Alkenes and Alkynes

OH! Why hello there,

I didn't see you come in.

Spoiler alert: this blog post is about alkenes and alkynes

but you probably knew that if you read the title.

but apparently it's cool if I pretend that we all didn't know

I'm sorry! I just want to fit in D:

Alkenes and Alkynes are carbons that can form double and triple bonds with carbon atoms respectively.

They have rules that are almost the same as alkanes (Position of bonds always has the lowest number and is put in front of the parent chain)

Alkenes

• one or more double bonds between carbon atoms
• lead to unsaturated hydrocarbon
• ending changed from -ane for alkanes to -ene for alkenes
• use the same general formula CnH2n

Practice: draw 3-ethyl-2-pentene

                name this alkene

 3-ethyl-6,7-dimethyl-2-octene

• geometric isomers


• molecules that have the same structure but different geometry
• they must be distinguished by giving each a different name based on geometry
• compare groups attached to bonds
• If two adjacent carbons are bonded and have side chains on them 2 possible compounds are possible

• If the larger group is above (RR) or below (HH) the double bond is termed 'cis'
• If the larger groups are diagonal (RH), the double bond is termed 'trans'
  
  

Alkynes

• one or more triple bonds
• ending changes from -ane for alkanes, -ene for alkenes to -yne for alkynes
• general formula is CnH2n-2
• same naming rules but without the cis or trans

Practice: Draw 2,2-dimethyl-3-hexyne.

                 Name this alkyne.

3-hexyne

Ta DAH!

Now would you look at that? We finished a lesson even when I didn't hear you knock!

Here is a work sheet:

Try knocking next time!

...

What? You're back??

and you STILL didn't knock?!

Do this quiz and come back when you can knock on the door politely!

Alkanes

Carbon chains have three patterns
straight
circular
branched

Alkanes are saturated hydrocarbons with only single bonds containing only Hydrogen and Carbon.
The names of alkanes end with ane and have a corresponding prefix with the number of Carbons
1-meth
2-eth
3-porp
4-but
5-pen
6-hex
7-hept
8-oct
9-non
10-dec
These are examples of straight carbon chains



Side branches can be added to the main/ parent chain to form branched chains.
The groups added to main chain are called alkyls.
We will explore alkyls in more detail in our next post

Electronegativity and Polarity

Electrostatic Force
Is a force that exists between charged particles
-Opposite charges attract
-Like charges repel
-The greater the distance between forces => lesser force
-The lesser the distance between forces => greater force
- The force operates equally in all directions


Ionic Bonds
-Electrons are transferred
cations- positive ion
anion- negative ion
Bonds are formed in the shape of crystal lattice
These are very strong bonds and therefore have a high melting point

Covalent Bonds
-electrons are shared
-intramolecular covalent bonds are held together by intermolecular forces (weak)

-Intra forces are found within, they hold atoms of a molecule together (strong)
-Inter forces are forces between molecules (weak)

Electronegativity
-Is the tendency to attract electrons => determines what type of bond will form
- Pauling Scale from 0.7-> 4.0
ENeg difference = abs(ENeg1-ENeg2)
ENeg difference will determine the type of bond formed

Polarity
electrical imbalance=> polar
When ENeg difference is less than 0.5 it is non-polar covalent
When ENeg difference is between 0.5 and 1.8 it is polar covalent
All other ENeg differences are ionic so non-polar

http://www.youtube.com/watch?v=faa5oHr8i8w
http://www.youtube.com/watch?v=Kj3o0XvhVqQ

Lewis Diagrams

Lewis Diagrams are a way of visualizing what is happening in the outermost shell on atoms.
They only show the valance electrons and are therefore handy when dealing with bonding.
Here are a few examples
Covalent


Ionic


Here is a video on lewis and dot diagrams
http://www.khanacademy.org/video/valence-electrons?playlist=Chemistry

Electron Dot and Lewis Diagrams

So for todays class we learned about the Electron Dot and Lewis Structures. It was mainly review with a few minor new things. I will keep this short, and sweet! Enjoy :)

These are a couple of ways you can draw bohr diagrams.....but before i show you, just keep in mind, that when you draw dots on around the symbol of the specific element, you would have to know the number of valence electrons of the required element.

Here's the example.....



This is a breif video about how to make Lewis Structures.

http://www.youtube.com/watch?v=6xTY63KqACE&feature=player_embedded

Here are the steps on making a Lewis Structure;

Draw the atoms on paper and put dots around them to represent valence electrons of the atom. Be sure to have the correct number of electrons.

If the species is an ion, add or subtract electrons corresponding to the charge of the ion. Add an electron for every negative (-) charge, and subtract an electrons for every positive (+) charge.

Consider bonding between atoms by sharing electrons, some may come from one atom.

If possible, apply the octet rule to your structure. Some structures don't obey the octet rule, but explain why.

Assign formal charges to atoms in the structure

Check out this website and try out the problems !

http://misterguch.brinkster.net/PRA017.pdf

History of the Periodic Table

Greetings!

Today we shall be investigating the history of the periodic table!

Excuse me while I grab Micheal J. Foxx for our read today.

In the beginning

Chemists were starting to discover a lot of elements (62 by 1863).

They needed some kind of organization.

William Odling

• in 1857 separated known elements into 13 groups based on their physical and chemical properties

John Newlands

• in 1863 showed that by assigning Hydrogen an arbitrary mass of 1 and ordering known elements by masses, every 8th element shared comment set of properties. (Law of Octaves)
• this failed to predict elements and constantly changed the order the elements

Dimitri Mendeleev

Published method organizing the elements according to their masses and properties

• Showed elements listing according to masses and certain properties recurred periodically 
• broke list into series of rows/periods and columns/groups
• placed elements in certain groups based on properties in spite of contrary indications by its mass

He left gaps in his table, proposing that there where elements yet to be discovered

This allowed chemists to organize, understand data and predict new properties

Modern Periodic Table

Organized by atomic number rather than mass
Periodic Law summarizes the periodic table

• properties of the chemical elements recur periodically when the elements are arranged from lowest to highest atomic numbers

Major divisions of the periodic table are

• periods: set of all elements in a given row across the table
• groups/families: set of all elements in a given column going down the table

Chemical Families

• Metal and NonMetal Properties

• Metalloids
• or semiconductors are non-metals with electrical conductivity that increase with temperature
• have properties resembling metals more than non-metals
• the difference between metals and metalloids is
• metals conductivity decreases with increasing temperature
• metalloids conductivity increase with increasing temperature

Now that you are familiar with the periodic table, let us celebrate with a song!

Trends on the Periodic Table

Greetings lowly visitors

I see you are not up to date on your periodic trends

I scoff in your general direction! Look at that row! It's so last season.

Periodic Trends

• tendencies of certain elemental characteristics to increase or decrease as one progresses along a row or column of the periodic table of elements
• there are several trends that you must be able to describe to be trendy within this circle!
• metallic properties
• atomic radius
• ionization energy
• electronegativity
• reactivity
• ion charge
• melting/boiling point
• density

Metallic Properties

• properties change from metallic to non-metallic from left to right
• become more metallic going down a family in the periodic table

Atomic Radius

• Decrease going across row from left to right
• Increase going down a group
• as the number of protons in the nucleus of the atom increases, there is a greater force of attraction for the electrons in the shell and the distance between the electrons and nuclease decrease

Reactivity

• metals and non-metals show different trends
• when the metals move down and right it is more reactive
• when non-metals move left and up it is more reactive

Ion Charge

•  element charges depend on their group

Melting Point and Boiling Point

• elements in the centre of the table have the highest melting point
• noble gases have the lowest melting point
• start from the left and moving right; melting point increases until the middle of the table

Ionization Energy

• the energy needed to completely remove an electron from an atom
• increases going up and to the right
• all noble gases have ionization energy
• helium has the highest ionization energy and francium has the lowest
• opposite trend from the atomic radius
• measured in KJ/mol
• can have 1st ionization energy, 2nd ionization energy
• refer to the removal of more than one electron

Electronegativity

• refer to how much atoms want to gain electrons
• same trend as ionization energy
• tendency of an atom to attract electrons from a neighboring atom
• if atom has high EN
• strongly attract electrons and may completely remove them
• also strong attracted to own valence electrons=harder to remove
• if atom has low EN
• little tendency to remove electron from neighbor
• also has small attraction to own electrons
• low ionization energy=easily removable

VOILA! NOW AREN'T YOU ALL FANTABOULOUS READERS?!

LOOK AN INTERACTIVE PERIODIC TABLE

Learn from it! Understand it!