ChemistsOnline*

intermolecular forces

there are 3 types

van der walls which is the weakest ,dipole dipole, hydrogen bonding which is the strongest

van der walls

they act between all molecules
all atoms of molecules have positive and negative charges
these charges will produce very weak electrostatic forces between the molecules and the atoms
these electrostatic forces are called van der walls forces
in any atom the electrons can be anywhere at any time , at an instant both electrons can be together at one time on one side this becomes slightly negative and is called a temporary dipole , because these electrons will keep moving and reoccurring
the atom with the temporary dipoles will induce dipoles that are in near by atoms by attracting the positive nucleus
this will be called instantaneous dipole and induced dipole forces
the dipoles are caused by changing the position of the electron cloud
the size of the van der walls forces increases as the size of the atom increases and the number of electrons available in the atom increases
as the number of electrons increases the melting and boiling point increases , because more electrons are there which means there are more van der walls forces

common questions :

why is hexane a liquid at room temp and butane is a gas?

because the carbon chain is longer

dipole dipole forces

only occur in molecules that have a polar bond
in CO2 the dipoles cancel out
dipole dipole are permanent and act between electronegative atoms
the more the electronegative the atom is the stronger the electrostatic attraction will be which will make the atom pull electrons closer towards itself, this will lead to creating a delta negative side and a delta positive side
molecules can attract similar molecules by filliping over to attract them so each side will be attracted to the opposite charge

molecules like H2 or O2 cant have dipole dipole forces because they are permanent and the atoms are the same

hydrogen bonding

this is the strongest type of forces and it only occurs in FON - fluorine , oxygen and nitrogen covalently bonded to hydrogen

hydrogen bonding only forms when one of the atoms is electronegative with a lone pair of electrons
this is an example of the bonding in water where the oxygen is more electronegative that hydrogen and it has a lone par of electrons
they are dipole dipole forces but they are much stronger due to having a lone pair and the hydrogen atoms are very small and very electron deficient , the protons are exposed. the lone pair of electrons on the electronegative oxygen on one water molecule is strongly attracted to the electron deficient hydrogen of another water molecule

TO FORM A HYDROGEN BOND WE NEED:

a hydrogen bonded to an electronegative atom so that the hydrogen has a partial charge
an electronegative atom with a lone pair which will attract to the elctron deficient H forming a LINER BOND

BONDING

there are 4 trypes of bonding

1) ionic: is the result of electrostatic attraction between oppositely charged ions

happens between a metal and a non metal
metals lose the electrons and non metals gain it
metals can lose up to 3 electrons at a time depending on their group in the periodic table
when metals atoms lose an electron they become positive ions (cations)
when non metal atoms gain an electron they become a negative ion (anion)
the two oppositely charged ions attract and the electrostatic forces hold them together
the attraction between all positive and negative ions is formed there fore a GIANT LATTICE is formed

properties

cannot conduct electricity unless its molten or in an aqueous state so the ions can move around carrying current
solid at room temp due to its giant lattice
high melting point because lots of electrostatic forces has to be over come
not malleable or ductile or strong
there always a neutral charge over all like NaCl or NaOH

covalent bonding: shared pair of electrons between two non metals

properties

low melting and boiling points because their intermoleucler forces are weak
covalent bonds between atoms are not broken because breaking them will change their properties
they are bad conductors of electricity because molecules are neutral due to the fact they don't have any charges

metalic bonding: is the bonding between the positive metals and the sea of delocalised electrons

occur between atom of one metal
metals can lose up to 3 electrons and become a positive ions
the lost electrons join the sea of delocilised electrons , which has a negative charge
the positively charged ions are attracted to the sea of deloclised electrons
metallic bonds spreads out creating a giant lattice

PROPERTIES

good at conducting electricity : because free electrons can move around carrying current
strength depends on the nuclear charge , as the nuclear charge increases there are more electrons in the sea of deloclised electrons s ,therefore there is more attraction , the smaller the ions thee closer the electrons are pulled to the nucleus and the stronger the structure becomes.
malleable and ductile because when a blow is given the positive ions are still surrounded by electrons and the bonds are not broken
high melting and boiling points because there is a strong attraction between the electrons and positive ions and this extends through the whole lattice.

Dative bonding

this is when both electrons in the shared pair come from one atom EG ammonium
ammonia is made up of nitrogen sharing 3 covalent bonds with 3 hydrogen because nitrogen is in group 5 and it will need 3 more electrons to complete its outer shell to become fully stable.
one of the outer pair of electrons on nitrogen is a lone pair
this lone pair attracts positive hydrogen which has no electron
the dative bond is shared between the lone pair on nitrogen and the positive hydrogen
the over all charge is +