Download Chemistry Internal Structure Notes When thinking about atomic

Chemistry
Internal Structure
Notes
When thinking about atomic theory and the nature of matter, we must keep in mind this important question: What is the
experimental evidence that justifies our ideas about internal structure? Use the table below for guidance over the
question of evidence.
Note: The items in the “evidence” column and “resources” column just represent a few tiny snapshots in a huge field of
study.
Concept
Matter is constructed of tiny particles that we
call atoms, molecules, and ions.
Evidence
The results of X-ray crystallography indicate that
solids possess an orderly internal structure made
of points that lie on a grid or lattice. These points
are mathematically related to the positions of the
particles (atoms or ions) that make up the solid.
Atomic force microscopy provides relatively new
tool for imaging individual atoms and ions directly.
Atoms consist of a tiny, dense, positively
charged nucleus surround by a cloud of very
light and negatively charged electrons.
The nucleus of an atom contains individual
positive charges named protons. The number
of protons in the nuclei of atoms determines
the unique identity of each element in the
periodic table. The number of protons is
known as the atomic number of the element.
Resources
https://www.youtube.com/watc
h?v=2w5-AOUuqNA
https://en.wikipedia.org/wiki/Xray_crystallography#/media/Fil
e:Xray_diffraction_pattern_3clpro.j
pg
Rutherford’s gold foil experiment is regarded as
the key result that ushered in the nucleuscentered model of the atom. Huge amounts of
subsequent evidence corroborate the nucleuscentered model.
https://www.youtube.com/watc
h?v=5pZj0u_XMbc
In 1913 Henry Moseley discovered that different
elements can be made to emit different
frequencies of X-rays, and that these frequencies
vary as a function of a whole number that we now
call the atomic number – the number of protons in
the nucleus. (Tragically, Moseley died at the age
of 27 in the Battle of Gallipoli in WWI.)
http://www.rsc.org/Education/T
eachers/Resources/periodicta
ble/pre16/order/atomicnumber.
htm
Click the link in the
www.rsc.org article to view a
graph of Moseley’s data.
over
https://www.youtube.com/watc
h?v=XBqHkraf8iE
Textbook
(Blue)
The nucleus of an atom contains electrically
neutral neutrons in addition to protons.
Neutrons possess a mass that’s essentially
equal to the proton’s mass.
After Rutherford’s experiment, researchers
(among them Rutherford and his associates)
realized that the nucleus must contain more mass
than the mass from the protons alone, since the
mass numbers for the elements had been known
long before the atomic numbers. Chadwick, who
had worked with Rutherford, is credited with
directly discovering the neutron in 1932.
http://wwwoutreach.phy.cam.ac.uk/camp
hy/neutron/neutron2_1.htm
Many elements don’t exist as atoms – they
exist as electrically charged particles named
ions.
We collected this evidence ourselves by using a
9V battery and Al foil electrodes. Table salt
(sodium chloride) is electrically neutral. Dissolve
NaCl in water and the solution becomes
electrically conductive. Molten sodium chloride is
similarly conductive. The conductivity of these
materials indicates that solid sodium chloride is
made of positively and negatively charged
particles named ions
http://whatis.techtarget.com/de
finition/ion
Ions are atoms that contain an excess or a
deficit of electrons. The sodium ion, Na+,
contains 11 protons and 10 electrons.
We infer that variations in electron numbers, not
proton numbers, are responsible for ions because
changing the number of protons changes the
identity of the element. A sodium atom with a
missing electron is a sodium cation, Na+. A
sodium atom with the deficit of a proton isn’t
sodium – it’s neon.
https://en.wikipedia.org/wiki/Io
n
The electric charges on one-atom ions form
patterns according to the positions of the
corresponding elements in the periodic table.
All the group 1 metals exist as +1 ions. All the
group 7 nonmetals exist as -1 ions.
The chemical formulas of electrolytes reveal the
electric charges on the constituent ions. On the
left and right side of the periodic table, we can see
that the charges on one-atom ions align with the
elements’ positions on the periodic table.
http://terpconnect.umd.edu/~w
breslyn/chemistry/naming/findi
ngioniccharge.html
over