Transcript Elements, Compounds, Mixtures

Chapter 2
Elements, Compounds, Mixtures
An Overview
Introducing Little Miss
“Element”
Hi! I am Little Miss “Element”
I am PURE SUBSTANCE
I cannot be broken down into
any simpler substance by means
of a chemical reaction* or
electricity**!
*Chemical process refers to
chemical reaction or heat
**Electricity refers to
electrolysis
Elements
Definition of an element:
An element is a pure substance which
cannot be split up into two or more
simpler substances by chemical
means.
Sugar is not an element as it can be
broken down into carbon and water.
Elements
Note that an element:
• Consists of only one kind of atom,
• Cannot be broken down into a simpler
type of matter by either physical or
chemical means
• Can exist as either atoms (e.g. argon) or
molecules (e.g., nitrogen).
Examples of elements
Elements are made up of tiny particles
Elements can be further classified into two
groups:
Is the smallest particle
of an element and has
the same chemical properties
of the element
Hi, I am from the
“Noble gas” family
and I work alone
Is made up of two or more
atoms that are chemically
bonded together
(note: these atoms are of the
SAME element!!)
We
same
same!!
These are elements!
Atoms of same element
Cu
copper
element
Na
sodium
element
He
Molecules of same element
H
H
Hydrogen
gas element
helium
element
O
O
ozone
O
Atoms
An element is made of tiny particles
called atoms.
The atoms of an element is different
from that of another element.
ElementsAtoms
Consists of
only one kind
of atom
Microscopic view of
the atoms of the
element argon (gas
phase).
What is an atom?
Examples of models of atoms:
H
Hydrogen
atom
Na
Sodium
atom
Cl
Chlorine
atom
Molecules
Very few elements exists as
atoms besides elements such
For example, hydrogen
is H2.
as helium and neon.
Most elements exist as
molecules.
Ozone is O3.
Hydrogen (H2) is a
diatomic molecule.
Molecules consisting of a
few atoms are called
polyatomic molecules.
Ozone (O3) is a
triatomic molecule.
ElementsMolecules
Consists of
only one kind
of atom
Microscopic view of
the molecules of the
element nitrogen (gas
phase).
Examples of molecules
(elements)
O
H
H
O
O
O
S
O
S
S
S
S
S
N
N
S
S
Chemical Symbols of Elements
Chemists use symbols to represent elements.
For example, O represents oxygen while Fe
represents iron.
Element
Symbol
Element
Symbol
Calcium
Ca
Mercury
Hg
Carbon
C
Neon
Ne
Hydrogen
H
Silicon
Si
Iron
Fe
Sodium
Na
Know Chemical Symbols in Table 1 on page 58
Classification of Elements –
Metals and Non-metals
There are two major groups of elements –
metals and non-metals.
Iron is a metal. Oxygen is a non-metal.
Metals and non-metals are grouped separately
on the Periodic Table.
There are some elements called metalloids
which behave like both metals and non-metals.
What is an element?
An element is a substance that cannot be broken down into
two or more simpler substances by any chemical means.
- They are arranged in the Periodic Table, classified as metals
and non-metals.
- They may consist of atoms of same element or molecules of
Non-metals (including
the same element. Metals (excluding hydrogen)
hydrogen)
Summarising
Elements
Non
Metals
Metals
Atoms
Atoms
Molecules
Compounds
Note that a compound:
• can be broken down into a simpler type of
matter (elements) by chemical means (but
not by physical means),
• has properties that are different from its
component elements, and
• always contains the same ratio of its
component atoms.
What is a compound?
A compound is a substance which is made up of two or
more elements chemically combined together.
- Chemical reactions taking place.
Qn: Is this a compound?
It only contains one type
Cu
of element.
Qn: Is this a compound? Qn: Is this a compound?
H
H
It only contains one type
of element.
O
O
It is not chemically
H
combined.
H
O
So, what is a compound then?
H
H
H
O
H
Water
N
H
Ammonia gas
Consists of two or more elements
And
They are chemically combined together!
Compounds
Microscopic view of
the molecules of the
compound water (gas
phase). Oxygen
atoms are red and
hydrogen atoms are
white.
Making compounds from their elements
Example: Making water (picture)
lighted
splint
ELEMENTS
hydrogen
oxygen
(colourless gas) (colourless gas)
COMPOUND
heat, light
and
explosion
water
(colourless liquid)
Example: Making water (models)
mixture of
hydrogen
heat,
and
oxygen
light and
water
explosion
Hydrogen
molecule
Oxygen
molecule
Water
molecule
Making compounds from their elements
Example: Making iron sulphide compound
compound
elements
heat
Iron
+
sulphur
iron sulphide

heat
+
yellow

grey
black
Summarizing
• A compound is made up of two or more
elements chemically joined together
• A compound has a fixed composition
• Every compound has a unique chemical
formula
• A compound has a completely different
properties from its elements
• A chemical reaction (decomposition or
electrolysis) is needed to separate the
elements in the compound
Molecules- Elements or
compounds?
• A molecule consists of two or more atoms
of the same element, or different elements,
that are chemically bound together.
• It can be a molecule of an element S S S
S
N N O O S
• E.g. N2, O2, S8
S SS
• It can be molecule of a compound.
• H2O, CO2, NH3 O
H
O
O
H
N
H
C
H
H
Introducing Little Mr. “Mixture”
Burp!!!! I am messy!
I am formed when two or more substances
joined together physically (without chemical
bonds)
I have the same properties as all the
substances
I am his best
friend!
AIR
Mixtures
Definition of a mixture:
A mixture is not a pure substance as it
contains a mixture of atoms of
molecules which are not chemically
combined together.
Mixtures
• Note that a mixture:
• consists of two or more different elements
and/or compounds NOT chemically combined.
• Can be homogeneous or non-homogeneous
• can be separated into its components by
physical means, and
• often retains many of the properties of its
components.
Mixtures
Microscopic view of
a gaseous mixture
containing two
elements (argon and
nitrogen) and a
compound (water).
Mixtures
• Examples of mixtures include muddy
water and air.
Air is made up of gases such as nitrogen
and oxygen mixed together.
Little Mr “Mixture”
I do not have a fixed composition of
the substances.
A Mixture can be:
• element + element
• element + compound
• compound + compound
(Refer to page 59, Fig 4.7)
He is a “boo-boo!”
He can be separated to its
substances by physical
methods
A mixture of 2 elements
A mixture of two
elements, e.g. neon
(Ne) and hydrogen (H2)
A mixture of 1 element and
1 compound
A mixture of one
element and one
compound, e.g.
hydrogen (H2) and
ammonia (NH3)
A mixture of 2 compounds
A mixture of two
compounds, e.g.
water vapour (H2O)
and carbon dioxide
(CO2)
Difference between mixtures
and compounds.
Compounds
E.g.
Water H2O
Separation Cannot be separated into its
Mixtures
E.g.
Salt solution
Can be easily separated into
constituents by physical
its constituents by physical
methods. Separation can only
methods.
be done by chemical methods
e.g. Salt can be obtained
or by electricity.
from its solution by
e.g. Water can only be
evaporation. Water can be
separated into Hydrogen and
obtained by simple
Oxygen by Electrolysis.
distillation.
Difference between mixtures
and compounds.
Compounds
E.g.
Water H2O
Mixtures
E.g.
Salt solution
Composition The composition is fixed. The Has no fixed
constituents (elements) in the composition. The
compound are combined in
amount of constituents
definite amount.
in a mixture can vary.
e.g. To form one molecule of
water, two atoms of
Hydrogen and one atom of
Oxygen is needed.
e.g. The amount of
salt added into the
water to make salt
solution can vary and
vice versa.
Difference between mixtures
and compounds.
Compounds
E.g.
Water H2O
Mixtures
E.g.
Salt solution
Properties The physical and chemical The mixture does not have its
properties of the compound
is different from the
properties of its
constituents.
own properties. It has the
average physical and chemical
properties of the constituents that
made it up. (Each constituents
still retain its own properties)
e.g. Hydrogen and Oxygen
are gases while water is a e.g. The salt solution still retains
liquid at room temperature its salt taste.
and pressure.
e.g. Salt solution does not have a
e.g. Water has a fixed
fixed melting or boiling point, but
melting and boiling point.
rather over a range of
temperature.
Difference between mixtures
and compounds.
Energy
Change
Compounds
E.g.
Water H2O
Mixtures
E.g.
Salt solution
Energy is usually given out or
occasionally taken in when a
compound is formed.
Normally little or no
energy is given out or
taken in when a
mixture is formed.
Differences between
mixtures and compounds
Laugh what? I
know I am a
little “bushy and
hairy” than
you…
Mr Messy
*giggles
*
HeE
stupid…
Little Miss Compound
Comparison between
mixtures and compounds
Separation
/breakdown
Properties
(chemical /
physical)
Energy
Change
Mixture
Compound
Components can be
separated by physical
methods
Same properties as its
components
Elements in a compound
Cannot be separated by
physical methods
Properties are unique and
different from its elements
No chemical change
takes place when a
mixture in formed
A chemical reaction takes
place when a compound
is formed
Challenge Time
• Is mineral water an element, mixture or
compound?
Challenge Time
• Are YOU an element, mixture or
compound?
EXTRA!
• Human body is made up of 28 elements?
• About 99% our mass is made up of the 6
main elements
– Oxygen
(65%)
– Carbon
(18%)
– Hydrogen
(10%)
– Nitrogen
(3%)
– Calcium
(1.5%)
– Phosphorus (1.5%)
The End……