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Chemical 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 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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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
2 possible ways
Metal and
non-metal
Ionic Bonding
Non-metals
only
Covalent Bonding
All three types involve changes in the electrons in
the outermost electron shells of the atoms
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Ionic Bonding
Involves the gain or loss of electrons to
form charged atoms called ions.
The positive ions and negative ions are
attracted to each other and bond together.
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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 (negative)
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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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.
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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 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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• Octet Rule: atoms will bond with other atoms
to gain, lose or share electrons in order to
achieve a full outer shell (i.e. 8)
• Ion = charged atom
• Ionic bond: is formed between positive ions
and negative ions which are attracted to each
other and bond together.
• Most ionic compounds contain a metal and
a non-metal.
• Need to know MgO and NaCl
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COVALENT
BONDING
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Covalent Bonding
Involves the sharing of electrons
between atoms to form molecules
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Covalent compounds
• Covalent compounds are
generally formed when nonmetal atoms react together.
• Sharing of
electrons
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Covalent bonds
•
•
•
Figure 1
Covalent compounds are held together by
this sharing of electrons.
A covalent bond is when a pair of
electrons are shared
It is sometimes represented in full bonding
diagrams (see figure 1). Often these bonds
are just shown as a pair of electrons (xx)
or even just a line (see figure 2).
Figure 2
F XX F
-
F F
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Small covalent structures
• Sometimes just a few atoms join
together in this way.
• .
covalent bonds
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Covalent bonding and electron structures
H
Cl
Cl
H
C
H
H
H
N
H
Cl
H
H
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Covalent bonding in chlorine
Chlorine (2.8.7) needs 1 more electron to
attain a full electron shell.
Cl
Cl
(2,8,7)
(2,8,7)
Cl-Cl
Cl
(2,8,8)
Cl
(2,8,8)
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Both fluorine and chlorine needs 1 more
electron to attain a full electron shell.
F
(2,7)
Cl
Copy this diagram and
add the electron
arrangements that
could exist in fluorine
chloride (FCl).
(2,8,7)
F
(2,8)
Cl
(2,8,8)
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Covalent bonding in hydrogen chloride
Both hydrogen (1) and chlorine (2.8.7) needs 1 more
electron to attain a full outer shell.
H
Cl
(1)
(2,8,7)
H-Cl
H
Cl
(2)
(2,8,8)
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Covalent bonding in water
Hydrogen (1) needs 1 more electron but oxygen (2.6)
needs 2 more. Therefore, we need 2 hydrogens.
H
O
H
O
H
H
O
H
H
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•
Hydrogen (1) needs 1 more electron.
•
How many does nitrogen (2.5) need?
3
•
How many hydrogens per 1 nitrogen?
3
•
Draw bonding diagrams for ammonia.
H
N
H
H
H
N
H
H
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•
Hydrogen (1) needs 1 more electron.
•
How many does carbon (2.4) need?
4
•
How many hydrogens per 1 carbon?
4
•
Draw bonding diagrams for methane.
H
H
H
C
H
H
H
C
H
H
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Covalent bonding in oxygen
Oxygen (2.8.6) needs 2 more electrons to attain a
full electron shell.
O
O
4 electrons
O
O=O
O
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Nitrogen (2.8.5) needs 3 more electrons to attain a
full electron shell and forms a triple bond.
Draw a bonding diagram of nitrogen.
6 electrons
N
N=N
N
N
N
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Draw ‘dot and cross’ type bonding diagrams for
Bohr Models
each of the following:
1. Hydrogen fluoride (HF)
2. Hydrogen sulphide (H2S)
3. Ethane (C2H6 and the carbons are joined by a
single covalent bond)
4. Carbon dioxide (CO2 and the carbon oxygen
bonds are double bonds)
H
F
H
H
S
H
H
H
C
C
H
H
H
O
C
O
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Giant covalent structures: diamond
• One form of carbon
is diamond.
Diamond
strong
covalent
bonds
• Each diamond
consists of millions
of carbon atoms
bonded into a single
giant structure.
• It is very hard.
carbon atoms
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BONDING AND PHYSICAL
PROPERTIES
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Bonding and physical properties
The type of structure that substances have has a
huge effect upon physical properties.
These are things such as:
•
•
•
•
Density
Conductivity
Malleability/ brittleness
Melting point
The next few slides illustrate just a few of the general patterns.
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