Download Chapter 14: Inside the Atom

Chapter 14: Inside the
Atom
Pages 404 - 423
First Thoughts of the Atom
• “Cannot be divided”
• Keep dividing matter until
only one particle remains
• Chemistry – study of
matter
A Model of the Atom
• Element – matter made of
atoms of only one kind
• Dalton’s Concept –
– Matter is made up of atoms
– Atoms cannot be divided into
smaller pieces
– All atoms of an element are
exactly alike
– Different elements are made of
different kinds of atoms
*Thought was like tiny marble
• William Crookes Experiment
– Showed particles were traveling
in a straight line from the
negative electrode to the
positive
– CRT – once used in TV’s and
computer monitors
Discovering Charged Particles
• J.J. Thomsom – used magnet
on CRT and beam was bent
towards it
• Proved that this was not light,
but made of charged particles
of matter
• Electrons – negatively
charged particles
• Particles smaller than atoms
do exist
• Atomic Model:
– Sphere of positive charge
– Negatively charged electrons
spread evenly throughout
positive charge
– Positive=Negative
– Atom is neutral
– Later discovered not all atoms are
neutral
– More positive electrons = + atom
– More negative electrons = - atom
Questions
1. What does the word atom mean?
2. What 4 concepts did Dalton
propose about atoms?
3. What did William Crookes
experiment show?
4. How did Thomson prove particles
were in the CRT and not light?
5. What type of particle did
Thomson discover?
6. Describe what an atom looks like.
7. How do we know if an atom is
neutral or has a positive or
negative charge?
Rutherford’s Experiments
• Tested Thomson’s model
to see if correct
• Alpha particles
bombarded gold foil
• Most passed through or
veered slightly, but some
bounced right back!
A Model with a Nucleus
• Hypothesized that almost all
mass of an atom and all
positive charge is crammed
into one small space in the
center called the nucleus
• Proton – positively charged
particle in the nucleus of an
atom
• The rest of the atom is empty
space occupied by almost
massless electrons
• Neutron:
– Same mass as a proton
– Neutral charge
– Located in nucleus
– Neutral atom has equal
number of protons and
electrons
electron
neutron
proton
Further Developments
• Electrons – in constant,
unpredictable motion,
impossible to know precise
location of an electron
• Electrons act as waves
• Electron Cloud – region
surrounding nucleus where
electrons travel
• Electron energy levels – Niels
Bohr
Questions
1. What did Rutherford
discover about the atom
from his experiment?
2. What is a proton?
3. What is a neutron?
4. How does an atom get a
neutral charge?
5. Describe the behavior of an
electron in an atom.
6. Where are electrons located
in an atom?
Chapter 14 Section 2:
The Nucleus
Pages 415 - 423
Identifying Numbers
• Atoms of different elements contain
different #s of protons
• Atomic number is the number of protons
in the nucleus of an atom of that element.
• Smallest: Hydrogen has 1 proton, atomic
# is 1
• Heaviest: Uranium has 92 protons,
atomic # is 92
• Elements are identified by their atomic #
(doesn’t change for an element)
Number of Neutrons
• Atoms can have a varying # of
neutrons in the nucleus.
• Isotopes are atoms of the same
element that have different #s of
neutrons.
• Mass #: the # of neutrons +
protons.
• Strong nuclear force holds
protons together that are tightly
packed in the nucleus.
Radioactive Decay
• unstable nuclei have too many or too
few neutrons.
• Radioactive decay: nucleus releases
particles to become stable
• If protons are released the element is
changed
• Transmutation is the changing of an
element due to radioactive decay.
• Alpha particle = 2 protons and 2
neutrons.
• Beta particle = high energy electron
that comes from the nucleus, not from
the electron cloud.
• Neutron becomes unstable and splits
into a proton (+) and an electron (-)
• Electron (-) is given off
• Nucleus now has 1 more proton (+),
and is a new element.
Questions
1. Define atomic number.
2. What are the smallest and heaviest
elements?
3. Define Isotope.
4. What is mass number?
5. What is radioactive decay?
6. How could an element be changed during
radioactive decay?
7. What is an alpha particle?
8. How does a beta particle being released
affect an element?
Rate of Decay
• Half-life of a radioactive
isotope is the amount of
time it takes for half of a
sample of the element to
decay.
• Not affected by weather,
pressure,
magnetic/electric fields,
or chemical reactions.
Carbon Dating
• Carbon 14 is used to find the age of
once living things (fossils, dead
animals, plants and humans.)
• Half-life of Carbon14 is 5,730 years
• Compare amounts of Carbon14 in old
items with the amount of Carbon14
new items to determine age.
• Uraium 238 is used to date non living
things (rocks)
Making Synthetic Elements
• Scientists create new elements by
smashing atomic particles into a
target element.
• Isotope iodine131 used to diagnose
thyroid problems.
• Radioisotopes can help discover
how pesticides move throughout an
ecosystem
Questions
1.
2.
3.
4.
5.
Define half-life.
What is Carbon14 used to date?
What is the half-life of Carbon14?
What is Uranium238 used to date?
How do scientists create new
elements?
6. How are synthetic elements useful?