Transcript KS4 Ionic Bonding ppt

CHEMICAL BONDING
PART 1
IONIC BONDING
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Elements
• Elements are the simplest substances.
There are about 100 different elements
• Each elements has just one particular
type of atom that is different to the
atoms in any other element
S
Fe
N
O
K
• In some elements atoms bond to form
small simple structures.
• In other elements atoms bond into giant
structures with millions of atoms.
N
N
N
• Even in elements atoms usually join
(bond) together.
N
N
C
N
N
N
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Compounds
• Compounds are formed when
different elements chemically react
together.
• In these reactions different types of
atom become chemically bonded.
• Like elements some compounds
have small simple structures with
just a few atoms bonded together
• Other compounds have large,
complex structures containing
thousands or even millions of
bonded atoms.
H
O
H
Water – a simple
structure
DNA – a large &
complex
structure
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Compounds are not just mixtures
• Reacting is different to just mixing.
• The physical and chemical properties of compounds are
very different to their original elements.
ELEMENTS
Carbon
C
(black solid)
+
oxygen
O O
(colourless gas,
that supports
combustion)
COMPOUND
Carbon dioxide
O C O
(a colourless gas, that
extinguishes fire)
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Activity
Copy the Table and fill in the last column.
Name
Sodium chloride
Nickel
Copper sulphate
Water
Oxygen
Rust
Mercury
Sand
Formula
Element or
compound
NaCl
compound
Ni
element
CuSO4
compound
H2O
compound
O2
element
Fe2O3
compound
Hg
element
SiO2
compound
Rust
consists of
iron
combined
with
oxygen
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Bonding and atoms
To understand bonding we must know a little about
the atoms from which elements are made.
Atoms consist of three types of particles that are even
smaller than atoms:
–Protons } These exist in
–Neutrons } the nucleus.
–Electrons }
exist in layers (or shells) around the
outside of the nucleus
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No charge on element atoms
Two of the three particles in atoms have an electrical charge.
Protons
+1
Neutrons
0
Electrons -1
BUT atoms have equal numbers of protons and
electrons. This means their overall charge = zero.
For example
19
20
F
Ne
9
10
Fluorine
Neon Copy & Fill in the gaps
9 protons
9+
10+
10 protons ___
___
9 electrons
9-
10 electrons ___
10___
10 neutrons 0
0
10
___neutrons
___
Total Charge 0
Total Charge ___0
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Noble Gases: full shells
The electrons around the outside of
atoms are arranged in layers called
shells
st
2nd Shell:
8 electrons
1 Shell:
2 electrons
3rd Shell:
8 electrons
Each shell has a maximum number of
electrons that it can hold.
In noble gases the shells are completely full rather
than partially full.
During bonding other atoms try to attain the “full
electron shell” structure of the noble gases.
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Types of bonding
Atoms can be joined together in
3 possible ways
Metal and
non-metal
Ionic Bonding
Non-metals
only
Metals only
Covalent Bonding Metallic Bonding
All three types involve changes in the electrons in
the outermost electron shells of the atoms
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IONIC BONDING
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IONIC BONDING
Most ionic compounds contain a metal and a non-metal.
When metals react they lose outer shell electrons to
leave a full electron shell.
This produces a charged atom (ion) with a + charge.
Lose 1 or more
electrons
Neutral atom
n+
Positive ion
When non-metals react with a metal they gain
electrons to achieve a full electron shell.
Gain 1 or more
electrons
Neutral atom
n-
Negative ion
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Opposites attract – lattices
The oppositely charged ions are attracted into a
lattice that gets bigger and bigger until it consists
of millions of ions
+
+
+
+
+
-
-
-
+
-
+
-
+
-
+
attract
-
opposites
+
+
-
And ion, and
ion, and ion!
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Lattices are 3-Dimensional
We have shown ions attracting and
building into a 2 dimensional sheet.
In fact the whole process will be
going on in three dimensions to
build up a giant 3-D lattice.
And so on to
build a giant 3D lattice with
millions of
ions.
-+ +- -+ +- -+ +- + - + - +
+ -+ + -+ + -+
-+ - -+ - -+ -+ +- -+ +- -+ +- + - + - +
+
-
+
-
+
-
+
-
+
+
- +- + - +
- + + - -- +
+ -- ++ -+ +- -+
+
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Ions and electron structures
Metals lose electrons to form
positive(+) ions called cations.
Non-metals gain electrons to form
negative (–) ions called anions.
n+
n-
We know that the atoms lose or
gain electrons to achieve full
electron shells.
To understand more about how
ionic compounds form we must
look at what is happening to the
outer shell electrons.
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Formation of sodium chloride
1. Formation of sodium ions
Sodium has 1 electron in its outer shell.
If it loses this it will have no partially filled shells.
Na
Sodium atom (2.8.1)
Loses 1
electron
Na+
Sodium 1+ ion (2.8.0)
This only happens if there is another atom able to
accommodate the lost electron.
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Formation of sodium chloride
2.Formation of Chloride ions
Chlorine has 7 electrons in its outer shell.
If it gains 1 electron it can achieve a full outer electron
shell. It is, therefore, going to be able to accept the
electron that the sodium wants to lose.
Cl
Cl
Gains 1 electron
(from sodium)
Chlorine atom (2.8.7)
Chlorine I - ion (2.8.8)
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Formation of Sodium Chloride- the overall process.
Sodium loses its
outer electron.
Chlorine gains it.
The result is
both end up with
full shells
Two oppositely
charged ions
are formed,
which attract.
Millions of such
pairs form a
giant lattice
Na
Na
Cl
Cl
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Simpler electron diagrams
We can assume full inner electron shells.
We can therefore sometimes shorten bonding diagrams
by omitting to draw the inner electron shells.
Na
Cl
Na
Cl
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Bonding in Magnesium Oxide
More than one electron may be transferred
between atoms in ionic bonding.
Mg
2.8.2.
Magnesium
atom
O
Magnesium Oxide
2.6
Oxygen
atom
O2-
Mg2+
2.8
2.8
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Draw a simplified bonding diagram (omitting
inner shells) for magnesium oxide.
Mg
O
Magnesium Oxide
Magnesium
atom
Oxygen
atom
Mg2+
O2-
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Copy the diagram and draw another box showing
the electron configuration in sodium fluoride.
Na
2.8.1.
Sodium
atom
F
Sodium Fluoride
2.7
Fluorine
atom
F-
Na+
2.8
2.8
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Bonding in Lithium Oxide
The bonding in lithium oxide is more complicated in that
there are different numbers of each atom.
Li
O
Li+
Li
O2-
Li+
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Bonding in Lithium Nitride
The bonding in lithium nitride similarly involves different
numbers of each atom.
Li
Li
N
Li
Li+
Li
Li+
N3-
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Bonding in Aluminium Fluoride
In aluminium fluoride it is the non-metal atoms that
we need more of.
F
F
F
F
Al
F
Al
F
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Activity
1.
2.
3.
4.
5.
Following the previously shown slides draw bonding
diagrams for the compounds formed from the
following atoms:
Lithium (2.1) and fluorine (2.7)
Sodium (2.8.1) and sulphur (2.8.6)
Magnesium (2.8.2) and sulphur (2.8.6)
Magnesium (2.8.2) and fluorine (2.7)
Aluminium (2.8.3) and nitrogen (2.5)
Remember that the total number of
electrons lost by the metal must equal
the total number of electrons gained by
the non-metal
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Electrons Lost = Electrons Gained
Both sodium chloride and magnesium oxide are simple
ionic compounds.
In both cases the metal and non-metal need to lose or
gain the same number of electrons respectively.
Na
1 electron
Mg
Cl
Na+
Cl-
O
Mg2+
O2-
2 electrons
This is not always the case.
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Different numbers of electrons
Consider the reaction of sodium with oxygen.
– Sodium (2.8.1) needs to lose 1 electron.
– Oxygen (2.6) needs to gain 2 electrons
This can only happen if there are two sodium ions formed
for every one oxygen ion formed.
Na
Na+
1 electron per
sodium
O2-
O
Na
Na+
The formula will be Na2O.
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Different numbers of electrons
Consider the reaction of magnesium with chlorine.
– Magnesium (2.8.2) needs to lose 2 electron.
– Chlorine (2.8.7) needs to gain 1 electrons
We need 2 chlorines for every one magnesium.
Cl
Mg
ClMg2+
2 electrons
Cl
Cl-
The formula will be MgCl2
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Charges on ions
• When atoms form ions they aim to attain electron
shells that are either completely full or completely
empty.
• If we know the electron configuration of an atom we
can usually work out how many electrons it must lose
or gain to achieve a noble gas configuration.
• This will tell us the charge on its ion.
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Charges and Metal ions
• Metals usually lose electrons to empty this outer shell.
• The number of electrons in the outer shell is usually
equal to the group number in the Periodic Table.
For example,
Li
2.1
Li+
Mg
2.8.2 
Mg2+
Al
2.8.3 
Al3+
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Charges and non-metal ions
• Outer shells with 5 or more electrons usually gain
electrons to fill up the outer shell.
For example,
• Oxygen (2.6) gains 2 electrons to form O2• Chlorine (2.8.7) gains 1 electron to form Cl-
O
2.62.8
O  O2-
Cl
2.8.7 2.8.8
Cl  Cl© Boardworks Ltd 2003
Activity
Copy out and fill in the Table below showing what charge
ions will be formed from the elements listed.
H
He
Li Be
B C N O F Ne
Na Mg
Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Symbol
Li
N
Cl
Ca
K
Al
O
Br
Outer
electrons
1
5
7
2
1
3
6
7
1
8
Charge
1+
3-
1-
2+
1+
3+
2-
1-
1+
0
Na Ne
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The formulae of ionic compounds
This is most quickly done in 5 stages.
Remember the total + and – charges must =zero
For example, the formula of calcium bromide.
1.
2.
3.
4.
5.
Symbols:
Charge on ions
Need more of
Ratio of ions
Formula
Ca
2+
Br
1Br
2
1
CaBr2
Br-
Br
Ca2+
Ca
Br
Br-
2 electrons
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The formulae of ionic compounds
For example, the formula of aluminium bromide.
1.
2.
3.
4.
5.
Symbols:
Charge on ions
Need more of
Ratio of ions
Formula
Al
3+
Br
1Br
3
1
AlBr3
Br-
Br
Al
Br
3 electrons
Br
Al3+
BrBr-
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The formulae of ionic compounds
For example, the formula of aluminium oxide.
1.
2.
3.
4.
5.
Symbols:
Charge on ions
Need more of
Ratio of ions
Formula
2e-
Al
Al
3+
O
2O
3 (to give 6 e-)
2
Al2O3
O2-
O
Al3+
2e-
Al
O2-
O
Al3+
2e-
O
O2-
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Activity
Using the method shown on the last few slides, work
out the formula of all the ionic compounds that you can
make from combinations of the metals and non-metals
shown below:
•Metals:
Li Ca Na Mg Al K
•Non-Metals:
F O
N
Br
S
Cl
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More Complicated Formulae
•
•
Ionic compounds may contain ions consisting of
groups of atoms rather than a single atom.
Here are some more complicated ions you may
come across.
Ion
Formula
Charge
Atoms present
nitrate
sulphate
NO3SO42-
12-
N
O
O
O
S
O
O
O
O
ammonium
NH4+
1+
N
H
H
H
H
hydroxide
OH-
1-
O
H
carbonate
CO32-
2-
C
O
O
O
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More Complicated Formulae
•
•
•
When working out formula you simply treat the entire
group of atoms as though it were a single atom.
The only difficulty is to do with how we write down the
final answer.
For example, what is the formula of lithium nitrate?
1.
Symbols:
Li
NO3-
2.
Charge on ions
1+
1-
3.
Need more of
4.
Ratio of ions
5.
Formula
neither
1
1
LiNO3
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More Complicated Formulae
•
What is the formula of magnesium nitrate?
1.
Symbols:
Mg
NO3-
2.
Charge on ions
2+
1-
3.
Need more of
4.
Ratio of ions
5.
Formula
NO3-
1
2
Mg(NO3)2
•
The brackets around the NO3- ion show that the 2 refers
to two complete NO3- ions.
•
It represents a total of 2 nitrogens and 6 oxygens with
each magnesium ion.
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More Complicated Formulae
•
What is the formula of sodium sulphate?
1.
Symbols:
Na+
SO42-
2.
Charge on ions
1+
2-
3.
Need more of
4.
Ratio of ions
5.
Formula
Na+
2
1
Na2SO4
•
No brackets here as only one SO42- ion needed.
•
Note although Na contains 2 letters it only represents a
single atom – so no brackets!
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Write down how to work out the formula of
aluminium hydroxide.
1.
Symbols:
2.
Charge on ions
3.
Need more of
4.
Ratio of ions
5.
Formula
Al3+
OH-
3+
1OH-
1
3
Al(OH)3
Again we need brackets as 3 complete OH- ions are needed meaning
that for each aluminium there are 3 oxygens and 3 hydrogens.
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Write down how to work out the formula of
ammonium sulphate.
1.
Symbols:
NH4+
2.
Charge on ions
1+
3.
Need more of
NH4+
4.
Ratio of ions
5.
Formula
SO42-
2
2-
1
(NH4)2SO4
Again we need brackets as 2 complete NH4+ ions are needed meaning
that for each sulphate ion there are 2 nitrogen and 8 hydrogens.
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Write down how to work out the formula of
aluminium sulphate.
1.
Symbols:
2.
Charge on ions
3.
Need more of
Need to get total
charge =6
4.
Ratio of ions
2
5.
Formula
Al3+
SO42-
3+
2-
3
Al2(SO4)3
No brackets for Al as only one atom even though it’s 2 letters.
We do need brackets around the SO4 to show it is 3 complete sulphate ions.
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Copy this choosing words from below to
fill the gaps.
lose
electrons
•
•
•
•
•
lattices
gain
metal
metal and non-metal react.
Formed when a _____
lose electrons to empty their outer
Metals ___
electron shell.
gain electrons to fill their outer
Non-metals _____
electron shell.
The ratio of metal ions to non-metal ions will
electrons lost
depend upon the number of ________
and gained.
lattices.
The ions formed join up into giant _____.
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Which of the following will have ionic bonding?
A. Copper chloride
B. Iron
C. Brass
D. Sulphur dioxide
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Which of the following is NOT true of ionic
bonding?
A.
B.
C.
D.
Metal ions have a + charge
Non-metal ions have a - charge
They form a 2 dimensional lattice
They have giant structures
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Which of the following is true about the oxide ion?
A.
B.
C.
D.
Formed by oxygen atoms losing 2 electrons.
Oxygen ions have an empty second shell
Exist in pairs
Have a 2- charge
16
O
8
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Which of the following is true about the sodium ion?
A.
B.
C.
D.
Has a 2,8,1 electron arrangement
Formed by sodium atoms gaining 1 electron.
Sodium ions have an empty second shell
Have a 1+ charge
23
Na
11
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What formula compound will be formed from
Mn4+ and O2- ions?
A.
B.
C.
D.
Mn2O4
MnO2
Mn2O
MnO4
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What formula compound will be formed from
Ga3+ and SO42- ions?
A.
B.
C.
D.
Ga2(SO4)3
Ga3(SO4)2
Ga2S3O12
Ga (SO4)3
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