Download Atom - Perry Local Schools

Bellwork: What information can be used for identifying where you live? How are YOU identified?
Power of the mind and intellectual thought were the
primary avenues to the truth.
Curiosity sparked the interest of scholarly thinkers known
as philosophers who considered many of life's mysteries.
As the speculated about the nature of matter, many
philosophers formed explanations based on their
own life experiences.
1
Democritus
-proposed the IDEA that matter was not infinitely
divisible they were solid, homogenous, could not be
created or destroyed or further divided
-matter was made up of tiny individual particles called
atomos (we derive our English word, atom) which move
through empty space
-different kinds of atoms have different shapes and
sizes
-size, shape, and movement of atoms determine the
properties of matter
Aristotle
-rejected the idea of atoms (denied their
existence), he didn't believe empty space
could exist.
-matter is made of earth, fire, air, and
water
-because he was very influential people
rejected Democritus
-No one challenged him for 2,000+ years!
2
Dalton
-could actually do experiments
-Created Dalton's atomic theory
*matter is composed of extremely small particles called
atoms
*atoms are indivisible and indestructible
*atoms of a given element are identical in
size, mass, and chemical properties
*atoms of a specific element are different
from those of another element
*different atoms combine in simple wholenumber ratios to form compounds
*in a chemical reaction, atoms are separated, combined, or
rearranged.
Dalton's theory easily explains that conservation of mass
in chemical reactions is the result of separation,
combination, or rearrangement of atoms (not created,
destroyed, or divided)
Dalton's theory has been revised due to new information
being discovered:
-atoms are divisible
-not all atoms of an element have the same properties
-atoms of the same element can have slightly
different masses
3
Atom-smallest particle of an element that retains the
properties of the element.
-idea of its size: world population = 6.5x109 in 2006.
The penny has 2.9x1022 atoms. (5 trillion times world
population!)
-They can be seen! You have to use a scanning
tunneling microscope (STM) to see individual atoms.
Once people were convinced that the atom existed -it led to
more questions being asked just like all good experiments.
-Scientists began to make connections between matter
and electric charge.
-Some wondered how electricity might behave in the
absence of matter.
-Used the newly invented vacuum pump to pass electricity
though glass tubes from which most of the air had been
removed.
-tubes are called cathode ray tubes. (positive end is
called anode, negative end is called cathode)
4
Crooks
-saw a spark of green light when the electricity struck
zinc sulfide coating in the tube (some sort of radiation
was produced)
-Cathode ray was the name given to this spark of light,
this eventually led to the invention of the tv.
-Conclusions: streams of charged particles were
passing through the tube, they carried a negative charge.
-later negatively charged particles were called
electrons
J.J. Thomson
-measured effects of both magnetic and
electric fields on a cathode ray after
comparing his findings with charge to mass
ratios
-he concluded that the mass of the charged particle was much
less than the hydrogen atom, the lightest known atom.
-This meant that there were particles smaller than an
atom. -Dalton was incorrect!
-He had identified the first subatomic particle -the electron
-received the Nobel prize in 1906 for its discovery
5
Millikan
-did oil drop experiment and determined the charge
of an electron.
-His setup was so good that it is within 1% of the
current accepted value!
-then knowing the charge and the known charge-tomass ratios, he calculated the mass of an electron
Two major questions were then asked: If electrons mass is
so small, what accounts for the rest of the mass in an
atom? & If an electron is negative, how is it that all
matter is neutral?
J.J. Thomson proposed a model of the atom known as the
plum pudding model
-said there was positive charge throughout and that
negative electrons sat with in
-his model didn't last long.
6
Rutherford
-studied how positively charged particles interacted
with solid matter.
-conducted an experiment to see if alpha
particles would be deflected as they passed
through a thin piece of gold foil
-Hypothesis: it wouldn't alter the path of alpha
particles and that they would see slight altered
paths when collisions happened with an electron.
Results: most past right through with no deflection,
some were deflected at large angles and some came
straight back.
-Kind of like firing a large artillery shell at a sheet
of paper and the shell coming back at the cannon!
7
Concluded:
-Plum pudding model was wrong,
-atom is mostly empty space through which electrons
move
-most of atom's positive charge and almost all of its
mass were contained in a tiny dense region in the
center of the atom-called the nucleus
-negative particles are held within the atom by their
attraction to positive nucleus
Nucleus is very dense. IF it was the size of the dot on an exclamation point mass would be as much as 70 automobiles! If its diameter was 2 football fields, nucleus would be the size of a nickel.
­Neutral Nature of Matter: the positive charge in the nucleus is balanced out by the negative electrons ­but didn't account for atomic mass.
Bellwork: Complete the worksheet (front
and back) that you picked up for 4.1 and
4.2 as a way of reviewing all of the
history from yesterday.
8
Proton­ carries an equal but opposite charge of an electron.
­Rutherford discovered it
Chadwick ­discovered that nucleus also has neutrons (also won Nobel prize)
Neutron mass = mass of proton
Neutrons have NO CHARGE
Summary:
­All atoms are made up of 3 fundamental subatomic particles: protons, neutrons, and electrons
­Atoms are spherically shaped, small, dense nucleus of positive charge surrounded by negative charge (1 or more)
­Most of an atom is fast­moving electrons traveling through empty space that surrounds the nucleus.
­electrons are held by their attraction to positive charge in the nucleus
­nucleus contains protons and neutrons and they make up 99.97% of the mass of an atom.
­atom is neutral: #protons = # electrons
­Subatomic particles are made up of quarks
9
Homework: 4,6,7
4. Explain how Dalton's theory of the atom and the conservation of
mass are related.
Dalton explained that atoms are neither created nor destroyed in
chemical reactions, only rearranged.
6. Design a concept map that compares and contrasts the atomic
ideas proposed by Democritus and Dalton.
See next page.
7. Describe the structure of a typical atom. Identify where each
subatomic particle is located.
A typical atom consists of a central, small, dense nucleus containing
protons and neutrons. The nucleus is surrounded by a cloud of
negatively charged electrons.
matter composed
of extremely
small particles
called atoms
all atoms of a given
element are
identical but differ
from the atoms of
other elements
Democritus
matter is composed of
empty space through
which atoms move
atoms could not
be created,
divided, or
destroyed
Dalton
different kinds of
atoms come in
different sizes and
shapes
different atoms
combine in simple
whole-number ratios
to form compounds
differing
properties of
atoms are due to
the size, shape,
and movement of
the atoms
10
Henry Moseley
­discovered atoms of each element contain a unique positive charge in the nuclei
­number of protons in an atom identifies the atom
­we call this atomic number
­The periodic table is organized left to right and top to bottom by increasing atomic number.
­All atoms are neutral; therefore, #p+ = #e­
Using what you know and have learned...try completing the table. You will want to use the periodic table in the back of your book, or the one on the back wall :)
Element
Atomic Number
Protons
Electrons
19
35
Ne
10
11
ANSWERS
Element
Atomic Number
Protons
Electrons
K
19
19
19
Br
35
35
35
Ne
10
10
35
Classwork pg 116: 12­15
12. How many protons and electrons are in each atom?
b. magnesium
a. radon
a. 86p, 86e
b. 12p, 12e
13. An atom of an element contains 66 electrons.
dysprosium
Which element is it?
14. An atom of an element contains 14 protons.
silicon
Which element is it?
15. Do the atoms shown in the figure have the same atomic number?
yes, there are nine
12
­Number of neutrons can be different
­Atoms with the same number of protons but different numbers of neutrons are called isotopes.
­atoms with more neutrons have more mass
­Isotopes of same element all have the same chemical behavior.
­the number of electrons is the only thing that chemical behavior is dependent upon.
­Each isotope of an element is identified with a number called mass number.
Mass # = atomic number + neutrons
­Example: Copper­63, Copper­65
*remember: atomic number (protons) doesn't change!
­In nature elements are found as mixtures of isotopes. How much each isotope occurs in any given substance is constant
Due to mass of p+, no, and e­ being so small chemist developed a method for measuring the mass of an atom relative to mass of a specific atomic standard.
­The standard is Carbon­12
­Carbon has exactly 12 amu so 1 amu = 1/12 the mass of a carbon­12 atom = almost the mass of one proton.
Atomic mass of an element is a weighted average of the isotopes of that element.
­Sometimes you can gain an understanding of which isotope may be more common if the amu is close to a whole number it indicates that isotope is more common (not always)
13
Homework: Practice Problems 18,19, 21,23, 24
18. Boron has two naturally occuring isotopes: boron-10 (19.8%
abundant, mass 10.013amu) and boron-11 (80.2% abundant, mass
11.009 amu) Calculate the atomic mass of boron. 10.81amu
19. Nitrogen has two naturally occurring isotopes, N-14 and N-15.
Its atomic mass is 14.007. Which isotope is more abundant?
Explain your answer.
N-14 is most likely more abundant because the atomic mass is
closer to 14 than 15.
21. Which subatomic particle identifies an atom as that of a
particular element? the proton
23. Copper has two isotopes: Cu-63 (abundance 69.2%, mass =
62.930 amu). Cu-65 (abundance 30.8%, mass = 64.928 amu).
Calculate the atomic mass of copper. 63.5amu
24. Three magnesium isotopes have atomic masses and relative
abundances of 23.985amu (78.99%), 24.986% (10.00%), and
25.982 (11.01%). Calculate the atomic mass of magnesium.
24.31amu
14
Bellwork: Refresh your memory, what
is a chemical reaction?
A chemical reaction is the change of
one or more substances into new
substances -this only involves the
electrons.
Nuclear Reaction- can change one element into
another element by creating a change in the
nucleus of the atom.
-We realized its existence in a process called
radioactivity where radiation was
spontaneously emitted.
Radiation- rays or particles emitted by
radioactive material.
Why do they emit radiation? -their nuclei are
unstable
-Unstable nuclei lose energy by emitting
radiation in a spontaneous process called
radioactive decay.
-the primary factor in determining an atom's
stability is its ratio of neutrons to protons
15
3 types of radiation-based on their electrical charge.
alpha particles (2p+, 2no) = 2+ charge
-Ernest Rutherford, an English scientist, discovered alpha
particles in 1899 while working with uranium.
-occur naturally in the environment in soils, rocks, and water
Uses of alpha particles:
*Radium-226 may be used to treat cancer, by inserting tiny
amounts of radium into the tumorous mass.
*Polonium-210 serves as a static eliminator in paper mills
and other industries. The alpha particles, due to their
positive charge, attract loose electrons, thus reducing
static charge.
*Some smoke detectors use the alpha emissions from
americium-241 to help create an electrical current.
beta particles (e­) = 1­ charge
­Henri Becquerel is credited with the discovery of beta particles. In 1900, he showed that beta particles were identical to electrons, which had recently been discovered by J. J. Thompson.
­energy can break chemical bonds and form ions.
­ used in medical diagnosis, imaging, and treatment
­harmful to cells and the environment
­people who have taken radioactive iodine will emit beta particles. ­Radioactive iodine may enter the environment during a nuclear reactor accident and find its way into the food chain.
16
Gamma Rays - no mass, no charge, usually accompany
alpha or beta radiation, and they account for most energy
lost during decay.
-Henri Becquerel discovered them, shortly after x- rays
were discovered. He said uranium emitted similar invisible
light energy.
-Gamma photons have about 10,000 times as much
energy as the photons in the visible range of the
electromagnetic spectrum.
-They can pass through many kinds of materials,
including human tissue...lead is often used to help
shield us against them.
What's the difference between x-rays and gamma rays?
-Gamma rays originate in the nucleus. X-rays
originate in the electron fields surrounding the
nucleus or are machine-produced.
17