Download Atoms - Chemistry Land

Chaos. That’s something we are all familiar with.
There’s even a movie called chaos. Life is full of it and
we all try to reduce it. We want to feel organized.
Few of us want the world to be chaotic.
Chaos goes beyond our lives and
our world. This writer addresses
chaos throughout the universe and
its stunning complexity.
Throughout human history, we have
tried to make more sense out of the
world around us. To reduce the
chaos, we tried to perceive a more
simpler underlying fabric of the
world.
Thales (600 B.C.)
In 600 B.C. the Greek philosopher
Thales proposed that everything in
the world was made from water.
Water was the only element. All
living things consume water and
perhaps water is creating all the
matter living things are composed
of.
Water
Xenophanes (500 B.C.)
Earth
Water
In 500 B.C. the Greek philosopher
Xenophanes felt water couldn’t be
the element for everything. It
seemed the world was made two
elements, earth and water.
Empedocles (440 B.C.)
Four elements
Earth
(more commonly called dirt)
Water
Fire
Air
60 years later Empedocles
felt the universe required four
elements. Earth, water, fire,
and air.
As leaves change their color,
you can see the fire that they
contain. Anything that burns
will reveal that it is made of
the four elements
(At this point, I crumpled
some paper and lit a match
to it.) Notice there is fire in
this paper. Also, I feel wind
rising from it. As I hold this
cold beaker above it, you can
see water condensing on it.
So the dry paper actually has
water in it. Finally as it burns
out you see the ashes, which
is like dirt or earth.
Democritus
Athens, Greece
400 B.C.
40 years later, Democritus
said, Ok there may be four
elements, but I believe these
elements are not as they
appear.
The mountains look solid and
the water seems smooth, but
that because there’s a limit to
our vision.
For example, from a
distance, we cannot see the
individual grains of sand that
this beach is made from.
However, up close we know
there are individual grains.
I think elements are like this.
They are made of individual
particles, that in huge
numbers become visible and
know to us.
The smallest particles of
matter are indivisible.
Since atomos is the Greek word
for “indivisible” I shall call these
particles “atoms”.
“Atoms” cannot be destroyed, so
there is conservation of matter.
I also believe that these small particles are indivisible. In other words, there is a
limit to how small matter can be broken. Since atomos is the Greek word for
indivisible I shall call these particles atoms. Atoms cannot be destroyed, so there
is conservation of matter. We may see water evaporate or wood burn, but the
matter or atoms are still around.
Aristotle
Athens, Greece
340 B.C.
Aristotle also had opinions
on chemistry. However,
Aristotle had the most
influence on the history of
chemistry.
About 60 years later, Aristotle also had opinions
on chemistry. However, he had the most
influence on the history of chemistry.
Besides chemistry, he also tackled physics, biology,
psychology, and logic.
It’s ironic that the theories of Aristotle which were
most accepted were also the most incorrect.
For example, he
proposed and embraced
the mystical fifth
element. It took
chemists 2,000 years to
recognize that there was
no mystical fifth element.
Aristotle disagreed
with Democritus
•Democritus said atoms cannot be divided.
•You cannot place restraints on the gods.
Therefore, matter cannot be made up of
indivisible particles. Atoms cannot exist.
The concept of the atom fell out of
favor for 2,000 years until…
Democritus’ view of what atoms might look like.
John Dalton
England
1796
John Dalton began teaching
when he was 12.
Dalton was a humble man with
several apparent handicaps: he
was poor; he was not articulate;
he was not a skilled
experimentalist; and he was
color-blind.
Dalton is best known for his atomic
theory, which revolutionized the
science of chemistry and brought
back Democritus’ concept of the
atom.
Elements are composed of minute,
indivisible particles called atoms
All atoms of that element are alike.
Plus those atoms are not like the
atoms of any other element.
Copper
Gold
Chemical compounds are formed
by the union of two or more atoms
of different elements.
Atoms combine to form
compounds in simple
ratios, such as 1:1, 1:2,
2:2, 1:3, and so forth.
Law of Definite
Proportions
Atoms of two elements may
combine in different ratios to form
more than one compound.
We call this:
The Law of Multiple Proportions
Reactions are just a
rearrangement of atoms.
Oxygen and hydrogen gas reacting to form water
Reactions are just a
rearrangement of atoms.
O
H
O
Ba
O
H
Ca
O S
O
O
Arranged from
light to heavy
by their relative
weights
Through experiments, Dalton was
getting rough estimates on the
relative weights of known
elements. The second is Azote,
“A” for no and “Zote” for life. The
gas was nitrogen, and living things
die if only breathing nitrogen.
Some were not elements. Lime is
actually calcium and oxygen
combined, but Dalton didn’t know
that.
Dalton’s Elements
This is the Swedish
chemist, Johan Berzelius.
Like Dalton, he was
finding the relative weights
of the elements.
Berzelius in credited for
the naming convention we
use for elements.
Johan Jacob Berzelius from Sweden
Berzelius’ Symbols for Elements
•Older elements take the symbol from their Latin name.
•Fe comes from ferrum not iron.
•Instead of G for gold he wants Au from aurum.
•Instead of S for Silver he wants Ag from argentum.
•Newer symbols come from English names.
•O comes from oxygen.
•2000 experiments over a ten-year period to determine
accurate relative atomic weights for all the elements now
known.
John Newlands
England
Researchers had already began
to arrange and classify
elements:
Metals vs. non-metals
In tables of increasing
atomic weight
John Newlands from England
had a different way to arrange
elements.
1867
Certain elements resembled one another in behavior.
Chlorine, bromine & iodine
• violently corrosive
• form acids
• Lithium, sodium, potassium
• Unite violently with oxygen or water
• Oxides form caustic aqueous solutions
Every eighth element have similar characteristics
Li Be B C N O F
Na Mg Al Si P S Cl
K
Ca ? ? As Se Br
I call this the “Law of Octaves”
“Law of Octaves”
He presented his theory to the
England Chemical Society and was
laughed at.
They said to arrange it alphabetically.
Dmitri Ivanovich Mendeleev
Russia
1871
Periodic Law
Here is someone you
don’t laugh at.
Like Newlands, he
used lithium, sodium,
and potassium plus the
chlorine family as
guide posts
Orginally Mendeleev arranged the
elements with common properties
in rows instead of columns. But
here are the two groups of
elements that acted as guide
posts.
His table helped
others find the
missing elements.
Gallium
Germanium
As a tribute to
Mendeleev, here is his
Periodic Table of the
Elements carved in
stone.
In an effort to
understand the chaos
around us, we found
order.
The complexity of the
universe is tamed by
this table. It represents
a comforting reminder
that chaos is not in
control.
Learning Check
Name an element that has similar
properties to chlorine (Cl).
Name an element that has similar properties
to sodium (Na).
Name an element that has similar properties
to copper (Cu).
For example Helium shows the atomic mass of 4.00 and Oxygen is 16.00.
That means that one atom of oxygen is 4 times heavier than helium. Oxygen
has 4 times more protons and 4 times more neutrons (not shown in table) that
account for this.
Learning Check
How many times heavier is a calcium
atom compared to a neon atom?
How many times heavier is a calcium
atom compared to a helium atom?
How many times heavier is oxygen
compared to carbon?
To understand it further we need to look
closer at the makeup of the atom.
It’s all
about
building
blocks
Evolution of the atom
Electrons (-)
Neutrons
Protons (+)
How do electrons “think”?
+
++
Electrons “dislike” other electrons
Electrons “love” protons
• Electrons are strongly attracted to protons.
The more protons present the stronger the
attraction.
+
Likes Repel
Opposites Attract
+ +
What do electrons do when both
protons and electrons are present?
They get as close to
the protons as
possible while
maintaining as much
distance as possible
from other electrons.
+
++` +
+
What would the right electron do?
+
What would electrons in two
hydrogen atoms do?
-
-
+
+
Remember this is a simplistic version of the electron.
Building elements
Hydrogen-1
Beryllium-4
Helium-2
Boron-5
Lithium-3
Carbon-6
Electrons are not the simple little particles that we
often draw them. They demonstrate the dual nature of
matter, which is both particle and wave. There shape
or location is quite flexible. In this shape there are two
lobes. The electron occupies both. Somehow is gets
back and forth without passing through the middle
space. Or it is in both locations at the same time.
Either way it is not a simple particle. Also, it’s location
is not fixed. The probability that it is in this region
being drawn is high, but there is a probability that it
can be farther away, even as far as the moon. An
extremely small chance, I agree, but it is possible. So
at this moment some of your electrons could be about
anywhere. So you can’t really say you never go
anywhere. But the main thing to remember is not to
underestimate the flexibility of electrons and their
amazing abilities. Electrons give atoms their diversity.
Atomic Number
Atomic number = number of protons in an atom
1
Atomic
Number
29
H
Cu
1.008
63.55
Hydrogen has
one proton.
Copper has 29
protons.
Learning Check
What is the atomic number of cobalt (Co)?
What is the atomic number of carbon (C)?
How many protons does uranium (U) have?
Mass number = the total number of
protons and neutrons in an atom
6+6
12
Mass Number
6+8
14
6
Atomic Number
6
C
Isotopes
C
Carbon-12 & Carbon-14
Isotopes have the same number of protons,
but different numbers of neutrons.
Learning Check
Naturally occurring carbon consists of three
isotopes, 12C, 13C, and 14C. State the number of
protons, neutrons, and electrons in each of
these carbon atoms.
12
C
6
13
6
C
14
C
6
# p _______
6
_______
6
_______
6
# n _______
6
_______
7
_______
8
# e _______
6
_______
6
_______
6
Practice Problems
Answer the questions about
the bromine-80 isotope.
80
35
Br
• How many protons are in the isotope?
• 35 protons
• What is the mass number of the isotope?
• The mass number is 80.
• How many neutrons are in the isotope?
• 80 (protons + neutrons) - 35 (protons) = 45 neutrons
Atomic Mass
Atomic Mass = weighted average of the mass
numbers of the isotopes of an element
12
Atomic #
C
12.01
Atomic
Mass
If most carbon atoms had
8 neutrons, then the
atomic mass would be
closer to 14.
Carbon has three isotopes
C-12, C-13, C-14 with mass
numbers of 12, 13, & 14
respectively.
Most carbon atoms have 6
neutrons, so they have a mass
number of 12. That is why
the average of 12.01 is so
close to 12.
Atomic Mass
Atomic Mass = weighted average of the mass
numbers of the isotopes of an element
1
Atomic #
H
1.008
29
Cu
Atomic
Mass
63.55
Hydrogen has three
isotopes: H-1, H-2 and H-3
Copper has two common
isotopes: Cu-63 and Cu-65
Which isotope is the most
plentiful?
Which isotope is the most
plentiful?
65
Zn
30
30
Learning Check
Zn
65.39
An atom of zinc has a mass number of 65.
A. Number of protons in the zinc atom
1) 30
2) 35
3) 65
B. Number of neutrons in the zinc atom
1) 30
2) 35.39
3) 35
C. What is the mass number of a zinc isotope
with 37 neutrons?
1) 37
2) 65
3) 67
Solution
An atom of zinc has a mass number of 65.
A. Number of protons in the zinc atom
1) 30
B. Number of neutrons in the zinc atom
2) 35
C. What is the mass number of a zinc isotope
with 37 neutrons?
3) 67
67
30
Zn
The number of outer electrons
(valence electrons) is shown by
the group number
Valence Electrons
These outer electrons are
called valence electrons.
(valens is Latin meaning to be
strong. The word valiant also
comes from valens). Valence
electrons give the elements the
strength to react with other
elements. Valence electrons
are given away, pulled in, or
shared. This results in two
elements combining or joining
with each other.
O
How do you recognize a metal?
This shows two defects on
a surface of copper. The
electrons form a “lake” on
the surface of the copper.
There are even waves.
This probably accounts for
the shiny property of
metals and its conductivity.
Conducts electricity
and are malleable
This is as far as I got.
Non-metals
•
•
•
•
•
Attract electrons (electronegative)
Hold tightly to electrons
More brittle
Lighter
More apt to be gas even when combined
with other non-metals.
• Form salts when combined with metals
One or more non-metals bonded to one or
more metals. Usually water soluble.
Lithium-Li, Sodium-Na, Potassium-K, Rubidium-Rb, Cesium-Cs
Rock
Soda
Pot Ashes
Red
Sky blue
See page 79 in textbook for more origins of element names.
The ashes of the plant were
found to neutralize acids.
Anything that can neutralize
acids is now called “alkaline”
H2O
Sodium hydroxide and potassium hydroxide
found in the ashes of the plant.
Beryllium, Magnesium, Calcium, Strontium, Barium, Radium
These metals, when added to water, will produce
solutions that are alkaline.
Alkaline Earth Metals
These elements are all found in the Earth’s crust, but not in the
elemental form as they are so reactive. Instead, they are widely
distributed in rock structures. Calcium is found in chalk,
limestone, and gypsum. Magnesium is the eighth most
abundant element in the Earth’s crust, and calcium is the fifth.
The metals of Group 2 are harder and denser than sodium and
potassium, and have higher melting points.
Three of these elements give characteristic colors when heated
in a flame:
Mg brilliant white Ca brick-red
Sr crimson Ba apple green
Fluorine-F, Chlorine-Cl, Bromine-Br, Iodine-I, Astatine-At
Metals in contact with halogens
will soon become a salt.
The total amount of astatine
present in the Earth's crust is
less than 1 oz
The halogens are the “greediest” of all the elements. They pull
electrons off of other elements. Fluorine is the strongest.
If they can’t pull the electron completely off they will at least
attract and keep it part of the time (electron sharing).
H2O + F2  HF + O2
•The elements are also grouped into four blocks with
different colors. These represent the different kinds of
electron orbitals (also called shapes or clouds).