Chemistry For Freshmen
Chemistry For Freshmen
Chemistry For Freshmen
Structure of Atom
What is an Atom?
The basic unit of matter. Also, it is the
defining structure of elements.
The defining structure of elements.
1850'S
Atoms actually possess internal structure.
They are made up of even smaller particles,
which are called subatomic particles. This
research led to the discovery of electrons,
protons, and neutrons.
Dalton's atomic theory
1. All matter is composed of indivisible and
indestructible atoms which are tiny, hard spheres.
2. All the atoms of any one element are identical; the
atoms of different elements are different and have
different properties (including different masses)
3. When matter undergoes changes, whether physical
or chemical, the atoms are merely rearranged. No atom
is created or destroyed.
4. Atoms of different elements combine in a definite
ratio of small whole numbers to form compounds
which are composed of compound atoms.
validity of the atomic theory
1. Unique behavior of each element.
2. Compounds have a definite composition, regardless of
how the samples were prepared or where originated. (Law
of definite proportion or composition)
3. During a physical or chemical change, the total mass
of all substances before and the total mass of all
substances after the change are the same. (Law of
conservation of mass)
Discovery of electrons
Michael Faraday
About 150 years ago, Michael Faraday
discovered the first cathode-ray tube when
he passed electricity through glass tubes from
which most of the air had been evacuated.
in all atoms.
Concept behind the cathode ray tube
The cathode ray (green light) bends towards the
positive plate (the red one) because it consists
of negatively charged particle that attracts the
positive pole of a magnet. The cathode ray
(green light) bends against the negative plate
(the silver one) as expected since negative
charged particle will repel to the negative pole
of a magnet.
CHARGE OF THE ELECTRON
Robert Milikan
3. 1909, He measured the charge of the
grams
6. The charge ratio of electron is 1 . 759 x
108 C/g
J.J. Thompson
7. He measured the charge of the electron
Quarks
What is a quark?
A quark is a tiny particle which makes up protons
and neutrons. Atoms are constructed of two types of
elementary particles: electrons and quarks.
11. After the invention of the particle accelerator, it
was discovered that electrons are fundamental
particles, but neutrons and protons are not.
Quark Theory of Atom known as
elementary particle.
This theory was proposed by physicists Murray Gell-
Mann and George Zwieg of California Institute of
Tech
There are six types or flavors of quarks, namely:
up, down, strange, charmed, bottom and top.
12. The proton is a combination of 3 quarks, two up
(ddu).
14. Particles that are composed of 3 quarks are known
collectively as baryons.
15. Particles that are composed of two quark are
known as mesons.
16. Particles that are not made up of quarks are called
leptons
17. Quarks cannot be separated from each other. They