Sunday, September 04, 2005
CHEMISTRY - Ionic Compounds
~ionic compounds~
properties of ionic compounds
gaint lattice structures
non-volatile
high melting point
high boiling point
ionic bonds are very strong
large amount of energy needed to break up strong bonds
solids at room temperature
---------
usually soluble in water (except e.g. silver chloride and barium sulphate)
- water can seperate the positive ions from the negative ions (thus dissolve)
ionic compounds do not dissolve in organic substances
---------
ionic compounds do not conduct electricity in the solid state
-ions not free to move about
however, it is able to conduct electricity when dissolved in water
-ions are able to move freely in the molten or aqueous state.
============================================
covalent compounds
sharing of electons between atoms
_______________
simple molecular compounds
-----------------
iodine - I2
solid iodine is dark grey
when heated, sublimes to form a purple gas
iodine atoms are held by strong covalent bonds to form iodine molecules
between iodine molecules, they are held by WEAK VAN DER WAALS' FORCES.
-these forces breaks down on gentle heating.
iodine is said to have a simple molecular structure
-----------------
methane - CH4
held by weak van der waal's forces
-exist as gas at room temperature
____________
Giant molecular compound
-----------------
sand - silicon oxide - SiO2
each silicon atom is bonded to four oxygen atoms in a TETRAHEDRAL STRUCTURE
high melting point
high boiling point
all atoms are strongly bonded together
-----------------
diamond - allotrope of carbon
each carbon atom is joined to four other caron atoms by strong coavlent bonds.
TETRAHEDRAL
very hard substance
high melting point
high boiling point
large amount of energy needed to break carbon atoms apart.
diamond cannot conduct electricity
- all valance electrons are used for bonding
- no free electron to move through the structure
-----------------
graphite
flat layers of carbon atoms that lie on top of one another
-layers are held by weak van der waal's forces
within layer, each carbon atoms are held by strong covalent bonds with 3 other carbon atoms.
-thus each layer is a giant molecule.
high melting point
high boiling point
bonds between layers of carbons are very weak, can slide over one another
-soft and slippery
can conduct electricity
- has one valance electron not used to form covalent bonds.
- valacen electron can move fmo one layer to another, hence good conductor.
________________
-properties of covalent substances (simple molecular structure) -
strong covalent bonds
weak van der waal's forces
during heating, molecules do not break up, but move further apart
volatile - low melting and boiling point
(not much heat energy needed to break weak van der waal's forces)
most covalent molecules are insoluble in water (except alcohol and sugar)
some dissolve in water because of chemical reactions (e.g. chlorine)
usually soluble in organic solvents
do not conducr electricity whether in the solid or molten state
- do not contain ions
exceptions : graphite, and hydrogen chloride and hydrogen sulphide when dissolved in water
============================================
metallic bonding - force of attraction between positive ions and the free electrons
metal atoms are held strongly by metallic bonding
in the metal lattice, the atoms lose their outer valance electrons and become positively charged
the valance electrons are DELOCALISED (dont belong to any metal atom)
a lattice of positive ions surrounded by a sea of mobile electrons.
electrons are known as free electrons.
good conductors of electricity
- mobility of the outer electrons within the metal lattice
- free electrons move from negative terminals to the positive
layer of atoms can slide over another
without disrupting the metallic bonding
- strong but flexible
- malleable (hammered into sheets)
- ductile (drawn into wires)
==========================================
properties of ionic compounds
gaint lattice structures
non-volatile
high melting point
high boiling point
ionic bonds are very strong
large amount of energy needed to break up strong bonds
solids at room temperature
---------
usually soluble in water (except e.g. silver chloride and barium sulphate)
- water can seperate the positive ions from the negative ions (thus dissolve)
ionic compounds do not dissolve in organic substances
---------
ionic compounds do not conduct electricity in the solid state
-ions not free to move about
however, it is able to conduct electricity when dissolved in water
-ions are able to move freely in the molten or aqueous state.
============================================
covalent compounds
sharing of electons between atoms
_______________
simple molecular compounds
-----------------
iodine - I2
solid iodine is dark grey
when heated, sublimes to form a purple gas
iodine atoms are held by strong covalent bonds to form iodine molecules
between iodine molecules, they are held by WEAK VAN DER WAALS' FORCES.
-these forces breaks down on gentle heating.
iodine is said to have a simple molecular structure
-----------------
methane - CH4
held by weak van der waal's forces
-exist as gas at room temperature
____________
Giant molecular compound
-----------------
sand - silicon oxide - SiO2
each silicon atom is bonded to four oxygen atoms in a TETRAHEDRAL STRUCTURE
high melting point
high boiling point
all atoms are strongly bonded together
-----------------
diamond - allotrope of carbon
each carbon atom is joined to four other caron atoms by strong coavlent bonds.
TETRAHEDRAL
very hard substance
high melting point
high boiling point
large amount of energy needed to break carbon atoms apart.
diamond cannot conduct electricity
- all valance electrons are used for bonding
- no free electron to move through the structure
-----------------
graphite
flat layers of carbon atoms that lie on top of one another
-layers are held by weak van der waal's forces
within layer, each carbon atoms are held by strong covalent bonds with 3 other carbon atoms.
-thus each layer is a giant molecule.
high melting point
high boiling point
bonds between layers of carbons are very weak, can slide over one another
-soft and slippery
can conduct electricity
- has one valance electron not used to form covalent bonds.
- valacen electron can move fmo one layer to another, hence good conductor.
________________
-properties of covalent substances (simple molecular structure) -
strong covalent bonds
weak van der waal's forces
during heating, molecules do not break up, but move further apart
volatile - low melting and boiling point
(not much heat energy needed to break weak van der waal's forces)
most covalent molecules are insoluble in water (except alcohol and sugar)
some dissolve in water because of chemical reactions (e.g. chlorine)
usually soluble in organic solvents
do not conducr electricity whether in the solid or molten state
- do not contain ions
exceptions : graphite, and hydrogen chloride and hydrogen sulphide when dissolved in water
============================================
metallic bonding - force of attraction between positive ions and the free electrons
metal atoms are held strongly by metallic bonding
in the metal lattice, the atoms lose their outer valance electrons and become positively charged
the valance electrons are DELOCALISED (dont belong to any metal atom)
a lattice of positive ions surrounded by a sea of mobile electrons.
electrons are known as free electrons.
good conductors of electricity
- mobility of the outer electrons within the metal lattice
- free electrons move from negative terminals to the positive
layer of atoms can slide over another
without disrupting the metallic bonding
- strong but flexible
- malleable (hammered into sheets)
- ductile (drawn into wires)
==========================================
# we mugged! @ 2:40 AM 
