KS4 Covalent Bonding
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Transcript of KS4 Covalent Bonding
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KS4 Chemistry
Covalent Bonding
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Covalent Bonding
Covalent bonding in elements
Covalent bonding in compounds
Summary activities
Covalent structures
Contents
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The covalent bond
When non-metal atoms react together, they need to gain
electrons to fill their outer shell and become stable.
They can only do this if they share electrons with each other.
The atoms share electrons so there is a strong force that
joins the atoms together. This is called a covalent bond.
HHincomplete
outer shells
HH
both atoms have a
full outer shell
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Covalent bonding and elements
Many elements exist as molecules two or more atoms
joined by a covalent bond. Each atom has a full outer
electron shell and is therefore stable.
Two common ways to indicate a covalent bond are:
Only the outer shell of electrons is involved in covalent
bonding. This means that the inner shells do not always
have to be included in diagrams.
H H Cl
dot and cross
diagramHHsolid line
H H
H H
O O Cl
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Covalent bonding in hydrogen
Hydrogen (electron configuration: 1) needs 1 more electron
to have a completely full outer shell.
H2 or HH
HH
There are two atoms in the molecule so it is called diatomic.
To achieve this, it can share an electron with another
hydrogen atom. This creates a single bond and the two
hydrogen atoms form a hydrogen molecule.
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Covalent bonding in chlorine
Chlorine (2.8.7) needs 1 more electron to have a completely
full outer shell.
Cl
Cl
Cl2 or ClCl
To achieve this, it can share an electron with another chlorine
atom. This creates a single bond.
Cl
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O
Covalent bonding in oxygen
Oxygen (2.8.6) needs 2 more electrons to have a completely
full outer shell.
O2 or O=O
To achieve this, it can share two electrons with another
oxygen atom. This creates a double bond.
O OO
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Covalent bonding in nitrogen
Nitrogen (2.8.5) needs 3 more electrons to have a completely
full outer shell.
N2 or NN
It can share three electrons with another nitrogen atom to do
this. This creates a triple bond.
NN NN
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Covalent Bonding
Covalent bonding in elements
Covalent bonding in compounds
Summary activities
Covalent structures
Contents
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Covalent bonding in compounds
Covalent bonding can take place between atoms of different
elements to create molecules ofcovalent compounds.
These covalent bonds can be single, double or triple.
Both hydrogen (1) and chlorine (2.8.7) need 1 more electron
to fill their outer shell. By sharing one electron each, they can
fill their outer shells and become stable.
HCl or H Cl
ClH
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O
Covalent bonding in water
Oxygen (2.6) needs 2 more electrons, but hydrogen (1) only
needs 1 more. How can these two elements be covalently
bonded?
The oxygen atom shares 1 electron with 1 hydrogen atom,
and a second electron with another hydrogen atom.
H2O or H O H
H H
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N
N H
Electron
configuration
Electronsneeded
Ratio of
atoms
Covalent bonding in ammonia
How are nitrogen and hydrogen bonded in ammonia?
2.5 1
3 1
1 3
H
H
NH3 or H N H
H
H
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C H
Electron
configuration
Electronsneeded
Ratio of
atoms
Covalent bonding in methane
How are carbon and hydrogen
bonded in methane?
2.4 1
4 1
1 4
CH4 or H C H
H
H
CH
H
H
H
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More covalent bonding diagrams
Draw a line diagram to show the bonding in:
1. hydrogen sulfide
3. ethane (C2H6)
2. carbon dioxideOO C
HH SS
H H
H
H
C HC
H
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Covalent bonding
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Covalent Bonding
Covalent bonding in elements
Covalent bonding in compounds
Summary activities
Covalent structures
Contents
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Simple covalent structures
Atoms that join together by covalent bonding can form
different types of covalent structure.
Oxygen, water and carbon dioxide are molecules. They have
a simple structure because they only contain a few atoms.
OO COOH
OH
Most molecular substances are gas or liquid at roomtemperature. A few are solid and these are called
molecular solids.
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Molecular solids iodine
Iodine is a molecular solid at room temperature.
Millions of iodine molecules
are held together by weak
forces of attraction to create
a 3D molecular lattice.
Two iodine atoms form a single covalent
bond to become an iodine molecule.
I
I
weak forces
of attraction
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Properties of molecular solids
are usually insoluble in water but soluble in other solvents
such as petrol;
cannot conduct electricity there are no free electrons to
carry an electrical charge.
In addition, molecular solids:
have low melting and boiling points;
are usually soft and brittle they shatter when hit.
The weak forces of attraction between molecules in molecular
solids only require a small amount of energy to be broken.
This means that molecular solids:
G
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Giant covalent structures
In some substances, millions of atoms join together by
covalent bonding. This produces giant covalentstructures,
not molecules.
All the bonds are covalent,
which means that giant
covalent structures have a veryhigh melting and boiling point.
This also means that
almost all giant covalentstructure are hard but
brittle.
All t f b
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Allotropes of carbon
In the element carbon, atoms bond in different ways, creating
different kinds of giant structures.
Two of these structures are diamond and graphite. They
are called allotropes of carbon.
Allotropes have the same chemical properties because they
have the same number of electrons.However, they have different physical properties because the
electrons are shared in different ways with other atoms.
Th t t f di d
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The structure of diamond
Diamond is a rare form of
carbon in which each atom
is covalently bonded to fourothers.
This pattern arrangement is
repeated millions of times to
create a giant lattice.
C
C
C
C
C
Th ti f di d
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The properties of diamond
All the electrons in the outer shell of the carbon atom (2.4) are
used in covalent bonds. This affects diamonds properties.
Diamond is very hard the
hardest natural substance on Earth.
Diamond has a very high melting
and boiling point a lot of energy is
needed to break the covalent bonds.
Diamond cannot conduct
electricity there are no free
electrons or ions to carry a
charge.
Th t t f hit
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The structure of graphite
Graphite is a much more
common form of carbon. in
which each atom iscovalently bonded to three
others.
This forms rings of six atoms,
creating a giant structure
containing many layers. Theselayers are held together by
weak forces of attraction.
C
C C
C
weak forces of attraction
Th ti f hit
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The properties of graphite
Only three of the four electrons in the outer shell of the
carbon atom (2.4) are used in covalent bonds. This affects
graphites properties.
Graphite is soft and slippery
layers can easily slide over each
other because the weak forces of
attraction are easily broken. This iswhy graphite is used as a lubricant.
Graphite can conduct
electricity the onlynon-metal to do. There is a
free electron from each atom
to carry a charge.
All t d th i ti
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Allotropes and their properties
How do the different properties of diamond and graphite
depend on their structures?
Oth ll t f b
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Other allotropes of carbon
Other allotropes of carbon have been discovered in the last
30 years. They are large but not really giant structures.
One allotrope is buckminsterfullerene. It contains 60 carbon
atoms, each of which bonds with three others by forming two
single bonds and one double bond.
These atoms are arranged in 12 pentagons and 20 hexagonsto form spheres, which are sometimes called bucky balls.
C
C C
C
Sand
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Sand
Sand is an impure form of silicon dioxide (quartz). It has a
giant covalent structure with certain similarities to diamond.
Si
O
O
O
O
Each silicon atom (2.8.4) is bonded to four
oxygen atoms, and each oxygen atom (2.6)
is bonded to two silicon atoms.
Bonding and structure
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Bonding and structure
Contents
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Covalent Bonding
Covalent bonding in elements
Covalent bonding in compounds
Summary activities
Covalent structures
Contents
Glossary (part 1)
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Glossary (part 1)
allotropeA structurally different form of an element withdifferent physical properties.
covalent bondA strong bond between two atoms inwhich each atom shares one or more electrons with theother.
covalent compoundA compound containing atomsjoined by covalent bonds.
double bondA covalent bond in which each atomshares two of its electrons.
giant structure
A structure containing millions of atoms
or ions bonded together. The structure extends in threedimensions until all available atoms are used up.
Glossary (part 2)
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Glossary (part 2)
molecule A simple structure containing two or moreatoms covalently bonded together.
molecular solid A solid substance made up ofmolecules held together by weak forces of attraction, forminga lattice.
single bondA covalent bond in which each atom sharesone of its electrons.
triple bondA covalent bond in which each atom sharesthree of its electrons.
Anagrams
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Anagrams
Multiple choice quiz
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Multiple-choice quiz