Download Inside an Atom - Mrs. Ericka Williams

Inside an Atom
Models of the Atom
pp. 510-520
1. What is an atom?
Chapter 17
Cannot be divided; for example, a string of beads can be cut
in half again and again until you have one
2. What is chemistry?
Study of matter
3. What happened in the Scientists began debating the existence of atoms once more;
eighteenth century?
they were learning about matter and how it changes; they
were putting substances together to form new substances and
taking substances apart to find out what they were made of;
they found that certain substances couldn’t be broken down
into simpler substances; they came to realize that all matter is
made of elements; for example, iron is an element made of
iron atoms so are carbon (carbon atoms), silver (silver atoms),
gold (gold atoms), oxygen (oxygen atoms), etc.
4. What is an element?
Is matter made of atoms of only one kind
5. Who is John Dalton? An English schoolteacher in the early 19th century who
P. 511
pictured the atom as a hard sphere that was the same
throughout (like a marble)
6. What did Dalton
He combined the idea of elements with the Greek theory of
propose?
the atom or ideas of the atom
1. Matter is made up of atoms.
2. Atoms cannot be divided into smaller pieces.
3. All the atoms of an element are exactly alike.
4. Different elements are made of different kinds of
atoms.
7. Who is William
In 1870, an English scientist by the name of William Crookes
Crookes? p. 511-512
tested Dalton’s theory by experimenting with a glass tube that
had almost all the air removed from it; the glass had two
pieces of metal called electrodes (piece of metal that can
conduct electricity) sealed inside; when the electrodes were
connected to a battery by wires, something flowed from the
negative electrode (cathode) to the positive electrode (anode)
8. What are cathode
Crookes hypothesized that the green glow in the tube was
rays (CRT)?
caused by rays or streams of particles; cathode ray tube gots it
name because the particles start at the cathode and traveled to
the anode; CRT’s used to be in a every TV and computer
monitor
9. Who is J.J.
In 1897, an English physicist by the name of J.J. Thompson
Thompson?
tries to disprove Crookes’ theory (Was the greenish glow a
light or was it a stream of charged particles?); he placed a
magnet beside the tube from Crookes’ experiment and you
can see that the beam is bent in the direction of the magnet;
light cannot be bent by a magnet so the beam cannot be a
light; so Thompson concluded that the beam must be made of
charged particles of matter that came from the cathode
10. What else did J.J.
Thompson discover?
11. Who is Ernest
Rutherford?
12. What are protons?
13. How did Rutherford
describe his new model?
14. What are neutrons?
15. After Rutherford’s
findings of the nucleus,
how did scientists revise
the atom model?
16. What particles are
in the nucleus of the
nuclear atom?
17. Further
Developments
18. What is the electron
cloud?
1. Electrons (negatively charged particles) (opposite
charges attract each other)
2. Revised Dalton’s atom model from the hard sphere
that was the same throughout (marble) to a sphere that
contains both positive and negative charge atoms
dispersed evenly p. 514
In 1906, he tried to disapprove Thompson’s atom model; his
experiment had alpha particles aimed at a thin sheet of gold
foil 400 nm (nanometers) thick; the foil was surrounded by a
fluorescent screen that gave a flash of light each time it was
hit by a charged particle; most particles passed right through
the foil or veered slightly from a straight line path but some
particles bounced right back p. 515; he proved that almost all
the mass of the atom and all of its positive charge are
crammed into an incredibly small region of space at the center
of the atom called the nucleus p. 516
Is a positively charged particle present in the nucleus of all
atoms
Most alpha particles could move through the foil with little or
nor interference because of the empty space that makes up
most of the atom; however, if an alpha particle made a direct
hit on the nucleus of a gold atom, which has 79 protons, the
alpha particle would be strongly repelled and bounce back
Would have the same mass as a proton and be electrically
neutral, has no charge
The nuclear atom has a tiny nucleus tightly packed with
positively charged protons and neutral neutrons; negatively
charged electrons occupy the space surrounding the nucleus;
the number of electrons in a neutral atom equals the number
of protons in the atom; for instance, if the ferris wheel in
London is 132 m, were the outer edge of the atom, the nucleus
would be about the size of a single letter o on a sheet of paper
Protons and neutrons

Electrons are constant, unpredictable motion and can’t
be described easily by an orbit
 Difficult to know the exact location of an electron at
any particular moment
 More likely to be close to the nucleus rather than
further away but they could be anywhere
Electrons traveling in a region surrounding the nucleus;
electrons are more likely to be close to the nucleus rather than
further away because they are attracted to the positive charges
of the protons; but they could be anywhere; there are no firm
boundaries
The Nucleus
pp. 521-529
19. What is the atomic
number of an element?
20. How are atoms of
an element identified?
21. What are isotopes?
22. What is the mass
number of an isotope?
23. What occurs in
radioactive decay?
24. What occurs in
transmutation?
25. Transmutation
(difficult)
26. How can you
determine when a
nucleus will decay?
27. What is carbon
dating?
The number of protons in the nucleus of an atom of that
element; for example, the smallest of the atoms is hydrogen
which has 1 proton in its nucleus, so hydrogen’s atomic
number is 1; another example, the heaviest naturally occurring
element is uranium which has 92 protons so its atomic mass is
92
They are identified by the number or protons because this
number never changes without changing the identity of the
element
Are atoms of the same element that have different numbers of
neutrons; for example, the three isotopes of carbon differ in
the number of neutrons in each nucleus such as Carbon 12,
Carbon 13, and Carbon 14 (p. 521 )
Is the number of neutrons plus protons or you can find the
number of neutrons by subtracting the atomic number from
the mass number (p. 522)
Nuclear particles and energy are released from the nucleus of
an atom; for example, Carbon 12 is the most stable isotope of
carbon (6 protons and 6 neutrons); some nuclei are unstable
because it has too many or too few neutrons such as uranium
and plutonium (heavier elements) which causes repulsion
build up, the nucleus must release a particle to become stable
When the particles that are ejected from a nucleus include
protons, the atomic number of the nucleus changes; when this
happens, one element into another through radioactive decay
Example: smoke detectors make use of radioactive decay;
this device contains americium – 241 (a muh RIH shee um),
which undergoes transmutation by ejecting energy and an
alpha particle (consists of 2 protons and 2 neutrons); together
the energy and particles are called radiation; the fast moving
alpha particles enable the air to conduct an electric current; as
long as the electric current is flowing, the smoke detector is
silent; the alarm is triggered when the flow of electric current
is interrupted by smoke entering the detector
Changed identity p. 523
Loss of beta particles (electrons) p. 524
It is impossible to determine when it will decay; radioactive
decay is random; for example, when watching popcorn, you
can’t predict which kernel will explode; this is why rate of
decay of a nucleus is measured by its half-life (of a
radioactive isotope is the amount of time it takes for half of a
sample of the element to decay)
Scientists have found the study of radioactive decay useful in
determining the age of artifacts and fossils; Carbon 14 is used
28. Why can’t carbon
dating be used to
determine the age of
rocks? What can be
used to determine the
age of rocks?
29. How and why do
scientists make synthetic
elements?
to determine the age of dead animals, plants, and organisms,
the amount of carbon 14 remains in constant balance with the
levels of the isotope in the atmosphere or ocean; this balance
occurs because living organisms take in and release carbon
carbon dating can only be used on things that have been alive;
however, geologists examine the decay of uranium; uranium
238 decays to lead 206 with a half life of 4.5 billion years; by
determining the amount of uranium to lead, they can
determine the age of a rock
A. By smashing atomic particles into a target element; the
absorbed particle converts the target element into
another element with a higher atomic number; this
new element is called synthetic element because it is
made by humans; these artificial transmutations have
created elements that do not exist in nature such as
elements with atomic numbers 93 to 112, 114, 116,
and 118.
B. Radioactive isotopes are used in hospitals and clinics
using specially designed equipment
C. Tracer elements are used to diagnose disease and to
study environmental conditions
D. Radioactive isotopes is introduced into living system
which if followed by a device that detects radiation
while it decays; these devices often present the results
of a photograph or a display on a screen; the isotopes
chosen for medical purposes have short half-lives,
which allows them to be used without the risk of
exposing living organisms to prolonged radiation
E. Medical uses of isotope to diagnose problems with
the thyroid, digestion problems, circulation and detect
cancer
F. Environmental uses to detect how a plant uses
phosphorus to grow and reproduce, how pesticides
moves through the ecosystem