MODEL OF MATTER - ATOMS AND MOLECULES
How does an atom compare in size with other objects?
What is atom?
An atom is the smallest particles of an element
How many times the size of a bacterium is an atom?
2. How many times the size of a red blood cell is an atom?
3. How many atoms would it take to form a dust particle?
Decreasing diameter

(in metre)
1.10^(-2)
1.10^(-3)
1.10^(-5)
1.10^(-6)
1.10^(-7)
1.10^(-10)
pencil core
plant cell
red blood cell
bacteria
dust particles
atom
Figure. the average diameter of an atom relative to the average diameters of other objects
Using models to represent atoms
Atoms of different elements
are represented using
different coloured balls
Since stoms vary in size.
a small atom = a small ball
a big atom = a big ball
Each ball reresents an atom
Each stick represents the force
that holds atoms together
Carbon atoms
Hydrogen
Oxygen
Carbon
iron
gold
Using circle
Different atoms --> different colour
Different size of circles --> different size of atoms
H
O
N
C
Na
Cl
Cu
In nature, there are more than 100 differnent elements.
Using circles or models is not the most convenient way to represent atoms of elements.
Using chemical symbols
USING A MODEL TO REPRESENT THE STRUCTURE OF AN ATOM
What particles does an atom consist of?
What makes up the mass of an atom?
How were models of an atom constructed and revised over the year ?
Electrons move around the nucleus in fixed orbits or paths
An atoms consists mostly of empty space
Subatomic particles
Protons and neutrons are densely packed in the nucleus
A model of an atom
protons, neutrons and electrons
Proton and neutron have the same relative mass.
Electron has negligible mass compared to two particles
Electrically neutral
Atom as a solid,
indivisible ball
Negatively
charged electrons
Positively charged
part of an atom
Positively
charged nucleus
Electrons moving
around the nucleus
An atom
consists
mainly of
empty space
John Dalton`s model
J. J . Thomson`s model
Ernest Rutherford`s model
NIels Bohr`s model
Electrons
moving
around
the nucleus
in fixed orbits
PERIODIC TABLE OF THE ELEMENTS
Mass number
Atomic number = proton number
Symbol of element
Electronegativity
Electron
configuration
The molecule
Ozone depletion
Chemically combined
Molecule
Oxygen
Ozone
Two oxygen atoms
Three oxygen atoms
A molecule is made up of two or more atoms chemically combined
Molecule of elements
Molecule of compounds
A fixed number of
one type of atom
chemically combined
Cl
Cl
O
O
N
N
Gas
Gas
O
O
C
N
H
H
H
Cl
H
A fixed number of
different types of atoms
chemically combined
Gas
Liquid
2 elements
C H O
6
12
NH
3
Ammonia
1 nitrogen atom
3 hydrogen atoms
Glucose
6
3 elements
6 carbon atoms
12 hydrogen atoms
6 oxygen atoms
Chemical
formula
The type of atoms and the number of each type of atom in one molecule of substance