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Copy of Copy of Chemical Bonding, Structure and Properties

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Paul Scarbrough

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Transcript of Copy of Copy of Chemical Bonding, Structure and Properties

Chemical Bonding, Structure and Properties
Lesson 3
GCSE Additional Science
Peaks College
Thursday Matt Cannon

Structure and Bonding
Properties of Compounds
a) describe the properties of metals, ionic compounds, simple molecular covalent substances and giant covalent substances
Explanation of Physical Properties
b) use the sea of electrons/lattice of positive ions structural model for metals to explain their physical properties
c) Use their understanding of electronic structure to explain how ions are formed, and draw dot and cross diagrams to show how ionic bonding takes place in simple binary compounds formed from Group 1 or 2 elements and elements from Group 6 or 7.
Giant Ionic
d) use the accepted structural model for giant ionic structures to explain the
physical properties of ionic substances.
Ions and Ionic Bonding
e) use their understanding of electronic structure to explain how covalent bonds are formed, and draw dot and cross diagrams to show the covalent bonding in simple molecules, including examples which contain double bonds.
Covalent Bonds
Intermolecular Bonding
f) use the intermolecular bonding structural model for simple molecular
structures to explain the physical properties of simple molecular substances.
carbon structures
g) describe the structures of diamond, graphite and carbon nanotubes.
properties of diamond and graphite
h) describe and explain the properties of diamond and graphite, in terms of their bonding and structure, and relate their uses to these properties.
Carbon nanotubes
i) relate the properties and uses of carbon nanotubes to their bonding and
structure.
Physical Properties of Copper

1. High Electrical Conductivity
2. High Thermal Conductivity
3. High Melting and Boiling Point
4. Ductile
5. Malleable
6. Corrosion Resistant
7. Antibacterial
8. Tough
9. Non-magnetic
10. Easy to alloy
11.Attractive colour
12. Recyclable
Physical Properties of Salt

1. High Melting Point
2. Solid Sodium Chloride does not conduct
electricity
3. Molten or aqueous (dissolved in water) sodium
chloride does conduct electricity
4.Soluble in water
5. Brittle
Physical Properties of water-simple covalent

1. Low melting and boiling point
2.Liquid at room temperature
3. Poor conductor of electricity
4. Excellent solvent
Physical Properties of diamond
giant covalent

1. Transparent and Crystalline
2. Extremely hard
3. Electrical Insulator
4. Very high melting point
The atoms in metals have lost their outer
electrons to form positive ions
The outer electrons then can move
freely between theses positive ions
REASONS FOR HIGH MELTING POINT

The metal ion and the free "sea" of electrons are attracted to each other
This electrostatic attraction is called a metallic bond
In order to melt a metal this bond has to be broken
This requires a lot of energy to break
REASONS FOR ELECTRICAL CONDUCTIVITY

The electrons are free to move through the lattice
Because of this they can carry charge through a metal
This charge is an electric current
REASONS FOR HIGH THERMAL CONDUCTIVITY

When a metal is heated it's particles start to vibrate
As they vibrate they cause atoms next to them to vibrate
These increased vibrations can move quickly through a metal
These vibrations spread thermal energy
Ions are formed
by either gaining
or losing electrons

Lithium atoms lose an outer electron
This means they have 3 positive protons
and 2 negative electrons,
this gives them an overall cahrge of +1
Flourine atoms gain one electron
This means they have nine protons
and 10 electrons giving them an
overall charge of -1
Sodium and Fluorine can form an ionic bond.
Sodium needs to lose an electron
Fluorine needs to gain an electron
Sodium therefore donates an electron to fluorine
This creates a positive ion and a negative ion
This creates an attraction between
the +ve ion and the -ve ion
This bond is called an ionic bond
Na
+
Cl
-
REASONS FOR HIGH MELTING POINT

Strong attractive electrostatic forces between +ve sodium ions and -ve chloride ions
Requires alot of energy to break the bond
Therefore high melting point
REASONS WHY SOLID IONIC COMPOUNDS DONT CONDUCT ELECTRICITY

Sodium and chloride ions held in fixed positions
This means they can't move through the compound
Therefore they can't create an electric current
REASONS WHY MOLTEN/DISSOLVED IONIC COMPOUNDS DO CONDUCT ELECTRICITY

When molten or dissolved the lattice breaks down
The ions are then free to move
The moving ions create an electrical current
Water, H O, is an example of a covalent molecular compound

Molecules are formed from atoms when they share electrons

2
Hydrogen has one electron in it's outer shell
It needs one more to get a full outer shell
Oxygen has six electrons in it's outer shell
It needs two more to get a full outer shell
Because Oxygen needs two electrons but hydrogen only needs one electron 2 hydrogens are present.
H
H
H
H
H
O
H
H
H
H
H
O
O
O
O
strong covalent bonds
(very difficult to break)
In between molecules very weak bonds
(very easy to break)
REASONS WHY SIMPLE COVALENT MOLECULES HAVE LOW MELTING POINTS

Although the covalent bonds are very strong and require a lot of energy to break. The bonds between molecules are very weak
This is because each molecule is overall neutral
Very little energy is required to separate the molecule and turn it from solid to liquid
Therefore they have low melting points
REASONS WHY SIMPLE COVALENT MOLECULES ARE POOR CONDUCTORS OF ELECTRICITY

The molecules themselves are overall neutral
Therefore no ions or electrons present to make an electric current
Diamond and Graphite- Giant Covalent Structures
h) describe and explain the properties of diamond and graphite, in terms of their bonding and structure, and relate their uses to these properties.
strong covalent bonds
carbon atoms
REASONS FOR HIGH MELTING POINT IN DIAMOND

Each carbon atom in diamond is connected to 4 other carbon atoms by a strong covalent bond
In order to melt diamond all these strong bonds have to be broken
This requires a lot of energy
Therefore very high melting point
REASONS FOR NON CONDUCTION OF ELECTRICITY

All atoms are bonded
There are no free electrons or ions
Therefore there is no electrical current
carbons bonded to 3 other carbons with covalent bonds
In between sheets of graphite are
delocalised electrons that are free to move
around
REASONS GRAPHITE CAN CONDUCT ELECTRICITY

In between the sheets of graphite are delocalised electrons
These delocalised electrons are free to move
They can therefore create an electric current through graphite
REASONS FOR HIGH MELTING POINT OF GRAPHITE

The atoms are still all held together by strong covalent bonds
These bonds require alot of energy to break
Therefore the melting point is still very high
Carbon Nanotubes
(i) relate the properties and uses of carbon nanotubes to their bonding and
structure
When graphite rolls up on itself a carbon nanotube is formed
WHY ARE NANOTUBES STRONG

Covalently bonded hexagonal sheets mean there's a lot of strong bonds
Nanotubes are 5 times stronger than steel
WHY ARE NANOTUBES GOOD CONDUCTORS

Just like graphite nanotubes have free electrons
These free electrons can move
Therefore an electric current can be created
WHAT ARE THEY USED FOR

1. STRENGTH

nanotubes are light and strong so are in much demand in things like; bike components, boat hulls, wind turbines etc.

2. CONDUCTORS

because they are good conductors nanotubes can be used in circuitry and computers
Smart Materials
(j) know that thermochromic pigments, photochromic pigments, polymer gels, shape memory alloys and shape memory polymers are known as smart materials and have properties which change reversibly with a change in their
surroundings.
What are smart material? Why use the word "smart"? Smart materials have properties which change reversibly with a change in their surroundings. Smart pigments, for example, that are used in some paint applications, change their colour
k) know that the below materials change as follows:
a) Thermochromic pigments – change colour with changing temperature
b) Photochromic pigments – change colour with changing light intensity
c) Hydrogels – absorb/expel water and swell/shrink (up to 1000 times their volume) due to changes in pH or temperature
d) Shape memory alloys – regain original shape when heated
e) Shape memory polymers – regain original shape when heated.
Smart Materials
Thermochromic Pigments
These are materials that change their colour at specific temperatures
As temperature changes they rearrange whcih causes a change in colour
Photochromic Pigments
These change colour with light intensity, when the pigment is exposed to ultraviolet light it breaks bonds in the molecule that cause it to change colour
Hydrogels
Hydrogels are polymers that can absorb or expel water due to changes in pH or temperature

They are used in
Artificial muscles
Underground water cut offs
Houses threatened by forist fires (more effective than fire fighting foam)
Shape Memory Alloys/Polymers

When these are heated they regain their original shape
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