2. WHAT'S AN ATOM?
DEFINITION:
A MICROSCOPIC SMALL PARTICLE THAT COULD
NOT BE MADE ANY SMALLER AND STILL BEHAVE AS
A CHEMICAL SYSTEM.ATOMS ARE THE SMALLEST
PARTICLES THAT CAN EXIST AND REPRESENT
ELEMENTS IDENTITY.ATOMS CANNOT BE CREATED
OR DESTROYED
3. ATOMS
• Atoms consist of protons, neutrons,
electrons
• The atomic structure is shown in the
diagram below
• Protons have positive charge
• Electrons have negative charge
• Neutrons have no charge
4. ATOMIC STRUCTURE
Properties
Particle Mass (kg) Mass (amu)#
Charge*
Electron 9.10939 x 10 -31
0.00055 = 0 - 1
Proton 1.67262 x 10 -27
1.00728 = 1 +1
Neutron 1.67493 x 10 -27
1.00866 = 1 0
5. ATOMIC PARTICLES:
• Atoms consist of three subatomic particles:
• electrons
• electrons are negatively charged particles
and their properties are summarized in
the following table
• protons
6. ATOMIC PARTICLES:
• protons are positively charged particles
and their properties are summarized in
the following table
• neutrons
• neutrons have no charge and their
properties are summarized in the
following table
7. ELECTRONS
• Small negatively charged particle
• Orbit, circle, around the nucleus
• Have no mass.
• Atoms are neutral.
• Number of electrons = number of
protons
8. PROTONS:
• small, positively charged particles
• reside in the nucleus
• along with the neutron, make up most of the
mass of the atom
• the number of protons is what defines the type
of a particular atom.
• Atoms are neutral
• Number of protons = number of electrons
9. NEUTRONS:
• small particles with no charge
• reside in the nucleus
• along with the proton, make up most of
the mass of the atom
• a differing number of neutrons is what
defines an "isotope" of an atom
10. WHAT'S A MOLECULE?
Definition:
The smallest particles of an element or
compound that can exist and retain the
chemical properties of that element or
compound
12. ATOMIC AND MOLECULAR
STRUCTURE
ALL MATTER LIVING OR DEAD CONSISTS OF
MATERIALS. IN NATURE THEIR ARE 116
FUNDAMENTAL MATERIALS THESE ARE CALLED
ELEMENTS.
DEFINITION:AN ELEMENT IS A SUBSTANCE THAT
CANNOT BE SPLIT UP INTO TWO OR MORE
SUBSTANCES BY CHEMICAL MEANS.
ELEMENTS MAY BE:A. SOLID-IRON, CARBON
B. LIQUIDS- MERCURY, BROMINE
C. GASES- OXYGEN, HYDROGEN
THE ELEMENTS ARE ALL COMPOSED OF PARTICLES
SMALLER THAN ATOMS KNOWN AS ELECTRONS,
PROTONS AND NEUTRONS
13. COMPOUNDS
ONLY FEW ELEMENTS ARE FOUND FREE IN NATURE: E.G.
CARBON, NITROGEN , OXYGEN, SULPHUR,THE NOBLE GASES,
COPPER AND GOLD.
MOST ELEMENTS ARE FOUND AS COMPOUNDS. COMPOUNDS
ARE FORMED BYTWO OR MORE ELEMENTS COMBINING
TOGETHER MILLIONS OF COMPOUNDS ARE KNOWN AND
CARBON ISTHE ELEMENT THAT FORMS THE MOST.
DEFINITION:A COMPOUND IS A SUBSTANCE WHICH
CONTAINS TWO OR MORE ELEMENTS COMBINED IN SUCH A
WAY THEIR PROPERTIES ARE CHANGER
MOLECULES:ATOMS OF AN ELEMENT MAY NOT BE ABLE TO
EXIST SINGLY:THE ATOMICITY OF AN ELEMENT IS THE NUMBER
IF THE ATOMS IN ON MOLECULE
DEFINITION:THE MOLECULE IS THE SMALLEST PARTICLE OF AN
ELEMENT WHICH CAN EXIST IN THE FREE STATE UNDER
ORDINARY CONDITIONS.
14. COMPOUNDS
• compounds are composed of two or more atoms
chemically combined in fixed proportions
• for example, water, H2O, always occurs in a
ratio of 2 hydrogens : 1 oxygen—
• if the ratio were anything else it would not be
water, H2O2 with a ratio of 2 : 2 is peroxide,
certainly not water
15. MIXTURES
A pure substance is one in which all the molecule alike.
Element and compounds are the only pure substances
that can exist. If two or more kinds of molecules are
present together they form a mixture. Most of the
materials encountered are mixtures: air, earth, sea water,
plants. One of the chemicals most important and
difficulty jobs is to sort out the naturally occurring
mixtures into their pure components in order to
characterize them.
Definition: a mixture contains two or more different
substances either elements or compounds, which are
not chemically joined together
16. MIXTURES AND COMPOUNDS
Mixtures and compounds both contain more than one
element and so should be separable into their component
elements.This process may be easy or difficult but it is not
the only criterion for deciding whether a given material is
a mixture or a compound.
Example: consider two elements iron and sulphur
Iron – form of fillings
Sulphur- form of yellow powder
Mix them together without heat mixture
Heat mixture in a test tube
This process of water of crystallization in a substance e.g.
copper sulphate -5- water does not make it a mixture
because the composition is fixed.
