: The set of all elements in a given column going down the table.

Alkali Metal = elements in the first column (Except H)

Alkaline Earth Metals = The elements in the second column

Halogens = second column from the end on the right hand side. Starting with Fluorine.

Noble Gases = Far right side of the table. Starting with helium.

Lanthanides = elements in the first row shown underneath the table. Starting with lanthanum.

Actinides = underneath the Lanthanides. Starting with actinium.

·         Metals, non-metals, semiconductor

Atomic Structure

Atomic Structure

·         Subatomic Particles

Neutrons- large with no charge

Proton- large with positive charge

Electron- small with negative charge

Name	Symbol	Relative Mass (Atomic Mass Unit, AMU)	Electric Charge	Location in the Atom
Proton	1p 1	1	+1	Nucleus
Neutron	1n 0	Slightly >1	0	Nucleus
Electron	0   e −1	≈0	-1	Cloud surrounding the nucleus

·         In a neutral atom,

Number of protons = Number of electrons (overall charge is 0)

·         Atomic Number = # of protons = # of electrons

·         If a proton is added to an element’s nucleus, a new element will be produced.

For example, O add one proton, atomic mass from 16 to 17, atomic number from 8 to 9

·         Ions- Atoms that gain or lose electrons

Number of electrons = protons – charge

·         Negatively-charged ion (anion): add a electron (electrons more than protons)

·         Positively-charged ion (cation): lose electrons (protons more than electrons)

·         Mass Number (A): is the total number of protons and neutrons or atomic mass number.

Since Atomic Number = The # of protons, Atomic mass = # of protons + # of neutrons

Number of Neutrons = Mass Number –Atomic Number

Atomic Mass ≈ Mass Number

·         Isotopes are atomic species having the same atomic number (protons) but different atomic masses/mass numbers (neutrons).

·         The molar mass represents an average value of a mixture of isotopes.

Example: Cl-35 = 75.77% and Cl-37 = 24.23%

Average mass = (0.7577 x 35) + (0.2423 x 37) = 35.49 g/mol