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Chapter 4

Chapter 4
by

Jim Burnett

on 29 November 2015

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Transcript of Chapter 4

Elements
substance
Compounds
Mixtures
Understand what are elements,
Elements, Compounds and Mixtures
Chapter 4
Objectives
compounds and mixtures
elements, compounds and mixtures
Describe the differences between
Classification
Elements
Compounds
Mixtures
Pure
Cannot
Solid, liquid or gas
Metal, or non-metal
Atoms
Argon
O
2
O
3
Sodium Chloride
CO
2
H O
2
Molecules / Ions
be broken down into two or more simpler substances chemically
Video: 1:17 - 2:22
represented by chemical symbols (eg. Sodium - Na)
substance
Pure
two or more elements chemically combined
in fixed ratio
different properties as the elements that it is made up of
not
Made up of two or more substances
.


chemically combined
homogeneous / heterogeneous
salt + water oil + water
Both are pure substances
One type of atom
Two or more elements
H
Compounds
Both are made up of more than one type of elements
Mixed in fixed proportion
No fixed proportion
Different physical and chemical properties as constituent elements
Same chemical properties as its components
Chemical reaction takes place when formed - energy involved in its formation
No chemical reaction when formed - no energy involved in its formation
Can be separated into elements by chemical reactions eg electrolysis
Can be separated into its components by physical methods eg filtration
involves an energy change
similar chemical properties as its components
Metals
Non-Metals
Usually high melting / boiling points
Usually low melting / boiling point
Good conductors of heat and electricity
Poor conductors of heat and electricity
Malleable and ductile
Brittle and non-ductile
Shiny and lustrous
Dull in appearance
Sonorous
Non-sonorous
Physical differences
Chemical differences
(Will be covered after learning structure of atoms and bonding)
Proton Number
metalloids
(Behave like both metals and non-metals)
Solid at r.t.p (except Hg)
Usually gases / liquids at r.t.p
Molecules
An atom is the simplest substance of an element which can not be further broken down by chemical process.
Mon
atomic
A molecule is made up of two or more atoms chemically combined together.
Di
Tri
atomic
atomic
Eg. Air (oxygen, carbon dioxide, nitrogen, other gases)
Mixture can exist in various ways
two elements
one element, one compund
two compound
Hydrogen & Neon
Carbon Dioxide
& Water
Hydrogen & Ammonia
The ratios of the components are
not fixed.
S
P
E
C
eparation
roperties
nergy Change
omposition
Mixture
The components of a mixture can be separated by
physical
methods, e.g. filtration, distillation or chromatography.
No chemical reaction takes place when a mixture is formed — usually there is
not fixed
physical
little or no energy change
Alloy
An alloy is a mixture of metals with other elements (usually metals but sometimes non-metals such as carbon).
Alloys are widely used because they tend to be stronger than pure metals.
Pure Metal
Alloy
Examples of Alloy
Steel
: iron, carbon
Stainless steel
: iron, chromium, nickel, carbon
Brass
: copper, zinc
Bronze
: copper, tin
Duralumin
: aluminium, copper, magnesium
Solder
: lead, tin

Ions are electrically charged particles (either positive or negative)
Example: NaCl (Na and Cl )
+
-
Chemical Formula of a Compound
The chemical formula states
the types of atoms

the ratio of the different atoms
H O
2
Hydrogen
Oxygen
Number of Hydrogen atoms (two)
Thus, ratio of H:O is 2:1 and this is
fixed
Naming Compound
1.
A compound made up of two elements has a name that ends in -ide
• Sodium chloride — elements sodium and chlorine
2. A compound that contains hydroxide ions , OH– (a negatively charged ion made up of oxygen and hydrogen) is named a hydroxide.
• Potassium hydroxide — potassium ions and hydroxide ions
3. A compound that contains a negatively charged polyatomic ion containing oxygen usually has a name ending in –ate.
Carbon dioxide — elements carbon and oxygen
• Copper(II) sulphate — contains oxygen atoms in the sulphate ion
Cu
SO
SO
4
4
2-
(sulfate ion)
Writing Chemical Formula
1. For many compounds that contain both metallic and non-metallic elements, the symbol of the metallic element is written first.
2. The number of atoms is written as a subscript, to the right of the atom’s symbol.
• Water (H O, not H2O or 2HO or HO)
Calcium oxide (CaO), Magnesium carbonate (MgCO )
3
2
2
3. It is not necessary to write the subscript ‘1’.
Calcium oxide (CaO, not Ca O )
1
1
4. The oxygen atom is usually written at the end of the formula.
Carbon Monoxide (CO, not OC)
Pb(NO )
3
2
How many atoms of each element are there?
Name the compounds.
MgO
CaCO
3
Heat can be used to break down compounds into elements or simpler compounds. Such a chemical reaction is called thermal decomposition.
Mercury(II) Oxide
Oxygen
Compounds
2
Full transcript