when non-metallic elements it is not energetically
favourable to form ions eletrons are shared between
tthe atoms of the elements in these compunds
when two pairs of electrons form covalent bond
it's called a double bond
dative bond
carbon monoxide has a tripple bond. two pairs are formed by the
carbon and oxygen atoms contributing one electron to the
pair.however both electrons in the third pair come from oxygen
atom. this is called a dative bond
covalent intermolcular bonds within simple molcules like water are strong , however the
electrostatic attractions between simple molcules are weak, this means that small amounts
of energy is needed to seperate one molecule from another
elements and compunds with a simple structure have low melting and boiling pointsbeacuse there is no charged particles
and simple covalent structutres do not conduct electricity they mostly do not dissolve in water
shape of molecules
electron pair repulsion
in methane there is 4 electrons groups attached to
the carbon because similar charges repel they
arrange themselves so that they can be the furthest
away from each other
the furthest they can get apart from each other is 109 degrees apart. this means it is tetrahedral
all carbons surrounded by four single bonds have tetrahedral
arrangement
lone pairs
molecules such as ammonia and water have lone pairs in the outer shells of nitrogen
and oxygen, the lone pairs repel the electron pairs in ammonia and water adopt a
tetrahedral shape. but one or more lone pairs are in the conners.
the simple rule for covalent molecules is that groups of
electrons on the outer shell repel each other and move apart
as far as each other
lone pairs repel more strongly than electrons involved in bonding
other shapes
linear molecules
there are two groups of electrons around the central atom because there is
fewer molecules they can go further apart, the furthest they can get apart is
180 degress.
planar molecules
there are three groups around the central atom, the bond angle is 120 degrees it
is flat and shaped like a triangle is described as a triangular planar
bipyramidal molecules
five groups of electrons around a central atom gives us a trigonal bipyramidal
shape.with electrons at the five corners of the shape.bond angles are about 120
or 90 degrees depending on their position
octahedral molecules
six groups of electrons around a central atom where electrons are directed to the corners of an octahedron
amount of substance
relative atomic mass
amount of moles=mass/molar mass
moles of formula units
amount in moles of formula units=mass/molar mass
Avogardro's constant
is 6.02x10^23
percentage yield
this reduce the amount of product produced
loss of production from reaction vessels , particularly if there are several stages,side reactants occuring ,unwanted product
impurities in reactants,changes in temperature a pressure,if the reaction is an equilibrium system
group one and two have only one
or two outer shell electrons these
get taken away to form cations
non-metal have more than 3 outer shell electrons
they are able to gain electrons and to form
negatively charged ions called anions
having a doubly charged anion is hard because the charges
are both negative and getting a -3 anion is extremely
difficult and hardly happens
cations with 4+ are very unknown
ionic bonding
when metals react with nonmetals ions are
formed if the overall charge is favorable
the cations and anions formed are held together by their opposite
charges in a electrostatic bond
in a compound the ions attract many of the opposite charges creating a giant lattice
ionic salts
acid + alkali= salt + water
acid + base =salt + water
acid + carbonate= salt + water + c02
acid + metal= salt + hydrogen
ionic substances in solution
many ionic substances dissolve in water
the ionic substances that don't dissolve
barium,lead,calcium silver sulphates
silver and lead halides ( chlorides, bromides iodies)
metal hydroxides apart from group one hydroxides and amonimum hydroxide
the ions become surrounded by the water and spread out through
the solution . once they are seperated from each other they are
independant of each other.
the presence of the hydrated ions explain why aquesous solution of salts can conduct electricity
ionic equations
most reactions happen to only have two types of ion
e.g if you have a solution of silver nitrate to a solution of
sodium chloride you get a white percipitate of silver
chloride
the na and the no3- is not involved in the reaction therefore is not put into the
equation they are called spectator ions
bonding,structure and properties
ionic bonding
they are normally solids at room temperature and pressure,and
have lattice structures that consist of negative and positive ions in
al 3 demensions
because of this they form regularly shaped crystals
the electrostatic attractions are strong this is why
ionic compounds have high melting points, once
melted the ions are free to move and can conduct
electricity.
metallic bonding
metals have a lattice structure, the most
important characteristic is the electron sea
model
the model is pictured as a giant lattice structure of metal cations in a
sea of delocalised electrons.