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Section 2.1 Evolving Theories of Matter
The Stone Age (~8000 BC)
• Metals had not yet been discovered.
• Rock and bone were used to construct tools.
• In the Middle East people learned to make and control fire
and to change a variety of substances to meet their needs.
• They cooked food, hardened mud, brick and tools to make
them tougher and eventually made glass and ceramics.
Interest in Metals and Liquids (6000-1000 BC):
• Early chemists investigated only materials thought to be
valuable.
• Gold – its properties of luster, color, lack of tarnishing and
softness made it a valued material used for jewelry and later
coins. It was not strong enough, however, to be used for tool
or weapons.
• Copper – though brittle when untreated, once heated it
becomes useful to make pots, coins, tools and jewelry. It can
be rolled into sheets or stretched into wires. Heating copper
and tin together lead to the creation of bronze, an alloy of the
two metals.
• Iron – the Iron Age began when the Hittites in the Middle East
extracted iron from stone to make very strong tools and
weapons. Later, iron was mixed with carbon to produce steel
and used to make even harder and sharper blades and armor.
• Liquids – the word “chemistry” can be derived from the Greek
word khemeia meaning juice of a plant. Many cultures
experimented with ways to extract and use juices and oils.
The Egyptians preserved the dead by wrapping them in cloths
soaked in pigments and resin from the juniper plant.
The Greek Philosophers (2500 years ago):
• The Greeks believed all matter was made up of tiny particles.
• In about 400 BC, the philosopher Democritus used the word
atomos (indivisible) to describe the smallest particle of a
substance that could not be broken up any further.
• He believed different substances were made up of different
types of atomos, giving each substance its own unique
properties.
• By mixing atomos, you could make new materials with their
own unique properties.
• In 350 BC, Aristotle stated that matter was made up of earth,
air, fire and water. Because he was a more well known and
respected philosopher his ideas were supported for the next
2000 yrs.
From Alchemy to Chemistry
• For the next 2000 years, experiments with matter were done
by alchemists who were part magician and part scientist.
• They were not interested in understanding the nature of
matter, but did perform some of the first chemistry
experiments.
• They created some of the chemistry tools we use today in
labs such as beakers and filters.
• They also made some practical discoveries, such as plaster of
Paris, used today to hold broken bones in place as they heal.
From the 1500’s: The Modern Scientist
• Scientists began to investigate the world around them to gain
knowledge about the nature of matter and based their
theories on observations and experimentation.
• Robert Boyle (in the 1660’s) experimented on gases and
became convinced that Democritus was correct, matter was
made up of tiny particles.
• In the 1770’s, Antoine Laurent Lavoisier and his wife Marie
studied chemical interactions and devised a system for
naming chemicals so that all chemists could use the same
names to describe their observations (eg. hydrogen, carbon,
oxygen).
The Beginning of Atomic Theory
John Dalton’s Billiard Ball Model (1808)
• suggested matter was made up of elements (pure substances
that contain no other substances).
• Each particle is called an atom.
• Every atom of the same element has the same mass, and
atoms of different elements have different masses.
• His model was called the “billiard ball” model since he
thought each atom was a solid sphere.
J. J. Thomson’s Raisin Bun Model (1897)
• First person to discover a sub-atomic particle (a particle
smaller than an atom).
• Thomson conducted a series of experiments with cathode ray
tubes leading him to the discovery of electrons.
• He proposed that the atom contained a positively charged
sphere in which negatively charged electrons were
embedded, like raisons in a bun.
• Overall, the atom had no charge.
• In 1904, Hantaro Nagaoka refined this theory of the atom
suggesting that electrons orbited a large central positive mass.
See Figure 2.15 (p.119).
• Support for this model came from a British scientist at McGill
University in Montreal, Canada named Ernest Rutherford.
Ernest Rutherford
• Introduced the idea of the nucleus.
• Rutherford shot positively charged particles through thin gold
foil.
• Instead of traveling straight through, some of the particles
were deflected.
• Conclusion: the atom must be composed of a very small core
of positively charged particles called the nucleus 1/10 000th of
the size of the atom. The nucleus deflected the positive
particles.
The Bohr Model (1922)
• electrons do not orbit the nucleus randomly, but rather in
specific circular orbits, or electron shells (see Figure 2.18, p.
120).
• electrons can jump from one shell to another by gaining or
losing energy.
• His model was accepted with refinements by James
Chadwick. Chadwick suggested the nucleus was made up of
positively charged protons and neutral particles called
neutrons.
• Today, most people still use the Bohr model to describe
atoms.
• Quantum mechanics research has found that
electrons exist in a charged cloud around the
nucleus
• (see Figure 2.19, p.120).
In Summary
• Dalton’s Billiard Ball : Matter is made up of solid
spheres called atoms
• Thomson’s Raisin Bun: Electrons are embedded in
the atom
• Rutherford: The nucleus is composed of protons
• Bohr: Electrons exist in orbitals
• Quantum Mechanics Theory: Most current accepted
atomic theory.
Section 2.2 Organizing the Elements
Looking for Patterns
•By the late 1700’s, only 7 metallic elements were known and
each was represented by a symbol of the Sun or a planet (see
Figure 2.21, p. 123).
•By the early 1800’s, more than 30 elements had been
discovered and more and more were identified thereafter.
•The need for a common classification system was apparent.
• John Dalton developed a new set of symbols for the
elements.
Dalton’s Short Lived Elemental Symbols
• His system was soon displaced by a system of symbols using
letters of the alphabet developed by Jons Jacob Berzelius in
1814. Now chemists had a common “language”.
• Atomic mass was used to arrange the elements in a pattern.
• Atomic mass refers to the mass of one atom of an element
and it is measured by atomic mass units or AMU.
• Chemist John Newlands first recognized a pattern in 1864.
• when the elements were arranged in increasing atomic mass
it seemed as though the properties of the elements repeated
at regular intervals, a pattern he called the “law of octaves”.
• Dmitiri Mendeleev organized the elements in a way that
reflected these common properties.
• He wrote all the properties of each element known at the
time on a card and laid them out on a table to find a pattern.
• He came upon a layout that followed an increasing atomic
mass and seemed to group elements with similar properties
(see Figure 2.23, p 124).
• There were gaps in his chart of elements. He predicted these
gaps were elements that had not yet been discovered.
• Other scientists were skeptical, but within 16 years many of
those gaps were filled.
Now here’s a little song about the elements.
"The Elements". A Flash animation
• Enjoy!
Section 2.3 The Periodic Table
• Period – horizontal row, numbered 1 to 7
• Group or Family – vertical row, numbered 1 to
18, elements in the same group have similar
properties
The Periodic Table tells us Many Things About
the Elements
11
23
Na+
sodium
•
atomic mass
atomic number
symbol
name of element
Element Symbol and Name
• a capital letter followed by a lower case letter,
usually an abbreviation of the element’s name.
• Some elements have a Latin name (potassium’s
Latin name is kalium, so its symbol is K).
• Other elements are named after the location in
which they were discovered (califorium)
• Others are named after the discoverer
(einsteinium).
• See the Table on page 128.
Atomic Number
• # of protons in the nucleus of an atom (ie.
oxygen always has 8 protons in its nucleus).
• Also indicates the # of electrons in the atom,
since all atoms are neutral in charge.
• (Note: the atomic number increases by 1 from
left to right across the periodic table.)
Atomic Mass
• total mass of the protons and neutrons in an
atom’s nucleus.
• An electron’s mass is so little, it is negligible when
calculating the atomic mass.
• The atomic mass is an average mass – the mass
varies according to how many neutrons are
present in each atom.
• The mass is measured by atomic mass units
(amu).
• Protons and neutrons each have an amu of 1
Mass Number
• # protons + # neutrons in an atom
• mass number can be used to discover how
many neutrons are in an atom:
mass # – atomic # = # of neutrons
• How many protons are there in an
oxygen atom?
• How many electrons?
• How many neutrons?
• How many protons are there in an
oxygen atom?
8
• How many electrons?
8
• How many neutrons?
16 – 8 = 8
• How many protons are there in a silicon
atom?
• How many electrons?
• How many neutrons?
• How many protons are there in a silicon
atom? 14
• How many electrons? 14
• How many neutrons? 28 – 14 = 14
• How many protons are there in a nitrogen
atom?
• How many electrons?
• How many neutrons?
• How many protons are there in a nitrogen
atom? 7
• How many electrons? 7
• How many neutrons? 14 – 7 = 7
• Do Skill Practice P.129
– Organize your answers into a chart. Use the atomic mass on your periodic
tables for all calculations rounded to nearest whole number.
Element
Vanadium
Nickel
Phosphorous
Bromine
Beryllium
Argon
Magnesium
Uranium
Silicon
Chromium
Titanium
Protons
Electrons
Neutrons
Answers to Skill Practice P.129
Element
Protons
Electrons
Neutrons
Vanadium
23
23
28
Nickel
28
28
23
Phosphorous
15
15
31
Bromine
35
35
45
Beryllium
4
4
5
Argon
18
18
12
Magnesium
12
12
12
Uranium
92
92
146
Silicon
14
14
14
Chromium
24
24
28
Titanium
22
22
26
Patterns in the Periodic Table
• metals:
• To the left the staircase line.
• shiny, malleable, ductile, and conduct electricity.
• All are solids at room temp. except Hg
• non-metals:
• To the right of the staircase line.
• Can be solids, liquids or gases at room temp.
• dull, brittle and do not conduct electricity.
• Surrounding the staircase are the metalloids: these
elements display both metal and non-metal properties.
Periods
• The period number tells you how many energy
levels you have.
• Periods 6 and 7 have 14 additional elements that
are listed at the bottom of the periodic table so it
is easier to print the table on a standard page.
• Properties change in 2 ways as you move from
left to right across a period:
– The elements change from metal to non-metal
– The elements become less reactive.
Groups
• A group is named for its first element, ex.
group 10 is the nickel group. Elements in the
same group have very similar properties.
• Group 1 – is divided into hydrogen and the
alkali metals. These are the most reactive
metals and they react violently in air or water.
Reactivity increases as you move down the
group
Reactions with Water
Brainiac Alkali Metals Video
• Group 2 – are the alkaline-earth metals.
These metals also react with air and water, but
are less reactive than alkali metals.
• Group 17 – are the halogens and are the
most reactive of the non-metals. They tend to
combine with other elements to make
compounds.
Halogen reactions
video
• Group 18 – are the noble gases and are the
most stable and unreactive of the elements.
• Do Check and Reflect P.134 # 1-5, 7-9
• Do Section Review P.136 # 2,3,4,6,8,10
Web Elements.com