Chapter 11
The Atomic Nature of Matter
Atoms
• Building blocks of matter
• Everything is composed of atoms
Elements
• atoms of the same kind
• there are 115 known elements to date
• Every element is unique, and has its own set of
properties
• All atoms of the same element have the same #
of protons.
Atoms are recyclable
• the same atoms have been here since the
beginning of time
• Combine w/ other elements, then go back to
original form and back again
• You may be breathing the same air as Julius
Caesar or George Washington….
Atoms are very small
• Cannot view individual atoms w/ visible light
• Only way to “see” atoms is w/ Scanning Tunneling
Microscope
• About 1023 (or
1000000000000000000000000000) atoms in
one thimble-full of water
Brownian Motion
• Jiggling of atoms
• Atoms are constantly moving
• Molecular motion never stops unless a substance is
at a temperature of (-273˚ C) a.k.a. absolute zero
Molecules
• combinations of atoms ex. H2, H2O, NaCl, N2
• Can be combinations of the same atom, or of
different types of atoms
Compounds
• combinations of atoms of different elements ex.
NaCl, H2O, HCl
• A compound is always a molecule, but a
molecule may not necessarily be a compound
(examples …. H2 , N2 )
Rutherford Experiment
• Gold Foil - showed atoms are largely empty
space, very dense nucleus that reflected charged
particles backwards
• Like a “shooting a 15-inch artillery shell at a
piece of tissue paper and having it come back
and hit you”
Nucleus
• very dense……. Composed of Protons &
Neutrons
• Almost all of the mass of an atom is
concentrated in the nucleus
• A teaspoonful of nuclei packed together would
weigh a billion tons
Neutrons & Protons
• Nuetrons- Neutral charged particle found in
nucleus
• Protons- Positively charged particle found in
nucleus, atoms of the same number of protons
are atoms of the same element
Isotopes
• for a given element, the number of neutrons may
vary. Isotopes of an element are atoms of the
same element having different numbers of
neutrons
• Example - Uranium-238 (atomic mass 238) has
isotope Uranium -235
▫ This was used to make the atomic bomb dropped
on Hiroshima
Electrons (e-)
• negatively charged particle not found in the nucleus.
• Orbits the nucleus in various energy levels.
• In a neutral atom, the number of electrons will match
the number of protons
• # of electrons in a neutrally charged atom is equal to
the # of protons, which is given with the atomic
number.
• Mass of 1 electron is about 1800 times less than the
mass of a proton or neutron
Ions
• Charged Particle
▫ Positively charged (less electrons than protons)
▫ Negatively charged (more electrons than protons)
• not all atoms are neutral. This happens when the
number of electrons is more than, or less than
the number of protons.
▫ The number of protons never changes,
▫ however the number of electrons can change
often.
Shell Model of an Atom
• Electrons occupy different shells.
• 2 maximum electrons may fit in the first shell
• The next shell holds 8 electrons, and the largest
shell will hold 50 electrons.
• For example, if an atom has 13 electrons, it will
have 2 in the first shell, 8 in the second shell,
and the remaining 3 will go in the third shell.
Periodic Table
• chart that lists atoms by their atomic number
and by their electron arrangement.
• As you move from left to right on chart each
element gains one proton and electron .
• As you go down each column each element has
one more shell filled than the element above.
• Elements in the same column are in a Group.
Groups have similar properties.
• Atomic Number - number of protons in the nucleus
• Atomic Mass – equals the average mass (in atomic
mass units) of the nucleus
▫ # of Protons = Atomic Number
▫ # of Electrons = # of Protons, (if molecule has no
charge)
▫ # of Neutrons = (Atomic mass (rounded)) - (atomic
number)
Phases of Matter
• Solid, Liquid, Gas – three familiar states of
matter. In all phases, atoms are in constant
motion.
• The more the molecules move the more fluid they
become,
▫ Solid – molecules have least energy, stay fixed
relative to each other
▫ Liquid- molecules have more energy, molecules
move relative to one another
▫ Gas – molecules have most energy, move with large
distances between each other
Plasma – the 4th State of Matter
• Consists of positive ions and free electrons.
Exists only at high temperatures.
• What sun and stars are made of. Can be seen
here on Earth in the glowing gas of fluorescent
lamps.