The Atom
Chapter 11
Notes and Review
By: Mr. Steffen
John Dalton
J. J. Thompson
Dalton and Thompson started serious research on the atom.
Dalton suggested that elements combine in certain proportions
because they are made of single atoms. Thompson discovered that
there are small particles inside the atom. Thompson thought that
electrons were mixed throughout an atom, like the peanuts in
“chunky” peanut butter.
Ernest Rutherford
Rutherford conducted
experiments that
showed both
Thompson and Dalton
had parts of it right.
His experimentation
led him to conclude
that the atom was
mostly empty space
with a tiny part made
of highly dense
matter.
Rutherford proposed that the center of the atom was tiny,
dense and positively charged called the nucleus. The rays sent
at the gold foil would pass through the atom’s “empty” space
and bounce off of the densely packed nucleus.
So atoms have a densely packed nucleus made of protons
(+) and neutrons (=), and a spacious outer area that holds
electrons (-).
Neils Bohrs later added that the electrons moved around the
nucleus in certain paths, or energy levels. But electrons can
jump from path to path between levels, and each level can
only hold a certain number of electrons.
All atoms are different. Each had a different number of
protons, neutrons and electrons. These combine to create all
the matter around the Earth.
THE PERIODIC TABLE OF
ELEMENTS
Mendeleev started organizing the elements by
atomic mass. Moseley refined the chart by atomic
number. Moseley’s chart has been used ever since.
Atom – means not able to be divided; smallest particle an
element can be divided into and still be the same substance
Elements combine in certain proportions based on mass to form
compounds.
In 1803, scientists believed that atoms could not be broken down
or divided into smaller parts. However, Thomson later (1897)
found that they could be and further tests were done on atoms
by other scientists.
Scientists found protons, neutrons, and electrons.
Nucleus – positively charged center that includes protons and
neutrons; very, very dense
protons are positively charged and neutrons are neutral
A pinhead could be compared to a nucleus and a football stadium
as the rest of the atom.
Electron Clouds – areas inside of an atom where electrons are likely
to be found; the exact path cannot be predicted because they do not
travel in exact paths
Protons – positive charge; mass is very small at 1.7x10-24
or 1 atomic mass unit, or amu
*INSIDE the nucleus
Neutrons – neutral charge; a little larger than a proton but so
slight that it’s still considered to be 1 amu
*INSIDE the nucleus
Electrons – negatively charged
*mass is so small that they are not part of the total mass of
the atom
*takes more than 1800 electrons to equal the mass of 1
proton
*the number of protons are ALWAYS equal to number of
electrons in an element
*electrons travel on 4 levels OUTSIDE of the nucleus
Level 1 = 2 electrons
Level 3 = 18 electrons
Level 2 = 8 electrons
Level 4 = 32 electrons
Each level must be filled up before you can move to the next level.
Atoms have an overall neutral charge, but if the number of
protons and electrons changes, the atom becomes an ion,
which is a charged particle.
If an atom loses one or more electrons, it will have a positive
charge. If an atom gains 1 or more electrons, it will have a
negative charge because electrons have a negative charge.
The protons give an element its identity. For example, hydrogen
has 1 proton, so that’s its atomic number.
15
P
Phosphorus
31.0
15 is the atomic number, so you know
phosphorus has 15 protons. Since
protons are equal to electrons, there are
15 electrons. The mass is 31.0, which
is the # of protons and # neutrons
added together.
To find the number of neutrons, subtract the atomic # from
the mass #. 31-15=16 neutrons inside the nucleus.
Phosphorus – 15 protons, 16 neutrons, and 15 electrons
Level 1 = 2 electrons, Level 2 = 8 elec., Level 3 = 5 elec.
(Draw your Phosphorus atom here)
Isotope – atoms with the same # of protons but different #
of neutrons that share the same characteristics as the
original element.
Each element has a limited # of isotopes found in nature.
Some are unstable, which are called radioactive. They give
off energy as they fall apart in nature.
The Elements in all Their Glory
Each element is its own “thing”. They have some things in common with
other elements but each also has its own specific set of properties.