Transcript ALL MATTER IS MADE UP OF TINY PARTICLES CALLED “ATOMOS”

ATOMIC THEORY
Building blocks of matter
DEMOCRITUS
• IN 400 BC,DEMOCRITUS SAID:
• ALL MATTER IS MADE UP OF TINY
PARTICLES CALLED “ATOMOS”
The Greek Periodic Table
• - Aristotle: Matter had no properties itself,
but that various combinations of simple
properties made every substance known.
• 4 properties were: moist, cold, dry, hot
• 4 elements:
– Water, earth, fire, air
300 BC, Aristotle:
The Greek periodic table
• Greek theories were philosophical and
moralistic
• Did nothing to suggest a direction for
experimental work
1808 Dalton’s atomic theory
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1. All matter is made up of atoms
2. Atoms of the same element are alike.
3. Atoms of different elements are different.
4. Compounds have a definite composition
and combine in small whole number ratios.
• 5. Chemical Reactions involve the reshuffling
of the atoms in a compound to make new
compounds.
• 6. Atoms cannot be subdivided.
LAWS FROM ATOMIC
THEORY
• 1. Law of conservation of matter
– Mass of reactants = mass of products
– mass cannot be created nor destroyed
– For example, if you were told that 4 grams of
hydrogen reacted with some oxygen to make 36
grams of water then you could figure out how
much oxygen must have been used by applying
the law of conservation of mass.
– hydrogen + oxygen = water
– 4g
+
? = 36 g
– ? = 36 - 4 = 32
So 32 grams of oxygen were used
LAWS FROM ATOMIC THEORY
• 2. Law of definite proportions
– AKA Law of constant composition
– Every pure sample of a particular
compound always contains the same
proportion by mass of the elements in the
compound
– the relative amount of each element in a
particular compound is always the same
• H2O, will always have the same percent by
weight, e.g. 11.2% H and 88.8% O
LAWS FROM ATOMIC THEORY
• 3. Law of multiple proportions
– when elements combine, they do so in the
ratio of small whole numbers
– carbon and oxygen react to form CO or
CO2, but not CO1.6
PARTICLES OF THE ATOM
• ELECTRON- JJ THOMPSON/1897 (plum pudding)
• Atoms contain – charged particles (corpuscles) electrons
• Atoms contain + charged particles later called
protons
• An atom is electrically neutral
– Atoms need – and +
• Thought of the atom as a positive charged ball with
negative charges throughout. (Plum
pudding/Chocolate chip cookie)
How did Thompson do it?
– a cathode ray tube consists of a gas-filled
glass tube in which two metal plates, one
negatively charged (the cathode) and the
other positively charged (the anode), have
been placed. When a very large voltage is
placed across the electrodes, the neutral
gas inside the tube will ionize into a
conducting plasma, and a current will flow
as electrons travel from the cathode to the
other side.
Rutherford - Bohr
– PROTON AND NUCLEUS- RUTHERFORD/
1911 (gold foil experiment)
Rutherford
• Alpha, beta and gamma particles
• Alpha particles – Helium atoms
• Beta particles – high energy electrons
emitted directly from the nucleus
• Gamma particles is high energy radiation
given off by the nucleus
Rutherford’s accomplishments
• Identified alpha, beta, and gamma
particles
• Showed that new elements were formed
as a result of radio active decay of an
element
• Showed that alpha particles were really
helium ions (He2+)
• Discovered the atomic nucleus (Gold foil)
– Most alpha particles pass through (atom is
mainly space)
– Some bounce straight back (hit something
heavy) – the nucleus
– Nucleus contained all the protons and most of
the mass of an atom
• Predicted the existence of the neutron –
Neutron found by Chadwick in 1932
The atom
Particle
Symbol
Charge Molar
Mass
Found
Particle
Symbol
Charge Molar
Mass
Found
Electron e-
-1
0.000 549 Outside
nucleus
Proton
p
+1
1.007 825 Inside
nucleus
Neutron
n
0
1.008 665 Inside
nucleus
• Borh explained behaviour of electrons
outside the nucleus
• He explained that the electrons orbited the
nucleus of an atom
• Therefore Rutherford-Bohr model
• Couldn’t make model work with atoms with
more than 1 electron, but it is still a good
model for understanding atomic structure
– NEUTRON-CHADWICK / 1932
– Electron Shells/ Bohr / 1913