Chemical Compounds
Properties of Molecular and Ionic Compounds
Molecular Compounds
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formed from only non-metallic elements
does not form ions in solution
usually does not conduct electricity
solid, liquid or gas at room temperature
bonds formed by sharing of electrons
bonds between atoms are strong, but
between molecules are weak
Ionic Compounds
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formed from metallic & non-metallic elements
forms ions in solution
conducts electricity
solid at room temperature
bonds formed by exchange of electrons
bonds are very strong until compound is
dissolved in water – then very weak
CHEMICAL BONDS
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elements are held together by chemical bonds
chemical bonds are formed when elements gain, loose or share electrons
if the elements are gaining or loosing electrons then an IONIC COMPOUND is
formed
if the elements are haring electrons then a MOLECULAR COMPOUND is formed
MOLECULAR COMPOUNDS
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made up of NON METALS which are bonded by the sharing of electrons
MOLECULE
– a clusters of atoms joined together
– the smallest unit of a pure substance
– the bond between atoms is very strong… atoms stay linked no matter how many
times substance changes state (frozen, melted or boiled)
– e.g. O, C, H, N
DIATOMIC MOLECULE
– molecules made of 2 atoms of the same element
– the bond between atoms is very strong… atoms stay linked no matter how many
times substance changes state (frozen, melted or boiled)
e.g. H2, C2, O2, N2
–
BINARY MOLECULAR COMPOUNDS
– molecular compound made from 2 different elements
– the bond or attraction between molecules is weak... elements will tend to break
apart when they change state → so if you boil water the gas you get will be oxygen
and hydrogen (not H2O gas)
– e.g. H2O, CO2
Naming Molecular Compounds – Symbol to Words
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if you see the chemical formula in symbols you can change it to words by using the
following rules:
1. 1st symbol - write down the elements full name
2. 2nd symbol - start with the elements name, then change it by adding “ide”
3. both symbols - use a prefix to indicate the number of each type of atom in the
formula
(note: mono is only used for the 2nd element)
1 – mono
5 – penta
9 – nona
2 – di
6 – hexa
10 – deca
3 – tri
7 – repta
11 – unda
4 – tetra
8 – octa
12 – dodeca
examples:
CO – carbon monoxide
CO2 – carbon dioxide
NF3 – nitrogen triflouride
CCl4 – carbon tetrachloride
N2O – dinitrogen oxide
N2O3 – dinitrogen trioxide
Naming Molecular Compounds – Chemical Formula
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the chemical formula uses symbols and numerals to represent the composition of
the pure substance
if you are given the written name of the molecular compound you can figure out its
chemical formula by using the following rules:
1. write down the symbols for the elements in the order they appear
2. if there are any prefixes then add the number they represent as a
subscript to the appropriate element
examples:
sulfur dioxide – SO2
phosphorus tetrachloride – PCl4
dinitrogen hexabromide – H2Br6
Molecular Compounds with Hydrogen
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molecular compounds with H, and a few others, are know by their common names
for example:
o water – H2O
o sugar – C12H22O11
o ammonia – NH3
o acetic acid (in vinegar) – C2O2H4
o methane – CH4
o hydrochloric acid – HCl
o ethane – C2H6
o hydrogen peroxide – H2O2
o benzene – C6H6
o laughing gas (nitrous oxide) – N2O
IONIC COMPOUNDS
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made up of a METAL and a NON METAL which are bonded by the exchange of
electrons – one element gains an electron and one element looses an electron
ION
– when an atom gains or looses electrons it is no longer neutral (i.e. # protons does
not equal # neutrons) → it becomes an ion
– protons have a positive charge and electrons have a negative charge – so if an
element looses an electron it will have a positive charge and if it gains one it will
have a negative charge
– it is possible for an element to gain or loose more than one electron
– an ion is a particle or group of particles with a positive or negative charge
– e.g. Na+ or ClPOLYATOMIC ION
– some atoms act as a group and give or receive one or more electrons (e.g. CO 32-)
BINARY IONIC COMPOUNDS
– ionic compounds made from 2 different elements → a metal and a non metal
– the bond or attraction between ions is very strong when elements are solid;
and very weak if they are placed in water and dissolve
– e.g. NaCl, CaCl2
Naming Ionic Compounds – Symbol to Words
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if you see the chemical formula in symbols you can change it to words by using the
following rules:
1. 1st symbol (the metal) – write down the elements full name
2. 2nd symbol (the non metal) - start with the elements name, then change it by
adding “ide”
examples:
NaCl – sodium chloride
CaCl2 – calcium chloride
Mg3N2 – magnesium nitride
Naming Ionic Compounds – Words to Symbols
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if you are given the written name of the molecular compound you can figure out its
chemical formula by using the following rules:
1. write down the symbols for the elements in the order they appear – the metal
will always be first and the non metal second
2. use subscripts to show the ratio of ions in the compound – remember that the
net charge of the chemical formula must be zero
e.g. CaCl2 has a ratio of Ca to Cl ions of 1:2 because the ionic charge of Ca
is 2+ and the ionic charge of Cl is 1- → when the compound is formed the net
combined charge must be zero so 2 negatively charged chlorine atoms are
needed to balance a single positively calcium atom with a 2+ charge
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examples:
potassium iodide – KI (ratio is 1:1, K1+ and I1-)
aluminum oxide – Al2O3 (ratio is 2:3, Al3+ and O2+)
barium chloride – BaCl2 (ratio is 1:2, Ba2+ and Cl1-)
Why do some elements have more than one ionic charge shown on the periodic
table?
 some elements have more than one ion charge → e.g. Fe, Cu, Pb
 in order to show clearly which ion is being used in the chemical formula a Roman
numeral is added in brackets behind the metal e.g. iron (II) oxide is a compound
containing Fe2+ and iron (III) oxide is a compound containing Fe3+
 when you are looking at the formula you can tell which ion is being used by looking
at how many atoms of each element are present
 examples:
iron (III) oxide
Fe2O3
copper (II) phosphide
Cu3P2
lead (IV) fluoride
PbF4
Showing the State of the Compound
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the state of the compound (solid, liquid or gas) is shown by a subscript symbol in
brackets after the compound symbol:
(s) = solid
(l) = liquid
(g) = gas
(aq) = aqueous
e.g. H2O (l)
HBr (g)
aqueous means that the compound is dissolved in water and therefore it is present
as a solution