Download Bonding and Properties of Compounds

Higher Chemistry
Bonding and Properties
NEW LEARNING
REVISION
Elements are the simplest
substances and consist of
one type of atom.
They are arranged in the
Periodic table in increasing
atomic number.
Grouping elements by bonding
and structure – focus on
Titanium
Grouping compounds and
elements by bonding structure
and properties.
Periodic trends
Lesson 1: Bonding and Properties
Today we will learn to
Explain the properties of substances
based on their bonding type.
We will do this by
Investigating melting point and solubility
for a variety of substances, including
those involved in extracting titanium.
We will have succeeded if
We can correctly identify bonding type
from properties..
Bonding and Properties
Melting & Boiling Points When metals melt, metallic bonds are broken. In
the case of ionic lattices it is the ionic bonds that are broken. In covalent
networks it is the covalent bonds that are broken. However in covalent
molecules it is the Van der Waal forces that are broken. The stronger the
bond or force that needs to be broken to get the substance to melt or
boil, the higher its melting or boiling point.
Viscosity
The stronger the force of attraction between molecules
the greater the viscosity or thickness of a liquid.
Electrical Conductivity In order for something to be able to conduct it
must contain charged particles (electrons or ions) that are free to move.
Solubility
As a rule of thumb, in terms of solubility, “like dissolves
like”. In other words ionic and polar molecules tend to dissolve in polar
solvents and non-polar molecules tend to dissolve in non-polar solvents.
Metals and covalent networks are insoluble but metals can sometimes react
to form soluble products.
Bonding, Solubility and Solutions
•
Ionic lattices and polar covalent molecular compounds tend to
be:
Soluble in water and other polar solvents, due to the attraction
between the opposite charges.
 Insoluble in non-polar solvents, as there is no attraction between
the ions and the solvent molecules.
e.g. when ionic compounds dissolve in water the lattice is broken up and
the ions are surrounded by water molecules.

Water
molecule
+
+
+
-
+
+
+
+
-
+
+
-
+
Ionic
lattice
+
-
-
+
-
+
+
+ve ions attracted to –ve
ends of water molecule
Hydrated
ions
+
+
-
-
+ +
+
+
-
-ve ions attracted to +ve
ends of water molecule
•
Non-polar covalent molecular substances tend to be:


Soluble in non-polar solvents like carbon tetrachloride or hexane.
Insoluble in water and other polar solvents as there are no
charged ends to be attracted.
‘Like dissolves like’
Bonding and Solubility
Solvent
Substance
Salt (NaCl)
Sugar (C12H 22O11)
Wax (C60H122)
Sand (SiO2)
Bonding Type
Water
(Very Polar)
Ethanol
(Polar)
Pentane
(Non-Polar)
Bonding and Properties of Compounds
•
Compounds can be split into 3 main groups, depending
on their bonding, structure and properties:
1. Ionic Lattice Structures
2. Covalent Network Structures
3. Covalent Molecular Structures
1. Ionic Lattice Structures
•
•
All ionic compounds are solids at room temp so have high
melting and boiling points.
This is because the ionic bonds holding the lattice
together are strong and a lot of energy is required to
break them.
(image from bbc.co.uk)
•
The size of the ions will effect the strength of the
ionic bond and how the ions pack together.
E.g. NaF - m.p 1000oC, NaI - 660oC.
•
Ionic compounds conduct electricity when dissolved in
water or when molten as the ions are free to move.
Electrolysis of an ionic solution or melt causes a chemical
change at the electrodes.
They do not conduct when solid as the ions are ‘locked in
the lattice and cannot move to carry the current.
•
•
2. Covalent Network Structures
•
•
Covalent networks have very high melting and boiling points as
many strong covalent bonds need to be broken in order to
change state.
They can also be very hard.
E.g. Silicon Carbide (SiC) – carborundum, similar structure to
diamond
Tetrahedral
shape
Covalent
Bond
The 4 carbon atoms are available
to bond with another 4 silicon
atoms resulting in a covalent
network.
= Carbon
= Silicon
•
•
It has a high melting point (2700oC)
SiC is used as an abrasive.
•
Covalent network structures are usually non-conductors
of electricity as they have no free moving charged
particles.
3. Covalent Molecular Structures
•
Usually have low melting and boiling points as there is
little attraction between their molecules.
E.g. Carbon dioxide CO2: m.pt -57oC
•
Compounds with polar molecules may have slightly higher
m.pts and b.pts than non-polar molecules due to
permanent dipole-permanent dipole attractions.
e.g. Iodine chloride
Bromine
I - Cl
b.pt 97oC
•
(non-polar)
Br – Br
b.pt 59oC
When hydrogen bonds are present, the compounds will
have a much higher m.pt and b.pt than other compounds
of similar molecular size as more energy is required to
separate the molecules.
(see earlier note on hydrogen bonding – ethanol and ether)
Bonding and Properties
Extracting titanium from its ore, rutile, involves a number of
reactions and processes. Understanding the bonding types and
the effect of the properties of substances was very important in
working out this method.
Property
Bonding Type
Metallic
(titanium)
Ionic
(titanium dioxide)
Covalent Network
(silicon dioxide)
Covalent Molecule
(titanium chloride)
Melting Point
Electrical Conductivity
Solvent most likely to
be soluble in
Starter Task
Complete Quick Test 5 in your booklet
and we will review as a class. You have
10minutes!
Answers
Quick Test 5
1.
2.
3.
4.
5.
6.
A
D
C
B
D
C
Lesson 2: Identifying Unknowns
Today we will learn to
Identify the bonding in unkown substances.
We will do this by
Investigating melting point and solubility for
a variety of substances, and matching
properties to the chemicals given.
We will have succeeded if
We can correctly identify bonding type from
properties..
Identifying Unknowns
Activity 1.15
Identifying Unknown Substances Challenge
You will be given 15 substances labelled from A to O. Using the
information given on the accompanying sheet and the results of
any experiments you use to test the properties of the substances;
you need to identify each substance, their bonding type and give a
reason for your choice.
In the first instance it is helpful to write down what you know
about them what their likely properties will be.
Identifying Unknowns
copper chloride,
silicon oxide (sand),
sugar (C12H22O11),
copper carbonate,
oxygen,
sodium chloride,
iron,
alcohol (C2H5OH),
nickel chloride,
polyethene ([-CH2-CH2-]n),
sulfur,
hydrogen,
pentane (C5H12),
calcium carbonate (chalk)
copper.
What can you easily test?
Identifying Unknowns
Substance
Melting
point
(0 C)
A
>1000
B
> -140
C
>1000
D
>300
E
>100
F
>300
G
> -140
H
>1000
I
>300
J
>100
K
>300
L
>100
M
<-200
N
>1000
O
<-200
Name
Bonding type
Reason