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Chemistry
Chapter 4
- Many philosophers concluded that matter was composed of things such as earth,
water, air, and fire. It was also commonly accepted that matter
could be endlessly divided into smaller and smaller pieces.
-Democritus:
•Wast he first person to propose the idea that matter was not
infinitely divisible.
•He believed matter was made up of tiny individual particles
called atoms.
•He believed that atoms could not be
created, destroyed, or further divided.
-Aristotle:
•He rejected the notion of atoms because
it did not agree with his own ideas about
nature.
•Atoms moved through empty Space,
NOT.
-Dalton:
•He was able to use experiments to
determine the mass ratios of the
elements involved in those reactions.
-Law of conversation of mass
states that mass is conserved
any process, such as a chemical
reaction.
-Dalton’s atomic theory easily
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explains that the conservation of mass in chemical reactions it he result of the
separation, combination, or rearrangement of atoms-atoms that are not created,
destroyed, or divided in the process.
- Atoms of the same element can have slightly different masses.
- Section 1 Review:
• Democritus was the first person to propose the existence of atoms.
• According to Democritus, atoms are solid, homogenous, and indivisible.
• Aristotle did not believe in the existence of atoms.
• John Danton’s atomic theory is based on numerous scientific experiments.
- Smallest particle of an element that retains the properties of element is called an
atom.
- Atoms can be views using Scanning tunneling microscope (STM).
- The cathode-ray tube and Sir William Crookes:
•A green flash was produced by some form
of radiation striking a zinc-slide coating that
had been applied to he end of the tube.
•This ray, originating from the cathode and
traveling to the anode, was called a
cathode ray.
•The accidental discovery of the cathode
ray led to the invention of the TV.
•Cathode rays were a dream of charged
particles.
•The particles carried a negative charge.
(The exact value of the negative charge was not known.)
• Negatively charge particles that are part of all forms of matter are now known as
electrons.
- Charge-to mass ratio:
2
•
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Thomson was able to determine the charge-to-mass ratio of the charged particle.
• Thomson concluded that the mass of the charged particle was much less than that
of a hydrogen atom, the lightest known atom.
- The oil-drop experiment and the charge of an electron:
•Robert Milikan determined the
charge of an electron using the
oil-drop apparatus.
•He was able to determine the
magnitude of the charge on each
drop increased in discrete
amounts and determined that the
smallest common denominator
was 1.602*10^-19, he identified this numbers as
the charge of the electron.
•A single electron carries a charge of 1-.
-Mass of an electron is 1/1840
-JJ Thomson proper a model of the atom that
became known as the plum pudding model.
-In 1911, Ernest Rutherford began to study how
positively charged alpha particles interacted with
solid matter.
-Rutherford concluded that the plum pudding model
was incorrect because it could not explain the results of the gold foil experiment.
- He calculated that ann atom consisted mostly of empty space through which the
electrons move.
- He also concluded that almost all of the atom’s positive charge and almost all of its
was were contained in a tiny, dense region int he center of the atom, which he called
the nucleus.
- A proton is a subatomic particle carrying a charge equal to but opposite of an election;
that is, a proton has a charge of 1+.
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-A neutron is a
subatomic
particle that has
a mass nearly
equal to that of
a proton, but it
carries no
electric charge.
-Section 2
Review:
•An atom is the
smallest parties
of an element that maintains the
properties of that element.
•Electrons have a 1- charge, proton
have a 1+ charge, and neutron have
no charge.
•An atom consist mostly of empty
space surrounding the nucleus.
-Atomic number: The
number of protons in an
atom.
-Atoms with the same
number of protons but
different numbers of
neutrons are called
isotopes.
-The mass number is
the sum of the atomic
number and neutron in
the nucleus.
- Atomic mass unit (amu) is defined as one-twelfth the mass of a carbon-12 atoms.
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Atomic mass of an element is the weighted average mass of the isotopes of that
element.