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Theories Change …
•
The Atomic Theory of Matter states
that all matter is composed of small,
fast moving particles called atoms.
These atoms can join together to form
molecules.
• This theory is really thousands of
individual theories that provide
evidence for the whole theory.
HISTORY OF THE ATOM
460 BC
Democritus develops the idea of atoms
He pounded up materials in his pestle and
mortar until he had reduced them to
smaller and smaller particles which he
called
ATOMA
(greek for indivisible)
HISTORY OF THE ATOM
1808
John Dalton
Suggested that all matter was made
up of tiny spheres that were able to
bounce around with perfect elasticity
and called them
ATOMS
Dalton’s Atomic Theory (1808)
1. Elements are composed of extremely small
particles called atoms. All atoms of a given
element are identical. The atoms of one element
are different from the atoms of all other elements.
2. Compounds are composed of atoms of more
than one element.
3. Chemical reactions only involve the
rearrangement of atoms. Atoms are not created or
destroyed in chemical reactions.
2.1
16 X
+
8Y
8 X2Y
2.1
HISTORY OF THE ATOM
1898
Joseph John Thompson
Found that atoms could sometimes
eject a far smaller negative particle
which he called an
ELECTRON
HISTORY OF THE ATOM
1904
Thompson develops the idea that an atom was made up of
electrons scattered unevenly within an elastic sphere surrounded
by a soup of positive charge to balance the electron's charge
like raisins in a muffin.
Raisins in a Muffin
MODEL
2.2
HISTORY OF THE ATOM
1910
Ernest Rutherford
He fired Helium nuclei at a piece of gold foil
which was only a few atoms thick.
He found that although most of them passed
through. About 1 in 10,000 hit
HISTORY OF THE ATOM
helium nuclei
gold foil
helium nuclei
They found that while most of the helium nuclei passed
through the foil, a small number were deflected and, to their
surprise, some helium nuclei bounced straight back.
(1908 Nobel Prize in Chemistry)
1. atoms positive charge is concentrated in the nucleus
2. proton (p) has opposite (+) charge of electron
3. mass of p is 1840 x mass of e- (1.67 x 10-24 g)
2.2
Rutherford’s
Model of
the Atom
atomic radius ~ 100 pm = 1 x 10-10 m
nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m
2.2
HISTORY OF THE ATOM
Rutherford’s new evidence allowed him to propose a
more detailed model with a central nucleus.
He suggested that the positive charge was all in a
central nucleus. With this holding the electrons in
place by electrical attraction
However, this was not the end of the story.
HISTORY OF THE ATOM
1913
Niels Bohr
Studied under Rutherford at the
Victoria University in Manchester.
Bohr refined Rutherford's idea by
adding that the electrons were in
orbits. Rather like planets orbiting
the sun. With each orbit only able
to contain a set number of
electrons.
Bohr’s Atom
electrons in orbits
nucleus
HELIUM ATOM
Shell
proton
+
-
N
N
+
electron
What do these particles consist of?
-
neutron
All atoms are made up of just 3
basic sub-atomic particles:Name: Proton.
Mass: 1
Charge: +1
Name: Neutron. Mass: 1
Charge: 0
Name: Electron. Mass: 1/2000
Charge: -1
ATOMIC STRUCTURE
Notes: Atomic Theory
1. All atoms of a given element are identical. The
atoms of one element are different from the atoms of
all other elements.
2. Atoms are not created or destroyed in chemical
reactions, they are only rearrange.
3. Compounds are composed of atoms of more than
one element.
4. Subatomic particles are protons, neutrons and
electrons.
5. Protons and neutrons are together in the nucleus
Notes: Atomic Theory
6.
Electrons are in motion in orbits around the central
nucleus.
7.
Protons carry a positive electrical charge,
electrons carry a negative charge, and neutrons
carry no charge.
8.
Neutrons work to keep nuclei together.
9.
Most atoms are electrically neutral, meaning that
they have an equal number of protons and
electrons.
Notes: ATOMIC STRUCTURE
Symbol
He
Helium
Name
2
4
Atomic number
the number of protons in an atom
Atomic mass
the number of protons and
neutrons in an atom
Number of electrons = Number of protons
Isotopes are atoms with the same number of protons and different
number of neutrons.
Isotopes are atoms of the same
element (X) with different numbers of
neutrons in the nucleus
Mass Number
A
ZX
Atomic Number
1
1H
235
92
2
1H
U
Element Symbol
(D)
238
92
3
1H
(T)
U
2.3
2.3
Do You Understand Isotopes?
How many protons, neutrons, and electrons are in 146
C?
6 protons, 8 (14 - 6) neutrons, 6 electrons
How many protons, neutrons, and electrons are in 116
C?
6 protons, 5 (11 - 6) neutrons, 6 electrons
2.3
Let’s practice!!!
• Complete The Atoms Family - Atomic Math
Challenge.
• Play with gizmo:
www.explorelearning.com
Structure of the Atom
•
The Atomic Number of an atom = number of
protons in the nucleus.
•
The Atomic Mass of an atom = number of
Protons + Neutrons in the nucleus.
•
The number of Protons = Number of Electrons.
•
Electrons orbit the nucleus in shells.
•
Each shell can only carry a set number of electrons.
ATOMIC STRUCTURE
Electrons are arranged in Energy Levels or
Shells around the nucleus of an atom.
•
first shell
a maximum of 2 electrons
•
second shell
a maximum of 8 electrons
•
third shell
a maximum of 8 electrons
ATOMIC STRUCTURE
There are many ways to represent the atomic
structure of an element or compound.
One of them is:
1.
Electronic Configuration
ELECTRONIC CONFIGURATION
With electronic configuration elements are represented
numerically by the number of electrons in their shells
and number of shells. For example;
Nitrogen
2 in 1st shell
5 in
2nd
shell
configuration = 2 , 5
2
+
5 = 7
N
7
14
ELECTRONIC CONFIGURATION
Write the electronic configuration for the following
elements;
a)
Ca
20
b)
Na
40
2,8,8,2
d)
Cl
17
35
2,8,7
11
23
c)
2,8,1
e)
Si
14
28
2,8,4
O
8
16
2,6
f)
B
5
11
2,3
Mass
Number
The Simplest Atom
H
Name: Hydrogen
Atomic Symbol: H
1
1
Atomic
Number
Mass Number (Number of Protons + Neutrons) = 1
Atomic Number (Number of Protons) = 1
The Next Simplest Atom
Name: Helium
He
4
2
Atomic Symbol: He
The centre of an atom is called the NUCLEUS
A Helium atom has two protons and two neutrons in its nucleus
The Next Simplest Atom
Li
Name: Lithium
7
3
Atomic Symbol: Li
The orbit nearest the nucleus can only contain 2 electrons
so the third electron must be in a new orbit.
Electron Configuration: 2,1
The Next Simplest Atom
Name: Beryllium
Atomic Symbol: Be
This orbit
has room for 8 electrons
Electron Configuration: 2,2
Be
9
4
The Next Simplest Atom
B
Name: Boron
Atomic Symbol: B
5p 6n
Electron Configuration: 2,3
11
5
Valence Electrons
• All the elements in a group have similar
chemical properties as they have the same
number of outer electrons which are called
Valence electrons.
• For example: Group 1 Li and Na.
Noble Gas
Halogen
Group
Alkali Metal
Alkali Earth Metal
Period
2.4
Atoms and the Periodic Table.
We can classify (arrange) elements in different
ways:• naturally occurring/made by scientists
• solid/liquid/gas
• metal/non-metal
NOTES: The Periodic Table
1. The Russian scientist Dmitri Mendeleev published the
first periodic table because he noticed a pattern of
properties as he arrange elements by atomic mass.
2. Elements were rearranged by atomic number after the
proton was discovered.
3. The properties of an element can be predicted from its
location in the periodic table.
4. Each horizontal row of the table is called a period.
5. The elements in a column are called a group, or family.
6. The groups are numbered from Group 1 on the left to
Group 18 on the right.
Notes: The Periodic Table
7.
8.
9.
10.
11.
12.
13.
Stars consist of matter in the form of plasma, a gas-like
mixture .
Elements are created when the extreme high pressure
inside stars forces atomic nuclei to collide.
This process is called nuclear fusion.
Nuclear fusion combines smaller nuclei into larger
nuclei creating heavier elements.
Electrons are arranged in Energy Levels around the
nucleus of an atom.
They can hold 2 electrons in the first level, 8 in the
second and 8 in the third.
The outer electrons are called Valence electrons, and
each Group has the same number.
Metals
•
•
•
•
•
•
•
•
The physical properties of metals include:
Shininess
Malleability: can be hammered or rolled into flat sheets and
other shapes.
Ductility: can be pulled out, or drawn, into a long wire.
Conductivity: ability to transfer heat or electricity.
Magnetic: Attracted to magnets and can be made into
magnets.
Solids: Most are, at room temperature.
Corrosion: Some metals react with oxygen in the air, forming
rust.
Reactive: Combines with other elements with ease and
speed. Metals usually react by losing electrons to other
atoms. The reactivity of metals tends to decrease from left to
right across the periodic table.
Notes: THE PERIODIC TABLE
METALS
NONMETALS
METALLOIDS
A substance or mixture
that has a luster or
shine, is generally a
good conductor of heat
& electricity, & is
malleable & ductile.
They can corrode and
can become magnetic.
An element that does
not exhibit the
characteristics of a
metal; they are
generally solids or
gases and are usually
hard, brittle substances.
An element having both
metallic and
nonmetallic properties.
They are usually good
semiconductors
Except for mercury, the
metallic elements are
solids at room
temperature (~20° C)
Bromine is the only
liquid nonmetal.
Hydrogen
• Hydrogen belongs to a
family of its own.
• Hydrogen is a diatomic,
reactive gas.
• Hydrogen was involved in
the explosion of the
Hindenberg.
• Hydrogen is promising as
an alternative fuel source
for automobiles
Alkali Metals
• 1st column on the
periodic table (Group
1) not including
hydrogen.
• Very reactive metals,
always combined with
something else in
nature (like in salt).
• Soft enough to cut
with a butter knife
Alkaline Earth Metals
• Second column on
the periodic table.
(Group 2)
• Reactive metals that
are always combined
with nonmetals in
nature.
• Several of these
elements are
important mineral
nutrients (such as Mg
and Ca
Transition Metals
• Elements in groups 312
• Less reactive harder
metals
• Includes metals used
in jewelry and
construction.
• Metals used “as
metal.”
Boron Family
• Elements in group 13
• Aluminum metal was
once rare and
expensive, not a
“disposable metal.”
Carbon Family
• Elements in group
14
• Contains elements
important to life and
computers.
• Carbon is the basis
for an entire branch
of chemistry.
• Silicon and
Germanium are
important
semiconductors.
Nitrogen Family
• Elements in group 15
• Nitrogen makes up over
¾ of the atmosphere.
• Nitrogen and
phosphorus are both
important in living
things.
• Most of the world’s
nitrogen is not available
to living things.
• The red stuff on the tip
of matches is
phosphorus.
Oxygen Family or Chalcogens
• Elements in group 16
• Oxygen is necessary
for respiration.
• Many things that
stink, contain sulfur
(rotten eggs, garlic,
skunks,etc.)
Halogens
• Elements in group 17
• Very reactive, volatile,
diatomic, nonmetals
• Always found
combined with other
element in nature .
• Used as disinfectants
and to strengthen
teeth.
• Salt forming.
The Noble Gases
The Noble Gases
• Elements in group 18
• VERY unreactive,
monatomic gases
• Used in lighted “neon”
signs
• Used in blimps to fix
the Hindenberg
problem.
• Have a full valence
shell.
Notes:The Periodic Table (12 parts)
Hydrogen 1ve
Alkali Metals 1ve
Alkaline Earth Metals 2ve
Boron Family 3ve
Transition Metals
Carbon Family 4ve
Nitrogen Family 5ve
Oxygen Family 6ve
Halogens Family 7ve
Lanthanides
Noble Gases Family 8ve
Actinides
Transition Metals,
Lanthanides and
Actinides have different
number of valence
electrons.
Notes: The Periodic Table
14. Elements that follow uranium are made when
nuclear particles are forced to crash into one
another.
15. Elements with atomic numbers above 92 are
synthetic and are made in nuclear reactors or
powerful machines called particle
accelerators .
16. Semiconductors are substances that under
some conditions can carry electricity, and
under other conditions cannot carry
electricity.
Links
Webelements.com
Interactive Periodic Table
The Visual Elements Periodic Table
Chemical Elements
Los Alamos National Laboratory
Additional Physics Tutorials
Notes:
1.
2.
3.
4.
5.
Radioactivity
In a process called radioactive decay, the atomic nuclei of
unstable isotopes release fast-moving particles and
energy.
In 1896, the French scientist Henri Becquerel discovered
radioactive decay quite by accident while studying a
mineral containing uranium.
Becquerel presented his findings to Marie Curie and her
husband Pierre .The Curies concluded that a reaction
was taking place with the uranium nuclei.
Radioactivity is the name that Marie gave to this
spontaneous emission of radiation by an unstable atomic
nucleus.
Natural radioactive decay can produce alpha particles,
beta particles, and gamma rays.
Notes:
6.
7.
8.
9.
10.
11.
12.
Radioactivity
The particles and energy produced during radioactive decay are
forms of nuclear radiation.
An alpha particle consists of two protons and two neutrons and is
positively charged. It is the same as a helium nucleus. Alpha
radiation can cause an injury much like a bad burn.
After alpha radiation the atomic number is decreased by 2 and the
atomic mass by 4.
A beta particle is a neutron that changes into a proton and a
negative beta particle. Beta particles can travel into the body and
cause cell damage.
After beta radiation the atomic number increases by 1 and the
atomic mass decreases by 1.
Alpha and beta decay are almost always accompanied by gamma
radiation which is detectable.
Gamma radiation is high-energy waves. Gamma rays can pass
right through the human body, causing severe cell damage.
Notes:
Radioactivity
13. Uses of radioactive decay include tracing the steps of
chemical reactions and industrial processes, and
diagnosing and treating disease.
14. Tracers are radioactive isotopes that can be followed
through the steps of a chemical reaction or an
industrial process.
15. In addition, the radiation given off by certain
radioactive isotopes can be used to destroy unhealthy
cells in the body, such as those in cancer tumors.
16. Nuclear Decay Gizmo
Notes:
Half-life
1. Half – life
2. As a radioactive element within a rock or object
decays, it changes into another element.
3. Therefore, the composition of the object
changes slowly over time. The amount of the
radioactive element decreases. But the amount
of the new element increases.
4. The half-life of a radioactive element is the
time it takes for half of the radioactive atoms to
decay.
Notes:
Half-life
5. Scientists often use potassium-40 to date
rocks. This form of potassium decays to form
the stable element argon-40 and has a half-life
of 1.3 billion years. The long half-life of
potassium-40 makes it useful in dating the
most ancient rocks.
6. Carbon-14 is useful in dating materials from
plants and animals that lived as far back as
50,000 years ago. Because carbon-14 has a
half-life of only 5,730 years, it can’t be used to
date more ancient fossils or rocks.
Notes:
Half-life
• Percentage What percentage of a radioactive element
will be left after 3 half-lives? First, multiply ½ three times
to determine what fraction of the element will remain.
• You can convert this fraction to a percentage by setting
up a proportion:
• To find the value of d, begin by cross multiplying, as for
any proportion:
• Practice Problems What percentage of a radioactive
element will remain after 5 half-lives?
Links to radioactivity
• BrainPop Movie
• Nuclear Decay Gizmo
• Uses of Radiactivity