© Boardworks Ltd 2003 CHEMICAL BONDING PART 1 IONIC BONDING.
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Transcript of © Boardworks Ltd 2003 CHEMICAL BONDING PART 1 IONIC BONDING.
© Boardworks Ltd 2003
Elements
• Elements are the simplest substances. There are about 100 different elements N
S
OC
Fe
K
NN
N
N
N N
NN
• Each elements has just one particular type of atom that is different to the atoms in any other element
• Even in elements atoms usually join (bond) together.
• In some elements atoms bond to form small simple structures.
• In other elements atoms bond into giant structures with millions of atoms.
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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.
OH 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
veryvery different to their original elements.
Carbon + oxygen Carbon dioxide
COMPOUNDELEMENTS
C O O CO O
(black solid) (colourless gas,that supportscombustion)
(a colourless gas, that extinguishes fire)
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Copy the Table and fill in the last column.
SiO2Sand
HgMercury
Fe2O3Rust
O2Oxygen
H2OWater
CuSO4Copper sulphate
NiNickel
NaClSodium chloride
Element or compound
FormulaName
compound
element
compound
compound
element
compound
element
compound
Rust consists of
iron combined
with oxygen
Activity
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Bonding and atoms
–Protons } These exist in –Neutrons } the nucleus.
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:
–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
BUTBUT atoms have equal numbers of protons and electrons. This means their overall charge = zero.
FluorineFluorine
9 protons 9+
9 electrons 9-
10 neutrons 0
Total Charge 0
19
F9
For example 20
Ne10
Neon Copy & Fill in the gapsNeon Copy & Fill in the gaps
___ protons ___
___ electrons ___
___neutrons ___
Total Charge ___
10
10
10
10+
10-
0
0
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Noble Gases: full shells
The electrons around the outside of atoms are arranged in layers called shells
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.
1st Shell: 2 electrons
2nd Shell: 8 electrons
3rd Shell: 8 electrons
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Types of bonding
Atoms can be joined together in 3 possible ways
All three types involve changes in the electrons in the outermost electron shells of the atoms
Ionic Bonding
Metal and non-metal
Covalent Bonding
Non-metals only
Metallic Bonding
Metals only
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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
IONIC BONDING
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opposites
attract
Opposites attract – lattices
The oppositely charged ions are attracted into a lattice that gets bigger and bigger until it consists of millions of ions
+
++
+
+
+
-
--
-
--
+ -+ -+-
+ -+-
+
-+ -
+-+
--+ +
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 3-D 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 chloride1. Formation of sodium ions
Sodium has 1 electron in its outer shell.
If it loses this it will have no partially filled shells.
Loses 1 electron
Sodium 1+ ion (2.8.0)Sodium atom (2.8.1)
This only happens if there is another atom able to accommodate the lost electron.
Na Na+
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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.
Chlorine atom (2.8.7)
Gains 1 electron(from sodium)
Chlorine I - ion (2.8.8)
Cl Cl
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Formation of Sodium Chloride- the overall process.
ClNa
Na Cl
Sodium loses itsouter electron.Chlorine gains it.The result is both end up with full shells
Two oppositelycharged ionsare formed, which attract.Millions of such pairs form a giant lattice
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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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OMg
2.8.2. 2.6
Magnesium atom
Oxygen atom
Bonding in Magnesium Oxide
More than one electron may be transferred between atoms in ionic bonding.
Mg2+ O2-
2.82.8
Magnesium Oxide
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Draw a simplified bonding diagram (omitting inner shells) for magnesium oxide.
MgO
Magnesium atom
Oxygen atom
Mg2+ O2-
Magnesium Oxide
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Sodium Fluoride
Sodium atom Fluorineatom
Copy the diagram and draw another box showing the electron configuration in sodium fluoride.
Na+
2.82.8
FNa
2.8.1. 2.7
F-
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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
Li
OLi+
Li+
O2-
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Bonding in Lithium Nitride
The bonding in lithium nitride similarly involves different numbers of each atom.
N
Li
Li
Li
Li+
Li+
N3-
Li
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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
Al Al
F
F
F
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Following the previously shown slides draw bonding diagrams for the compounds formed from the following atoms:
1. Lithium (2.1) and fluorine (2.7)2. Sodium (2.8.1) and sulphur (2.8.6)3. Magnesium (2.8.2) and sulphur (2.8.6)4. Magnesium (2.8.2) and fluorine (2.7)5. 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
Activity
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2 electrons
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 Cl1 electron Na+ Cl-
OMg O2-Mg2+
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.
The formula will be Na2O.
NaO
Na
Na+
O2-
Na+
1 electron per sodium
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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.
The formula will be MgCl2
ClMg
Cl
Mg2+
Cl-
Cl-
2 electrons
Different numbers of electrons
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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,
Mg
2.8.2 Mg2+
Al
2.8.3 Al3+
Li
2.1Li+
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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-
ClO
2.62.8 O
O2-
2.8.7 2.8.8 Cl Cl-
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Copy out and fill in the Table below showing what charge ions will be formed from the elements listed.
H He
Li
Na
K
Be
Sc Ti
Mg
V Cr Mn Fe Co Ni Cu Zn Ga Ge Se BrCa Kr
Al P
N O
S Cl
F Ne
ArSi
B C
As
Mg
C
Cl
K
Na
Charge
Outer electrons
NeBrOAlKCaClNLiSymbol
1 5 7 2 1 3 6 7 1 8
1+ 3- 1- 2+ 1+ 3+ 2- 1- 1+ 0
Activity
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The formulae of ionic compounds
This is most quickly done in 5 stages.Remember the total + and – charges must =zeroRemember the total + and – charges must =zeroFor example, For example, the formula of calcium bromide.
1. Symbols: Ca Br2. Charge on ions 2+ 1-3. Need more of Br4. Ratio of ions 1 25. Formula CaBrCaBr22
BrCa
Br
Ca2+
Br-
Br-
2 electrons
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For example, the formula of aluminium bromide.
1. Symbols: Al Br2. Charge on ions 3+ 1-3. Need more of Br4. Ratio of ions 1 35. Formula AlBrAlBr33
BrAl
Br
Br
3 electrons
Al3+ Br-
Br-
Br-
The formulae of ionic compounds
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For example, the formula of aluminium oxide.
1. Symbols: Al O2. Charge on ions 3+ 2-3. Need more of O4. Ratio of ions 2 3 (to give 6 e-)5. Formula AlAl22OO33
OAl
O
OAl
2e-
2e-
2e-
Al3+
O2-
O2-
O2-
Al3+
The formulae of ionic compounds
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Using the method shown on the last few slides, work out the formula of allall 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
Activity
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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.
Atoms presentChargeFormulaIon
2-
1-
1+
2-
1-
CO32-
OH-
NH4+
SO42-
NO3-
carbonate
hydroxide
ammonium
sulphate
nitrate N O O O
OS OOO
N H H H H
O H
C O O O
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1. Symbols: Li NO3-
2. Charge on ions 1+ 1-
3. Need more of neither
4. Ratio of ions 1 1
5. Formula LiNOLiNO33
• 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?
More Complicated Formulae
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1. Symbols: Mg NO3-
2. Charge on ions 2+ 1-
3. Need more of NO3-
4. Ratio of ions 1 2
5. Formula Mg(NOMg(NO33)2
• What is the formula of magnesium nitrate?
• 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.
More Complicated Formulae
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• What is the formula of sodium sulphate?
1. Symbols: Na+ SO42-
2. Charge on ions 1+ 2-
3. Need more of Na+
4. Ratio of ions 2 1
5. Formula NaNa22SOSO44
• No brackets here as only one SO42- ion needed.
• Note although Na contains 2 letters it only represents a single atom – so no brackets!
More Complicated Formulae
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1. Symbols:
2. Charge on ions
3. Need more of
4. Ratio of ions
5. Formula
Again we need brackets as 3 complete OH- ions are needed meaning that for each aluminium there are 3 oxygens and 3 hydrogens.
Al3+ OH-
3+ 1-
OH-
1 3
Al(OH)Al(OH)33
Write down how to work out the formula of aluminium hydroxide.
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1. Symbols:
2. Charge on ions
3. Need more of
4. Ratio of ions
5. Formula
Again we need brackets as 2 complete NH4+ ions are needed meaning
that for each sulphate ion there are 2 nitrogen and 8 hydrogens.
NH4+ SO4
2-
1+ 2-
2 1
(NH(NH44))22SOSO44
NH4+
Write down how to work out the formula of ammonium sulphate.
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1. Symbols:
2. Charge on ions
3. Need more of
4. Ratio of ions
5. Formula
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.
Al3+ SO42-
3+ 2-
2 3
AlAl22(SO(SO44))33
Need to get total charge =6
Write down how to work out the formula of aluminium sulphate.
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• Formed when a _____ and non-metal react.• Metals ___ electrons to empty their outer
electron shell.• Non-metals _____ electrons to fill their outer
electron shell.• The ratio of metal ions to non-metal ions will
depend upon the number of ________ lost and gained.
• The ions formed join up into giant _____.
Copy this choosing words from below to fill the gaps.
lose lattices
electrons gain metal
metal
lose
gain
electrons
lattices.
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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 NOTNOT true of ionic bonding?
A. Metal ions have a + charge
B. Non-metal ions have a - charge
C. They form a 2 dimensional lattice
D. They have giant structures
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Which of the following is true about the oxide ion?
A. Formed by oxygen atoms losing 2 electrons.
B. Oxygen ions have an empty second shell
C. Exist in pairs
D. Have a 2- charge16
O8
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Which of the following is true about the sodium ion?
A. Has a 2,8,1 electron arrangement
B. Formed by sodium atoms gaining 1 electron.
C. Sodium ions have an empty second shell
D. Have a 1+ charge23
Na11
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What formula compound will be formed from Mn4+ and O2- ions?
A. Mn2O4
B. MnO2
C. Mn2O
D. MnO4