Download Atoms

Bellwork 10/19/15
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P. Sci.
Unit 8
Chapter 4
Atoms
Atomic Structure – timeline
• Ancient Greece - Democritus
proposed the atom – a tiny solid
particle that could not be
subdivided.
• 1904 – J.J. Thomson –
discovered that atoms contained
small, negatively charged
particles called electrons.
• 1911 – Ernest Rutherford –
proposed that the atom had two
parts – the nucleus in the center
(most of the mass) surrounded
by the electrons.
• 1913 – Niels Bohr –
hypothesized that
electrons traveled in fixed
orbits around the atom’s nucleus.
• 1913 – James Chadwick –
concluded that the nucleus
contained positive protons and
neutral neutrons.
• 1926 – Erwin Schrodinger –
developed the quantum
mechanical model – which is
based on the wavelike properties
of the electron. (not a particle –
leads to quantum physics)
• 1927 – Werner Heisenberg
– (the Heisenberg
uncertainty Principle)
described that it is
impossible to know
precisely both an
electron’s position and
path at a given time. Led to
the electron cloud theory.
electron
neutron
proton
Atoms
• The smallest particle that has the
properties of an element.
Dalton’s Atomic Theory
• Every element is made of tiny,
unique, particles called atoms that
cannot be subdivided.
• Atoms of the same element are
exactly alike.
• Atoms of different elements can
join to form molecules or
compunds
Parts of an Atom
• Nucleus – small, dense center of
an atom made up of 2
subatomic particles that are
identical in size and mass.
–Protons – have a
positive charge
–Neutrons – have no charge
Parts of an Atom cont.
• Electrons – are tiny subatomic
particles that have very little mass
that moves around the outside of
the nucleus. These particles are
negatively charged and form a
“cloud” around
the nucleus.
• The number of protons and
electrons an atom has is unique
for each element.
Atomic Charge
• Atoms have no overall charge
because the protons (+) cancel
out the electrons (-).
Helium
2 protons - +2
2 neutrons 0
2 electrons - -2
total charge 0
Protons
• positive (+) charge
• Found in the nucleus
• # of protons = atomic #
• The number of protons identify
the element (atomic #)
Neutrons
• no charge
• Found in the nucleus
• Along with protons makes up
atomic mass
• Atomic Mass – atomic number = # of neutrons
(rounded to whole #)
Electrons
• negative (–) charge
• travel in orbitals (or energy levels)
around the nucleus. (electron cloud)
• Equals atomic number in neutral
atoms
• valence electrons - the # of
electrons in the outer shell and
relates to the oxidation #
• Unit of measure for atomic
particles is Atomic mass unit
(amu) protons and neutrons =
about 1 amu (electrons are
about 1/2000 of the size of
protons and neutrons))
Chemical symbols
• The one or two letter abbreviation
of the element name.
• Some are based on Latin name
• ALL 1st letter is upper case
• ALL 2nd letter is lower case
Mass Number or Atomic Mass
• the sum of the number of protons
and the number of neutrons in the
nucleus of an atom.
• # of neutrons =
Neutrons
mass # - atomic #
Protons
+
Atom Summary
• Atomic Number = protons = electrons
• Atomic Mass = Protons + Neutrons
• Neutrons = atomic mass – atomic number
• Atomic symbols
– First letter is ALWAYS upper case
– Second letter is ALWAYS lower case
• Example:
Oxygen element 6 with mass 16
P=8
E=8
N = 16-8 = 8
Isotopes
• Atoms of the same element that
have a different # of neutrons and a
different atomic mass. (identified by
the element name followed by the
mass # )
• ex. C-12, C-14, B-10, B-11)
Carbon 14 = 8 neutrons 6 electrons
6 protons 6 protons
6 electrons Carbon 12 = 6 neutrons
Average atomic mass
• the weighted - average mass of the
mixture of all an atoms isotopes.
The average atomic mass is close
to the mass of its most abundant
isotope.
• This is the number found on the
periodic table