Chemical Bonding!

Chemical bonding only involves the valence e-

Formed when e- attracted by nucleus of another

Electrostatic force- opposite charge attract; like charge repel

- greater distance, smaller attraction

- greater charge, greater force.

- the force operates equally in all directions


Intermolecular force=force between molecules

Intramolecular force=force within a molecule

Only weak bonds break in melting process



Chemical bonds exhibit various degrees of sharing, depending on the amount of attraction.



Polarity=molecule's electrical balance, but imbalance with electrical charge of elements



Ionic=electrons are transferred

Non polar covalent=shared equally

- Electronegativity difference <0.5

- Attain full electron shells

- Simultaneously attracted

- high melting points(except CH4, O2, F2)

Polar covalent= shared unequally

- higher energy=partial negative charge=δ-

- lower energy=partial positive charge=δ+

- arrow indicates the migration of electrons

Example

Organic Chemistry May 26, 2011

The chemistry of carbon compounds
.

Importance
-organic compounds are seen anywhere in our life.
-Examples of organic compounds: sugar, chair.......

Properties of organic compounds.
-low melting point
-weak or non-electrolytes
-can forms chains of carbon atoms that are linked in a
①straight-line

 

②circular pattern

③branched pattern

    -can link with other atoms in:

    single bonds

  double bonds

  triple bonds

*Versatility organic compounds makes it such an important branch of chemistry.

Alkanes (unbranched/straight chain)

-A hydrogen : only contains O,H

There are different types of hydrogen

                             ways to present them

-no-polar molecules → immiscible with water

-geometry: tetrahedron

-alkanes are saturated alkanes( all C atoms are bonded by single bonds)

*Saturated: not possible for another atom to bond to the structure.

-Naming of alkanes: the names of all hydrocarbons end in "-ane"

Ex. The structure of C2H6?

①          

     full structure                     

②CH3CH2CH3  

Condensed structure

③C3H8

molecular formula

④

 

Ball-and-Stick model

Names of Alkanes.

methane   CH4

ethane      C2H6

propane   C3H8

butane      C4H10

pentane    C5H12

hexane     C6H14

heptane    C7H16

octane      C8H18

nonane     C9H20

decane     C10H22

They are homologous series: a series of organic compounds with similar general formula, possess similar properties.

CnH(2n+2) -----only for alkanes.

Branched hydrocarbons

hydrocarbons have "side branches" which are also hydrocarbon chains.

(substituted carbon/ branched carbon)

Ex

* Alkyl group: an alkane which has lost one hydrogen atom.

The bottom part are alkyl group(CH3)

 

The name of this branced hydrocarbon is 2-methylpropane

*"-pronpane" is the parent hydrocarbon(longest chain)

Carbon has 4 bonds.

  10 hydrogens

Naming: the names of all alkyl groups end in "-yl", because they are alkyl.

Ex. C2H6      ethyl  C2H5

      C3H8      propyl C3H7

Electron Dot & Lewis Diagrams

- nucleus is represented by the atomic symbol

- for individual elements, # of valence electrons

- electrons are represented by dots around the symbol

- a orbit hold a max of 2 electrons

- each orbital gains 1 electron before pair up

Each bond represents 2 electrons

All valence electron must be used

Each element must have a full valence orbital except H

Ex. CH4

Period Table Trend

Metallic Properties:
- the change from metallic to non-metallic going from left to right across the table
- elements become more metallic going down a family

Atomic Radius:
- Decreases across a row from left to right, increase down a group

Reactivity:
- metal&non-metal show different trend
- most metal: Francium
- most non-metal: Fluorine


Ion charge:
- elements ion charges depend on their group


Melting&Boiling point:
- centre of the table-->highest melting/boiling point
- noble gases have lowest melting point

Ionization Energy
- increases up and right
- hellium highest
- Francium lowest

Electronegativity:
- fluorine has highest electronegativity

- Francium has lowest electronegativity