Download Unit B - Topic 2.0 Notes

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 new 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
• 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, see p27
• 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. 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 also 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.
• http://www.youtube.com/watch?v=nsbXp64YPRQ
Mendeleev
Now here’s a little song about the elements.
"The Elements". A Flash animation
Just How Small is an Atom?
Which Periodic Element Are YOU??
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
22.99
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 (californium)
• 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
• Periodic Table Battleship!!
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
francium in ocean
• Group 2 – are the alkaline-earth metals.
These metals also react with air and
water, but are less reactive than alkali
metals.
http://www.youtube.com/watch?v=aeb8H0
WDuQo
• Group 17 – are the halogens and are the
most reactive of the non-metals. They
tend to combine with other elements to
make compounds.
halogens
• Group 18 – are the noble gases and are
the most stable and unreactive of the
elements.
noble gases
• Do Check and Reflect P.134 # 1-5, 7, 8, 9
• Do Section Review P.136 # 2,3,4,6,8,10
Web Elements.com