CHEMICAL BONDING
3.2
LEARNING OBJECTIVES
 Be able to define bonding and explain the need to bond?
 Describe the different bonding types?
Ionic
Covalent
Polar – Covalent
Metallic
 How to predict bonding preference for elements?
 Relate type of bonding to properties of molecules
 Relate properties of substances to their uses
 Be able to suggest the type of structure of a substance given its
properties
ELECTRONIC CONFIGURATION AND LEWIS
DOT STRUCTURE
Video
 https://www.youtube.com/watch?v=o4J9mLbvWJA
WHAT IS A CHEMICAL BOND ?
Bond is a force of attraction that holds atoms together.
Electrons in atoms are responsible for holding them together.
Bonding is a way to gain stability.
TYPES OF BONDS
There are mainly three
types of bonds:
1. Ionic bond
2. Covalent
bond
3. Metallic
bond
macromolecules
HOW TO PREDICT BONDING PREFERENCE?
You can tell what type of bonding is in a substance by looking at
whether the elements in it are metals or non-metals:
METAL
NON-METAL
METAL
Metallic bond
Ionic bond
NON-METAL
Ionic bond
Covalent bond
STARTER
Sort the compounds below into groups within the circles below according to their
chemical bonding;
Sodium chloride, NaCl
Magnesium, Mg
Methane, CH4
Magnesium oxide, MgO
Aluminium, Al
Caesium, Cs
Covalent
Ionic
Barium iodide, BaI2
Oxygen, O2
Ammonia, NH3
Metallic
STARTER
Complete the starter sheet – Which type of chemical bond.
CH4
NaCl
MgO
O2
BaI2
NH3
Covalent
Ionic
Mg
Cs
Al
Metallic
IONIC BOND
DEFINITION
Ionic bonding is a type of chemical bonding that involves
the electrostatic attraction between oppositely charged ions.
These ions represent atoms that have lost one or more electron (known
as cations) and atoms that have gained one or more electrons (known as
an anions).
In the simplest case, the cation is a metal atom and the anion is a
nonmetal atom
EXAMPLE-IONIC BONDING
TRY AND DRAW DIAGRAMS TO SHOW
HOW THE FOLLOWING COMBINATIONS
WOULD BOND TOGETHER
1.
Lithium and chlorine
2.
Calcium and oxygen
3.
Potassium and bromine
4.
Magnesium and fluorine
5.
Magnesium and oxygen
6.
Beryllium and oxygen
7.
Calcium and chlorine
PROPERTIES OF IONIC COMPOUNDS
1.
Crystalline solids
made of ions
2.
High melting/boiling points
Solids at room temperature and strong electrostatic bonds
3.
Many are soluble in water
Ions separate when dissolved in water
4.
Liquids & Solutions → Good Conductors
Ions are separated – any substance that has separate charges allow
for conduction of electricity
5.
Solids → Poor conductors
No separation of ions
GIANT IONIC COMPOUNDS
Ionic bonding always results in giant ionic structures. These are
closely packed, regular arrangements of ions where there are very
strong forces of attraction between all the ions in all directions.
The strong bonds between all the atoms cause ionic structures to have
high melting and boiling points. They will, however, eventually melt
and when they do, or when they are dissolved, they are able to
conduct electricity. This is because the ions can carry charge and are
free to move.
YOUR TASK
Complete the questions below. Remember to answer in full sentences.
1. Copy and complete:
Ionic compounds have ______________ melting points and boiling points
because of the strong electrostatic forces of ______________ between
___________ charged ions in the giant _____________. Ionic compounds will
____________ electricity when ____________ or in _____________
because the ions are able to _________ freely.
2. Why is seawater a better conductor of electricity than water from a
freshwater lake?
COVALENT BOND
DEFINITION- COVALENT BOND
A covalent bond is a chemical bond that involves the sharing
of electron pairs between atoms.
Atoms can share one, two or three pairs of electrons to form single,
double or triple bonds respectively.
EXAMPLE- COVALENT BOND
NON – POLAR COVALENT BOND
POLAR COVALENT BONDS
SIMPLE COVALENT MOLECULES
•Covalent bonds can result in the formation of simple covalent
molecules.
Hydrogen H2
Water H2O
Methane CH4
Carbon Dioxide CO2
Ammonia NH3
SIMPLE COVALENT MOLECULES
Substance
Melting Point
(˚C)
Boiling Point
(˚C)
0
99.98
Liquid
Carbon Dioxide
-78
-57
Gas
Methane
-164
-182
Gas
Hydrogen
-259.1
-252.8
Gas
Ammonia
-77.73
-33.34
Gas
Water
State at room
temperature
If we look at the data, we can see that the simple covalent molecules here are
all gases or liquids at room temperature. They all have very low melting and
boiling point. So why is this if covalent bonds are so strong?
INTRAMOLECULAR VS. INTERMOLECULAR
Intramolecular
Intermolecular
Intramolecular forces are the
bonds that occur between
atoms.
Intermolecular forces are those
forces between molecules.
Between simple covalent
molecules, these bonds are very
weak.
These bonds are very strong and
require lots of energy to break
them.
SIMPLE COVALENT MOLECULES
Because the intermolecular forces are so weak, the molecules are
easily parted from each other, hence the low boiling and melting
points.
It is these intermolecular forces that are broken when a compound
boils/melts.
The covalent bods themselves do not break.
PROPERTIES OF COVALENT COMPOUNDS
1.
Gases, liquids, or solids
made of molecules, the bonds are comparatively weaker
2.
Lower Melting Points than ionic compounds
Intermolecular Forces aren’t as strong as interionic forces
3.
Cannot conduct electricity as solid, liquid, or when dissolved
molecules will not separate into ions
4.
Will dissolve in liquids with similar molecular polarity but not in
water. e.g. Benzene, chloroform etc.
“Like dissolves like”
YOUR TASK
Complete the questions below. Remember to answer in full sentences.
1. Copy and complete:
Non-metals react to form ________ which are held together by _______
bonds. These hold the atoms together very _________. The forces between
molecules are relatively weak, so these substances have low ______ and
________ points.
2. A compound called sulfur hexafluoride (SF6) is used to stop sparks
forming inside electrical switches designed to control large currents.
Explain why the properties of this compound make it particularly
useful in electrical switches.
3. The melting point of hydrogen chloride is -115C whereas sodium
chloride melts at 801C. Explain why.
TRY AND DRAW DIAGRAMS TO SHOW
HOW THE FOLLOWING COMBINATIONS
WOULD BOND TOGETHER
1.
2.
3.
4.
5.
6.
7.
8.
9.
Cl2
H2O
CH4
NH3
HCl
N2
C2H4
CH3OH
CO2
GIANT COVALENT STRUCTURES
Covalent bonding does not always result in simple molecules.
Atoms that bond covalently can also form giant structures or
macromolecules.
Diamond, graphite and silicon dioxide are examples of giant covalent
structures of atoms.
DIAMOND
Diamond is the hardest naturally occurring material known to man. The
reason for this property can be explained by the bonding within it.
Each carbon atom forms four covalent
bonds with other carbon atoms to make a
very rigid, giant covalent structure.
Diamond has extremely high melting and
boiling points and is used for jewellery
and drill tips.
GRAPHITE
Carbon can also bond slightly differently to form graphite.
In graphite, the carbon atoms arrange themselves to form layers. The
layers can slide over each other easily, making graphite ideal for pencils
and industrial lubricant.
Each carbon is bonded to three others, making flat hexagonal shapes.
This leaves one electron left over which becomes delocalised and can
move between the layers – these electrons allow graphite to conduct
electricity and heat like metals.
SILICON DIOXIDE
Sometimes called Silica. This is what sand is made from. It is one giant
structure of silicon and oxygen. It can be melted down with sodium
carbonate and limestone to make glass.
YOUR TASK
Complete the questions below. Remember to answer in full sentences.
1. Copy and complete:
Giant covalent structures contain many __________ joined by covalent bonds.
They have _________ melting points and ___________ points. Diamond is a
very __________ substance because the ___________ atoms in it are held
strongly to each other. Graphite, however, is ___________ because there are
__________ of atoms which can __________ over each other.
2. Graphite is sometimes used to reduce friction between two surfaces
that are rubbing together. How does it do this?
3. Explain in detail why graphite can conduct electricity but diamond
cannot.
GIANT IONIC COMPOUNDS
Ionic bonding always results in giant ionic structures. These are
closely packed, regular arrangements of ions where there are very
strong forces of attraction between all the ions in all directions.
The strong bonds between all the atoms cause ionic structures to have
high melting and boiling points. They will, however, eventually melt
and when they do, or when they are dissolved, they are able to
conduct electricity. This is because the ions can carry charge and are
free to move.
YOUR TASK
Complete the questions below. Remember to answer in full sentences.
1. Copy and complete:
Ionic compounds have ______________ melting points and boiling points
because of the strong electrostatic forces of ______________ between
___________ charged ions in the giant _____________. Ionic compounds will
____________ electricity when ____________ or in _____________
because the ions are able to _________ freely.
2. Why is seawater a better conductor of electricity than water from a
freshwater lake?
YOUR TASK - COMPARE AND CONTRAST THE PROPERTIES OF
IONIC AND COVALENT COMPOUNDS USING A VENN DIAGRAM.
1.
2.
Ionic
compounds
3.
4.
5.
PROPERTY
Volatility
Solubility
Electrical
Conductivity
Boiling Point
Melting Point
Covalent
compounds
METALLIC BOND
WHY AND HOW ARE METALLIC BONDS
FORMED?
https://www.youtube.com/watch?v=Bi0rUNV8mEw (2:54)
Alloys -http://www.youtube.com/watch?v=9LHDSB1n11k
PROPERTIES OF METALS
Metals are electron donors and form positive ions while bonding.
The metallic bond accounts for many physical characteristics of metals,
such as strength, malleability, ductility, luster, conduction of heat and
electricity.
PROPERTIES OF METALS
Melting and Boiling Points
metals have high melting and boiling points because of the strength
of the metallic bond.
The strength of the metallic bond depends on the
number of electrons in the delocalized 'sea' of electrons.
(More delocalized electrons results in a stronger bond and a higher melting
point.)
packing arrangement of the metal atoms.
(The more closely packed the atoms are the stronger the bond is and the
higher the melting point.)
Malleable and Ductile
Metals are malleable and ductile. The delocalized electrons in the
'sea' of electrons in the metallic bond, enable the metal atoms to roll over each
other when a stress is applied.
Optical Properties
Metals typically have a shiny, metallic lustre. Photons of light do not
penetrate very far into the surface of a metal and are typically reflected, or
bounced off, the metallic surface.
TO RECAPITULATE
METALLIC STRUCTURES
Metals consist of giant structures of atoms arranged in a regular
pattern.
Each metal atom ‘loses’ it’s outer electrons which become free to move
throughout the metal atoms (we say they are delocalised).
These delocalised electrons hold the atoms together in a regular
structure (acting a bit like a glue).
METALLIC STRUCTURES
The free electrons in metals are the reason that most metals can
conduct electricity and conduct heat.
They also allow the atoms to slide over each other, causing metals to
be malleable.
YOUR TASK
Four substances were tested for various properties with the following
results:
Substance
Melting Pt
(C)
Boiling Pt
(C)
Good
electrical
conductor?
A
-218.4
-182.96
No
B
1535
2750
Yes
C
1410
2355
No
D
801
1413
When molten
Identify the type of bonding in each substance, giving reasons for
your answers.
MAKING METALS HARDER
An alloy is a mixture of two or more elements, one of which is a metal.
Alloys usually have different properties that are different to the
metals they contain. This makes them more useful than the pure metals
alone. For example, they may be harder than the pure metal.
Alloys contain atoms of different sizes which distorts the layers,
preventing the layers from sliding over each other.
NANOSCIENCE
The science of structures that are 1-100nm in size (just a few hundred
atoms)
Nanoparticles have different properties to the same ‘bulk’ materials
e.g. silver has no antibacterial properties in bulk, but can be used in
antibacterial plasters etc as nanoparticles as they take on these
special properties.
Nanoparticles have an extremely high surface area to volume ratio
Uses include – new computers, new catalyst, new coatings, sensors,
stronger lighter construction materials, cosmetics, sun creams.
IMPORTANT LINKS
https://www.youtube.com/watch?v=zpaHPXVR8WU
https://www.youtube.com/watch?v=TxHi5FtMYKk
https://www.youtube.com/watch?v=OQ-pcxo-Q5c
https://www.youtube.com/watch?v=X9FbSsO_beg
https://www.youtube.com/watch?v=S08qdOTd0w0
https://www.youtube.com/watch?v=JPH5-fCxX-Q