Chapter 3 – Atoms: The Building Blocks of Matter
Section 3-1 – The Atom: From Philosophical Idea to Scientific
Theory
The first people to think about particle theory were the _____________ around
___________.
Greeks
400 BC
One in particular was __________. The word atom in
Greek means _______.
Democritus
indivisible
Following Democritus was _________. He didn’t believe in atoms. He thought matter was
___________.
Aristotle
continuous
This idea succeeded for about _______years. Neither view
was supported by __________ _________ until ________.
2000experimental evidence
The 18th century
By the late ________, most people thought of an _______ as
something that could not be broken down and that could _________
with other elements to form __________.
1800’s Atom
combine compounds
Scientists still weren’t sure, however if they always combined in the same
________.
proportions
In the late 1790’s scientists had better _________ which allowed
them to study chemical reactions ___________.
balances
quantitatively
This led to the law of _______________________. It essentially says that as long as
nothing enters or leaves a chemical reaction, _______ remains
constant.
conservation of mass
mass
Antoine-Laurent de Lavoisier
• He was obsessed with measuring mass during chemical reactions.
• He observed that when chemical reactions are carried out in a closed system, the mass of the system is not changed.
• He was obsessed with the latest equipment for measuring mass.
• He spent a great deal of the French taxpayers money on this equipment.
• He died in the French Revolution.
It also lead to the law of __________________ which
essentially says that regardless of the _________ or _________ of
the sample, the elements that make it up are always there in the same
____________.definite composition
size or sourceproportions
Law of Definite Proportions
Joseph Louis Proust observed that Copper carbonate (CuCO3) occurs in nature
as the mineral malachite (a), it forms as a patina on copper roofs (b) and bronze
statues, and can also be synthesized in the laboratory (c). Regardless of its
source, basic copper carbonate has the same composition.
Joseph Louis Proust (1754-1826)
Since the composition of copper carbonate is the identical regardless
of the source, Proust called this generalization as the law of definite
proportions.
Swedish chemist Berzelius
heated certain amount of lead
with various amount of sulfur. He
found that when he used 1.55 g of
sulfur (yellow) and 10.0 g of lead
(gray) he got 11.55 of lead sulfide
(black).Jons Jacob von Berzelius
1779-1848
If sulfur were taken in excess of 1.55g, Berzelius found that the excess
amount of sulfur did not react. Similarly if had 1.55 g of sulfur and added
lead in excess of 10.0 g, he found that the excess lead did not react
The law of definite proportions – Berzelius View
Definite proportions – A Closer Look
The law of definite proportions. Berzelius' experiment with lead and sulfur
are interpreted in terms of Dalton's atomic theory.
The electrolysis of water
Electrolysis of water. During electrolysis,
water decomposes to give hydrogen gas
and oxygen gas always in a 2-to-1 volume
ratio when energy is supplied by a battery
or other source of direct current (dc).
http://wps.prenhall.com/wps/media/objects/439/449969/Media_Portfolio/Chapter_04/Electrolysis_of_Water.MOV
Henry Cavendish (1731 - 1810) further
illustrated the law of definite proportion
by electrolyzing water.
More complicated is the law of ______________. It says that if ______ or
more different _______ are made of the same 2 elements, the ratio of the ________ element combined with a fixed mass of the 1st element is always a ________ of small
___________ numbers
multiple proportions two2nd ratio
whole
An example of this would be the compounds of ___________
and ___________.
carbon dioxide
carbon monoxide
John Dalton’s Atomic Theory of Multiple Proportions
John Dalton John Dalton (1766-1848)(1766-1848)
Dalton theory multiple proportions:
Elements can combine with each other
in more than one set of proportions.
For example, hydrogen and oxygen
combine with each other in two different
proportions and form two entirely
different compounds.
Water
OH2OH2 222 peroxideHydrogen
OH2O2H2 2222
Although these two
molecules contain only
hydrogen and oxygen,
they are not the same
compound.
These three laws prompted John Dalton to propose his
atomic theory. It basically says:
1. All matter is made of ______________
______________ called ____________
indivisibleindestructible
atoms
2. Atoms of the same ___________ are chemically and physically the ________.
element
same
3. Atoms of ___________ elements are chemically and
physically the ________.
different
different
4. When atoms _______ in a chemical reaction, they do so in ___________, ____________
number ratios.
combinesmall whole
In a chemical reaction, atoms aren’t ____________ or
____________, they are simply _____________.
createddestroyedrearranged
Section 3-2 – The Structure of the Atom
Atoms consist of ___________________ regions.
One of them contains the ___________________ and
___________________. It is called the ___________________.
2protons neutrons
nucleus
The other area surrounds the nucleus. It contains
___________________ particles called
___________________.
negatively charged
electrons
Actually ___________________,
___________________, and ___________________ are all
___________________.
protons neutrons
electrons subatomic particles
The electron was discovered by working with a tube that
contained a ___________________ at very
low pressure.
gas
When ___________________ passed through it, it would light
up. It is called a _________________________
____________.
an electrical current
cathode ray tube
The fact that the ray was deflected by a negative charged
showed that the ray had a ___________________ charge.
negative
The fact that the ray could move a paddle wheel demonstrated the ___________________
nature of the ray.
particle
The ray was actually made of ___________________.
electrons
The scientist credited with naming the
___________________ was ___________________.
electron
JJ Thomson
It stands to reason that where there is a negative charge, there
must be a ___________________ charge
to balance it.
positive
_________________________ and associates tried to bombard
___________________ with ___________________.
Ernest Rutherfordgold
alpha particles
They expected that most of the α particles would
________________________.
go straight thru (92%)
For the most part, this was true, but some were ___________________ and a very small percentage were
actually _____________________.
deflected (6%)
shot straight back (2%)
It took 2 years, but Rutherford developed a 2 part explanation. It
was:
• Atoms are mostly empty space
• Atoms must have a densely packed positively charged nucleus.
To summarize the ___________________,
___________________ are the lightest and can be found
______________________. They have a ________________ charge.
subatomic particles electronsorbiting the nucleus
negative
___________________ and ___________________ are the heaviest and are found in the
___________________.
Protonsneutronsnucleus
___________________ have a positive charge and
___________________ have ___________________ charge.
Protonsneutrons
no
Section 3-3 – Counting Atoms
neutral, atomic number, chlorine, proton, 17, electron
A neutral atom of chlorine would have 17 protons and 17 electrons if it is neutral.
Because chlorine has an atomic number of 17, it would have 17 protons and assuming it is neutral, it would have 17 electrons.
isotope, tritium, deuterium, protium, atomic mass, 1, 2, 3, hydrogen
The three isotopes of hydrogen are protium with an atomic mass of 1, deuterium with an atomic mass of 2, and tritium with an atomic mass of 3.
Hydrogen has 3 different isotopes. They are protium, deuterium, and tritium with atomic masses of 1, 2, and 3 respectively.
nuclide, superscript, subscript, hyphen notation, uranium, nuclear
symbol
You can indicate nuclides 2 different ways; Hyphen notation means you write the symbol with a dash and the atomic mass or you could use the nuclear symbol method where you write the symbol and put the atomic mass as a subscript to the upper left and the atomic number as a subscript to the lower left.
Example
• U-238
U23892
carbon-12, atomic mass unit
An atomic mass unit is defined as one twelfth of a carbon-12 atom.
average atomic mass, isotopes, percentage, naturally occurring
The average atomic mass of an element takes into account the percentages of the naturally occurring isotopes.
Average atomic mass can be calculated by multiplying the atomic masses of the isotopes by their naturally occurring percentage in a mixture.
mole, carbon-12, Avogadro’s number, molar mass
A mole is defined as 12 g of the carbon-12 isotope. It has Avogadro’s number of atoms. The molar mass of all other elements is compared to a mole of carbon-12.
Subatomic Particles
The atoms of all elements consists of positively charged protons,
neutral neutrons and negatively charged electrons. The protons
and the neutrons together are called as nucleons and they are
located at the nucleus of the atoms.
The number of protons in the nucleus of an atom determines the
atomic number (Z) and indicates the element's identity. For a
neutral atom, the atomic number also describes the number of
electrons around the nucleus.
The Atomic Number
Atomic Mass and Atomic Number
Mass number A (sum of protons and neutrons)
Atomic number Z (number of protons)
= number of neutrons.
While the number of protons in the nucleus defines an element's
identity, variations on the number of neutrons in the nucleus give
rise to different isotopes of the same element.
Isotopes of hydrogen
Mass Numbers and Atomic Numbers
The atomic number is equal to the number of protons in an atom
of that element. The mass number is the sum of the number of
protons and neutrons.
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