Download Science 9 Unit B 2.0 - Vegreville Composite High

Section 2.0
An understanding of the nature of
matter has developed through
observations over time.
Goals for this Section:
1. Describe ancient theories of matter and
chemical change
2. Distinguish between observation and theory
3. Describe the different models of the structure
of the atom
4. Identify patterns that are used to group
elements
5. Describe the arrangement of atoms within the
periodic table
6. Use the periodic table to describe the
properties of individual atoms
7. Explain relationships within periods and
groups within the periodic table
2.1 – Evolving Theories of
Matter
• We could consider stoneage people to be the very
first chemists
• They learned to use fire
as a tool to produce
chemical changes that
made their lives easier
http://www.mrdowling.com
Early Interests in Metals &
Liquids
• Until about 1000 B.C.,
chemists only investigated
materials that had high
value to humans
• Most of these materials
were metals, such as gold,
copper, and iron
• Other substances of
interests were liquids such
as oils and plant juices
http://www.shee-eire.com
The Idea of the Atom
• The first scientist to suggest an idea of
an atom was Democritus, in about 400
B.C.
• He suggested that all matter was made
up of very small, indivisible particles
known as atomos
• However, another Greek philosopher had
a more popular idea…
Earth, Wind & Fire (… and
Water)
• Aristotle suggested that all materials
contained different proportions of four
elements – Earth, Wind, Fire, and Water
• This idea was the preferred theory about
the composition of matter for about 2000
years
http://www.britannica.com
Alchemy
• Alchemy was a
field of study
where the
“scientists”
attempted to
find elixirs that
would extend
life, or to
develop a
method of
turning base
metals into gold
http://hem.fyristorg.com
Alchemy and Chemistry
• In fact, some of the most famous
alchemists were in fact good con-men
who managed to convince nobles to
provide them with money in return for
recipes for creating gold from base
metals
• However, these alchemists did contribute
to what we now know as legitimate
chemistry
• Many of the chemical reactions that were
used by alchemists are now used by
chemists, and much of the specialized
apparatus that is used in chemistry was
developed by alchemists as well
http://www.powerlabs.org
The Modern Chemists
• Early chemists like Robert Boyle and
Antoine Lavoisier began to develop
theories about matter and reactions
based on observations and experiments
• Eventually, by the 1800s, an atomic
theory began to take shape
Dalton’s Model
http://192.107.108.56
http://turing.kingsu.ca
J.J. Thomson’s Experiment
http://www.lightandmatter.com
Thomson’s Model
Rutherford Scattering
Rutherford’s Model
http://www.osa.ceu.hu
Bohr & Atomic Spectra
http://outreach.atnf.csiro.au
The Bohr Model
http://education.jlab.org
Modern Models
http://static.howstuffworks.com
2.2 – Organizing the
Elements
• Rather than using
names for
chemicals early
scientist used
symbols for the
elements that they
knew
• Scientists tried to organize elements
by using their properties, however,
this was difficult because different
scientists used different properties
• John Dalton first attempted to
categorize and order the elements in
the early 1800’s. He developed a new
system of symbols
Jöns Jacob Berzelius
• In 1814 Berzelius suggested using
letters rather than symbols
• the first letter is capitalized
• if two elements had the same first
letter (like Hydrogen and Helium) then
the second letter would be used
• this system is still in use today
The Evolution of Symbols
Ordering the Elements
• order for the elements was soon discovered
by using the atomic mass as a means to list
them
• scientists could establish the average mass
of an atom by comparing it to the mass of a
carbon atom
• in 1864 John Newlands recognized that
there was a pattern of repeating properties
within the elements when they were listed
in increasing mass
Dimitri Mendeleev
• Dmitri Mendeleev arranged elements
by their chemical properties
• When he did this, a clear pattern
emerged
• There were holes in his pattern
created by undiscovered elements
• These holes were filled over time –
showing that Mendeleev’s table was
accurate
2.3 – The Periodic Table
Divisions Within the
Periodic Table
• The table can be divided into horizontal
rows (periods) or vertical columns
(groups or families)
• Each box within a periodic table contains
important information
Useful Information on Each
Elements
8
2-
O
oxygen
16.0
Atomic Mass and Isotopes
• The atomic mass of an element provides
you with the total mass of the protons
and neutrons in an atom
• However, you will notice that not all
atoms have atomic masses that are
whole numbers
• Because you cannot have fractions of
protons and neutrons, what is happening
here?
• It turns out that the atomic mass is the
average weighted mass of different
isotopes of an atom
• For example, there are three different
isotopes of hydrogen:
http://images.encarta.msn.com
Protons + Neutrons =
Atomic Mass Fun!
• We can determine the number of protons
and neutrons in the nucleus of an atom
by using its atomic number and its atomic
mass
# of Protons (Atomic Number)
+ # of Neutrons
_______________
Atomic Mass
Example: Number of Protons
& Neutrons in Uranium
• Uranium has an atomic mass of 238.0.
How many protons and neutrons are
present in this element?
Metals & Nonmetals
• There are two major groups of elements
in the periodic table – the metals and the
nonmetals
Metals
http://www.britannica.com
• Properties:
Nonmetals
• Properties:
http://www.britannica.com
Groups
• There are 18 groups on the modern
periodic table
• The elements that make up a particular
group typically have similar reactivity and
often engage in the same reactions and
form similar products
Periods
• Periods are repeating patterns of
elements created by the separation of
elements into their groups
• The atomic mass of elements increases
as you move from left to right along a
period
General Reactivity of
Elements
Group 1 – Alkali Metals
• These are the most reactive metals
• They will react when exposed to air or
water
• Typically will not be found in their
elemental state in nature
http://www.webelements.com
Group 2 – Alkaline Earths
• Reactive metals, although their reactivity
is much lower than the alkali metals
• React readily with air and water
• Many are combustible
http://upload.wikimedia.org
Group 17 – The Halogens
• These are the most reactive nonmetals
• They are all diatomic, meaning that in
their natural state, two atoms of the
element are bonded together
http://en.wikipedia.org
Group 18 – The Noble
Gases
• These gases are all very stable – in fact,
until 1962 it was believed that they would
not react at all
http://en.wikipedia.org