2. covalent bonding + charge cloud

Bonding

bond enthalpy

energy needed to break a bond

mean bond enthalpy

average energy needed to break a certain type of covalent bond over a range of compounds

solubility

ionic compounds tend to dissolve in water. water molecules are polar- meaning part of the molecule has a small negative charge and the other part in positive. water molecules pull the ions away from the lattice and cause it to dissolve

molecules

form when 2 or more atoms bond together via covalent bonds

covalent bonds can be…

• single bonds

• double bonds

• triple bonds

single bonds

a single covalent bond contains a shared pairs of electrons to gain a full outer shell

both positive nuclei are attracted electrostatically to the shared electrons

simple covalent compounds

compounds that are made up of lots of individual molecules held by strong covalent bonds,

but the molecules within the simple covalent compounds are held by weak intermolecular forces

intermolecular forces in simple covalent compounds

its the intermolecular forces that determines the properties of simple covalent compounds

so in general they have low melting and boiling points and are electrical insulators

giant covalent structures

a type of crystal structure that has huge networks of covalently bonded atoms AKA macromolecular structures

graphite

the carbon atoms in graphite are arranged in sheets of flat hexagons covalently bonded with 3 bonds each so the 4th outer electron of each carbon atom is delocalised.

the sheets of hexagons are bonded together by weak van der waals forces

property of graphite, weak VDWs between layers:

bonds can be easily broken so the sheets can slide over each other. graphite feels slippery and is used as a dry lubricant and in pencils

property of graphite, delocalised electrons:

free to move along the sheets so an electric current can flow

property of graphite, here is a large distance between the layers of graphite:

so it has a low density and is used to make strong lightweight sports equipment

property of graphite, very high melting and boiling point:

due to strong covalent bonds in hexagon sheets

property of graphite, insoluble in any solvent

because covalent bonds are too strong to break

carbons in diamonds

are arranged in a tetrahedral crystal lattice structure

property of diamond, very high melting points

due to covalent bonds

property of diamond, extremely hard:

due to covalent bonds

property of diamonds, a good thermal conductor:

vibrations travel easily throughout the stiff lattice due to covalent bonds

property of diamond can’t conduct electricity

because all outer electrons are held in localised bonds

property of diamonds, cant dissolve in any solvent

due to covalent bonds

coordinate dative covalent bonds

1 atom provides both shared electrons in a covalent bond

ammonium ion NH₄⁺

nitrogen atom donates a pair of electrons to a proton H⁺

coordinate bonds form when…

… one of the atoms in a bond has a lone pair of electrons and the other doesn’t have any electrons available to share

the hydroxonium ion H₃O⁺

formed when H₂O reacts with H^+, H⁺ has no electrons so can only receive electrons and oxygen in H₂O has 2 lone pair electrons so 1 lone pair is used to form a dative bond with H⁺

WHY DOES CHLORINE HAVE A LOWER BOILING POINT THAN BROMINE?

Chlorine has a lower boiling point than bromine due to its smaller molecular size and weaker van der Waals forces. As a result, it requires less energy to overcome these intermolecular forces.

halogen bond strength

strongest Cl₂>Br₂>F₂>I₂ weakest