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Physical Science
SECTION 3.1
Democritus – was a fourth century B.C. Greek philosopher who proposed that the
universe was made up of tiny particles called atoms. The word atom was derived from the
Greek word Atomos, “meaning indivisible or indestructible”.
John 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.
•His theory was accepted because there was evidence to support it.
4 parts of an atom
•Nucleus – is center of an atom that carries a positive charge. It contains both protons &
neutrons. The electrons live outside the nucleus in the electron cloud.
•Neutron – is a neutral subatomic particle in the nucleus of an atom. It carries no charge,
& a mass of 1.66 x 10-24grams = 1amu.
•Proton – is a positively charged subatomic particle in the nucleus of an atom. It carries a
positive charge, & a mass of 1.66 x 10-24grams = 1amu.
•Electron – is a tiny negatively charged subatomic particle moving around outside the
nucleus of an atom. It carries a negative charge, & mass of 9.11 x 10-28grams = 1/1840
amu. Electrons live in the electron cloud outside the nucleus. An electron carries a charge
of -1.
Basic Models of the Atom
•Dalton's model of the atom - solid, tiny, indivisible particles.
•Thomson's model - often describe as the "plum pudding" model - electrons are scattered
throughout the atom.
•Rutherford's model - includes the solid nucleus in the center of the atom.
• Niels Bohr's model - electrons are in fixed orbitals, or energy levels, at certain distances
from the nucleus much the way the planets orbit the sun.
• Quantum mechanical model - the electrons have certain probabilities of being located at
certain places and their positions are described according to four quantum numbers.
There is no way to exactly determine the exact position of an electron. The circle in the
diagram below shows where the electrons have a 90% probability of being within the
electron cloud.
Physical Science
J.J. Thomson – discovered the electron in 1897 with his famous Cathode Ray Tube
experiment. He basically used a magnet to deflect and attract the electrons in the tube.
Ernest Rutherford – discovered the nucleus in 1911 with his famous Gold Foil
Experiment. In this experiment, he aimed alpha particles, “type of radiation” at the gold
foil and was able to determine the protons were all group together in a small area.
James Chadwick discovered the neutron in 1932.
Energy level – any of the possible energies an electron may have in an atom.
Orbital – is a region in an atom where there is a high probability of finding electrons.
Only at most two electrons can occupy an orbital. An orbital with one electron is
considered to be half filled.
Types of Orbitals
s-orbitals – are spherically shaped, have 1 orbital, & hold a maximum of 2 electrons.
p-orbitals – are dumbbell shaped and have 3 orbitals & hold a maximum of 6 electrons.
d-orbitals – are complex in shape and have 5 orbitals & hold a maximum of 10 electrons.
f-orbitals – are complex in shape and have 7 orbitals & hold a maximum of 14 electrons.
Valence electron – an electron in the outer most energy level of an atom (1 – 8 electrons).
•The number of electrons depends on its position on the periodic table.
•Atoms of elements that are in the same group have the same number of valance electrons.
•Valence electrons determine an atom's chemical properties.
SECTION 3.2
Periodic table – is the grouping of all of the elements known to man. The periodic table is
in order by the number of protons inside the nucleus. The number of protons inside the
nucleus is also known as the atomic number.
Period – is a horizontal row of elements in the periodic table.
Group (family) – is a vertical column of elements in the periodic table.
Periodic Law – properties of elements tend to change in a regular pattern when elements
are arranged in order of increasing atomic number, or number of protons in their atoms.
Ionization – the process of adding electrons to or removing electrons from an atom or
group of atoms.
Ion – is an atom or group of atoms that has lost or gained one or more electrons and
therefore has a net electric charge.
•Atoms that have no electrical charge have the same number of protons and electrons.
•A lithium ion is much less reactive than and it’s’ atom because it has a full outermost energy
level.
Physical Science
Cation – is an ion with a positive charge. Atoms that have a positive electrical charge
have more protons than electrons.
Anion – is an ion with a negative charge. Atoms that have a negative electrical charge
have more electrons than electrons.
• Anions have larger radii than cations because they are gaining electrons which extend
their electron cloud from the positively charged nucleus.
Atomic number (Z) – is the number of protons in the nucleus of an atom.
•Example: Sodium has an atomic number of 11 therefore there are 11 protons.
Mass number (A) – is the total number of protons and neutrons in the nucleus of an atom.
• Mass number = protons + neutrons
Atomic mass unit (amu) – is a quantity equal to one-twelfth of the mass of a carbon-12
atom or 1.66 x10-24grams.
•1 Proton = 1 amu
•1 neutron = 1 amu
Average atomic mass – is the weighted average of the masses of all naturally occurring
isotopes of an element. Therefore, it is weighted average, so common isotopes have a greater
effect than uncommon ones.
[Worksheet/Book Work]
Isotopes - any atoms having the same number of protons but different numbers of
neutrons.
Isotopes of Hydrogen
Names
Number of Protons & Neutrons
Mass Number
Protium
1 proton + 0 neutron = 1
A=1
Deuterium
1 proton + 1 neutron = 2
A=2
Tritium
1 proton + 2 neutron = 3
A=3
•Hydrogen makes up less than 1 percent of Earth’s crust.
•Only 1 out of every 6000 of these hydrogen atoms is a deuterium isotope.
[Worksheet/Book Work]
SECTION 3.3
Metals – the elements that are good conductors of heat and electricity.
•Located on the left hand side of the periodic table.
Nonmetals – the elements that are usually poor conductors of heat and electricity.
•Located on the right hand side of the periodic table.
Semiconductors - the elements that are intermediate conductors of heat and electricity.
•Located between the metals and nonmetals.
•Have properties of both metals and nonmetals.
•Also known as metalloids.
Physical Science
Alkali metals – are the highly reactive metallic elements located in Group 1 of the
periodic table. They are extremely reactive because they have one valence electron that is
easily removed to form a positive ion.
•Have 1 valence electron.
Alkaline-earth metals – are the reactive metallic elements located in Group 2 of the
periodic table.
•Have 2 valence electrons.
Transition metals – are the metallic elements located in Groups 3–12 of the periodic
table.
•Transition metals form compounds by losing electrons to form positive ions.
Halogens – are the highly reactive elements located in Group 17 of the periodic table.
•Most halogens form compounds by gaining an electron to form a negative ion.
Noble gases – are the unreactive gaseous elements located in Group 18 of the periodic
table.
•A neon sign is usually reddish orange.
•Adding a little drop of mercury will make the light a bright blue.
•They are inert because their outermost energy level is full.
SECTION 3.4
Mole – is the SI base unit that describes the amount of a substance.
•602213670000000000000000 particles to be exact!
•Is abbreviated mol.
•If the atomic mass of carbon is 12 amu, 1 mole of pure carbon will have a mass of 12g.
Avogadro’s constant – is the number of particles in 1 mol: equals 6.022 ×1023/mol.
•Particles can be the following units: molecules, atoms, ions, and formula units.
Molar mass – is the mass in grams of 1 mol of a substance.
[Worksheet/Book Work]
Conversion factor – is a ratio equal to one that expresses the same quantity in two
different ways.