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Atoms, Molecules, and Ions
Dalton’s Atomic Theory
Based on 4 postulates
o Elements are composed of extremely small particles,
called atoms.
o All atoms of the same element are identical, having
the same size, mass and chemical properties. The
atoms of one element are different from the atoms of
all other elements.
o Compounds are composed of atoms of more than one
element. In any compound, the ratio of numbers of
atoms pf any of the two elements present is either an
integer or a simple fraction.
o A chemical reaction involves only the separation,
combination, or rearrangement of atoms; it does not
result in their creation or destruction.
General Chemistry I CHM 111
Dr Erdal Onurhan
Slide 1
Atoms, Molecules, and Ions
Representation of Dalton’s Atomic Theory
Note that atoms of element X combine with atoms of element Y in a 2:1 ratio
here. Atoms are neither created nor destroyed in the process
General Chemistry I CHM 111
Dr Erdal Onurhan
Slide 2
Atoms, Molecules, and Ions
Laws of Chemistry
•
•
•
Law of Conservation of Mass – Matter can neither be created nor
destroyed – expressed by Lomonosov in 1748 and placed on experimental
footing by Lavoisier in 1774 – Dalton’s 4th hypothesis is in conformity
with this law
Law of Definite Proportions – different samples of the same
compound always contain its constituent elements in the same
proportion by mass – expressed by Proust in 1799 – Dalton’s 3rd
hypothesis is in conformity with this law
Law of Multiple Proportions – if two elements can combine to form
more than one compound, the masses of one element that combine
with a fixed mass of the other element are in ratios of small whole
numbers – arrived at by Dalton through the 3rd hypothesis.
Another one will be studied later.
General Chemistry I CHM 111
Dr Erdal Onurhan
Slide 3
Atoms, Molecules, and Ions
Cathode-Ray Tube
The cathode ray tube has an
electric field perpendicular to
the direction of the cathode rays
and an external magnetic field.
The symbols N and S denote
the north and south poles of the
magnet. The cathode rays will
strike the end of the tube at A in
the presence of a magnetic
field, at C in the presence of an
electric field, and at B when
there are no external fields
present or when the effects of
the electric field and magnetic
field cancel each other out.
General Chemistry I CHM 111
Dr Erdal Onurhan
Slide 4
Atoms, Molecules, and Ions
Millikan’s Experiment
Millikan studied the
motion of single tiny
drops of oil that
picked up static
electricity from ions
suspended in air
through a
microscope and
arrived at a value for
electronic charge.
General Chemistry I CHM 111
Dr Erdal Onurhan
Slide 5
Atoms, Molecules, and Ions
Rutherford’s Experiment
-particles are produced by radioactive sources and they are positively charged.
Rutherford used very thin gold foils.
General Chemistry I CHM 111
Dr Erdal Onurhan
Slide 6
Atoms, Molecules, and Ions
Rutherford’s Model of the Atom
General Chemistry I CHM 111
Dr Erdal Onurhan
Slide 7
Atoms, Molecules, and Ions
Structure of the Atom and Relative Size
General Chemistry I CHM 111
Dr Erdal Onurhan
Slide 8
Atoms, Molecules, and Ions
Fundamental Properties of Subatomic Particles
*The column entitled ‘Mass (amu)’ is a measure of relative mass and will be
discussed later.
The above discussion shows that an atom is composed of three types of subatomic particles. These, in turn, are not differentiable from one atom to
another. They are exactly the same whatever the source is, i.e. they are
fundamental building blocks of any atom.
General Chemistry I CHM 111
Dr Erdal Onurhan
Slide 9
Atoms, Molecules, and Ions
Atom Symbolism
A
Z
X
X is the symbol for the element
General Chemistry I CHM 111
Dr Erdal Onurhan
Slide 10
Atoms, Molecules, and Ions
Periodic Table
Rows are
termed as
Periods
Columns are
termed as
Groups
General Chemistry I CHM 111
Dr Erdal Onurhan
Slide 11
Atoms, Molecules, and Ions
Formulas and Models
General Chemistry I CHM 111
Dr Erdal Onurhan
Slide 12
Atoms, Molecules, and Ions
Some Organic Functional Groups
- OH Alcohols
- COOH Acids
-OEthers
- CO- Ketones
- CHO Aldehydes
- NH2 Primary Amines
General Chemistry I CHM 111
Dr Erdal Onurhan
Slide 13