Post on 18-Jan-2016
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Inter-molecular forces
Inter-molecular forces
Works based on
Molecular Geometry
Molecular Geometry
Bonding types & Structures
Bonding types & Structures
Determined by
Determined by
Types of Bonds
Why atoms bond
Atoms are most stable when their outer shell of electrons is full
Atoms bonds to fill this outer shellFor most atoms, this means having 8
electrons in their valence shellCalled the Octet Rule
Common exceptions are Hydrogen and Helium which can only hold 2 electrons.
One way valence shells become full
Na-
-
- --
-
-- - -
Cl-
-
- --
-
-- - -
-
-
-
--
-
-
Sodium has 1 electron in it’s valence shell
Chlorine has 7 electrons in it’s valence shell
Some atoms give electrons away to reveal a full level underneath.
Some atoms gain electrons to fill their current valence shell.
-
One way valence shells become full
Na-
-
- --
-
-- - -
Cl-
-
- --
-
-- - -
-
-
-
--
-
-
-+ -
The sodium now is a cation (positive charge) and the chlorine is now an anion (negative charge).
These opposite charges are now attracted, which is an ionic bond.
Ionic Bonding—Metal + Non-metal
Metals tend to lose their electrons and non-metals gain electrons
Metals become cations (positively charged)Non-metals become anions (negatively charged)The cation & anion are attracted because of
their charges—forming an ionic bond
Bonding between non-metals
When two non-metals bond, they share electrons
Non-metals that share electrons evenly form non-polar covalent bonds
Non-metals that share electrons un-evenly form polar covalent bonds
Metals bonding
Metals form a pool of electrons that they share together.
The electrons are free to move throughout the structure—like a sea of electrons
Atoms aren’t bonded to specific other atoms, but rather to the network as a whole
Type of bond
Electrons Melting/ Boiling Point
Solubility
Electricity Example
Ionic
Polar Covalent
Non-Polar Covalent
Metal
Bond type affects properties
The type of bonding affects the properties of the substance.
There are always exceptions to these generalizations (especially for very small or very big molecules), but overall the pattern is correct
Melting/Boiling Points
Ionic bonds tend to have very high melting/boiling points as it’s hard to pull apart those electrostatic attractionsThey’re found as solids under normal conditions
Polar covalent bonds have the next highest melting/boiling pointsMost are solids or liquids under normal conditions
Non-polar covalent bonds have lower melting/boiling pointsMost are found as liquids or gases
Solubility in Water
Ionic & polar covalent compounds tend to be soluble in water
Non-polar & metallic compounds tend to be insoluble
Conductivity of Electricity
In order to conduct electricity, charge must be able to move or flow
Metallic bonds have free-moving electrons—they can conduct electricity in solid and liquid state
Ionic bonds have free-floating ions when dissolved in water or in liquid form that allow them conduct electricity
Covalent bonds never have charges free to move and therefore cannot conduct electricity in any situation
Copy this table
Type of bond
Electrons Melting/ Boiling Point
Solubility
Electricity Example
Ionic Transferred from Cation to Anion
High: Hard to pull electrostatic attractions
High High when in water or in a liquid
Any type of Salt
Polar Covalent
Share Electrons unevenly
High High Poor Water
Non-Polar Covalent
Share Electrons Equally
Low Insoluble Poor Methane Gas
Metal Sea of Electrons
Depends on metals
Insoluble Excellent Bronze (Iron and Copper Alloy)