Download Atomic Structure

Atomic Structure Review
AC Physical Science
2008
Atom, Molecule, or
Compound ??
• Atoms - smallest particle of an element
• Element – cannot be broken down by any
means possible
• Molecule – 2 or more atoms that are
bonded together. For example O2 and H2O.
• Compounds – substance made of 2 or
more elements. For example: H2O
• ALL compounds are also molecules, BUT
all molecules ARE NOT compounds…
WHY??
Elements…
• Cannot be separated into simpler
substances by any chemical or
physical means.
• Pure Substances are substances where
there is only one type of particle – for
example pure oxygen.
• Elements have their own unique
properties, but can share
characteristics.
Classifying Elements
• Classified by their properties…
• Categories are defined as metals,
nonmetals, and metalloids.
• Samples of metals = Pb, Cu, Sn
• Samples of nonmetals = S, Ne, I
• Sample of metalloids = Si, B, Sb
Molecules
• 2 or more atoms that are combined
together
• Example = O2
Compounds
• A Compound is a pure substance
composed of 2 or more elements that
are chemically combined.
• Examples: CO2
Mixtures
• Combination of 2 or more substances
that are not chemically combined
• Solutions – mixture that appears to be
a single substance – composed of 2 or
more substances that are evenly
distributed among each other.
• Solute – substance that is dissolved
• Solvent – substance in which the solute
is dissolved in
Mixtures continued…
• Concentration – measure of the amount of
solute dissolved in a solvent
• Solubility – solutes ability to dissolve in the
solvent at a certain temperature
• Suspension – mixture in which particles of a
material are dispersed throughout a liquid or
gas (example Italian Salad Dressing)
• Colloid – mixture consisting of tiny particles
that are dispersed throughout, but are not
heavy enough to settle out (Example = jello
or milk)
Atoms..
• Atom = the smallest particle an element
can be divided into and still be the
same substance.
• Atom is from the Greek word atomos,
meaning “not able to be divided”.
Dalton’s Atomic Theory
• John Dalton, a British chemist
published his theory in 1803.
• His theory states the following ideas:
– All substances are made of atoms. Atoms
are small particles that cannot be created,
divided, or destroyed.
– Atoms of the same element are exactly
alike, and atoms of different elements are
different.
– Atoms join with other atoms to make now
substances.
Not quite correct…
• 1897, J.J. Thomson showed that there
was a mistake in Dalton’s theory.
• He discovered that there are smaller
particles inside the atom.
• Which means that the atom can be
divided into even smaller parts.
• Thomson discovered negatively
charged particles that are called
electrons.
Rutherford’s Atomic
“Shooting Gallery”
• In 1909, Ernest Rutherford tested Thomson’s
Theory.
• He aimed a beam of small positively charged
particles at a thin sheet of gold foil.
• In 1911, Rutherford revised the atomic
theory. He made a new model.
• He proposed that the center of an atom
is tiny, extremely dense, and positively
charged part called the nucleus.
• Because like charges repel, a particle
that headed straight for a nucleus
would be pushed almost straight back
and in the direction in which it came.
Bohr’s Electron Level
• In 1913, Niels Bohr, worked with Rutherford,
And studied that way that atoms react to
light.
• The results led him to propose that electrons
move around the nucleus in certain paths or
energy levels.
• Bohr’s model was a valuable tool in
predicting some atomic behavior, but the
atomic theory still had room for
improvement.
The Modern Atomic Theory
• Erwin Schrödinger and Werner
Heisenberg work and further explained
that nature of electrons in an atom.
• The determined that the exact path of an
electron cannot be predicted.
• According to the current theory, there are
regions inside the atom where electrons
are likely to be found.
• These regions are called electron clouds.
Electron Clouds…
• Use the formula 2(N2) to determine
how many electrons fit in each
cloud…
Practice, Practice…
Parts of an Atom
• Nucleus: the small dense positively
charged center of the atom.
– This contains most of the atom’s mass.
• Protons: are positively charged particles
in the nucleus of an atom
• Neutrons: are particles in the nucleus that
have no charge.
• Electrons: negatively charged particles
found in the electron clouds outside the
nucleus.
Subatomic Particles…
•
•
•
•
Protons are positive +
Neutrons are neutral
Electrons are negative –
Protons and neutrons are in the
center of the nucleus
• Electrons are situated in electron
clouds spinning around the nucleus
Things to remember…
• Atomic Number = the number of
protons and electrons
• The difference between the atomic
number and the atomic mass = the
number of neutrons
The Nucleus
• Protons: are positively charged
particles in the nucleus of an atom
• The SI unit used to express the masses
of particles in atoms is the:
atomic mass unit (amu)
– Each proton has a mass of about 1amu
• Neutrons: are particles in the nucleus
that have no charge.
Outside the Nucleus
• Electrons: negatively charged particles
found in the electron clouds outside the
nucleus.
• Compared with protons and neutrons,
electrons are very small in mass.
• The charges of protons and electrons are
opposite, but equal, so they cancel each
other out.
• Because an atom has no overall charge, it is
neutral.
• What happens if the numbers of the
electrons and protons are not equal?...
Well…Ions…
• The atom becomes a charged particle
called an ion.
• An ION is an atom or group of atoms
that carry an electric charge.
• So…if an atom has more protons it
is???
• If there are more electrons??
• This is how weather patterns are
created…
Isotopes
• An atom that has the same number or
protons (or the same atomic number)
as other atoms of the same element do
but that has a different number of
neutrons (and thus a different atomic
mass).
• You can tell Isotopes apart by the mass
number which is the sum of the numbers
of protons and neutrons in the nucleus of
an atom. Example of an Isotope =
Carbon-14 used to date rocks…
How do I find Neutrons again?
• The difference between the atomic
number and the atomic mass = the
number of neutrons