Elements, Atoms, and Ions
Elements cannot be broken down by
ordinary chemical change to simpler forms
of matter.
Metals, nonmetals, metalloids (semimetals)
Each element is assigned a unique
chemical symbol.
METALS -- shiny, conduct heat and electricity,
ductile (can be pulled into wires), malleable
(can be rolled into sheets)
NONMETALS -- dull, brittle, poor conductors
METALLOIDS -- have properties of both
metals and nonmetals
POSITION ON PERIODIC CHART
Each element has a unique one- or two-letter
symbol.
First letter is always capitalized and the second
is not.
The symbol usually consists of the first one or
two letters of the element’s name.
Examples:
Oxygen O
Krypton Kr
Sometimes the symbol is taken from the
element’s original Latin or Greek name.
Examples:
Gold Au aurum
Lead Pb plumbum
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Iron -- Fe -- ferrum
Lead -- Pb -plumbum
Copper - Cu - cuprum
Mercury-Hghydrargyrum
Gold -- Au -- aurum
Silver-Ag- argentum
Antimony-Sb-stibium
Sodium -Na-natrium
Potassium -K- kalium
tin- Sn - stannum
From the Greek, atomos meaning “not cut”
Law of Conservation of Mass:
No detectable gain or loss of mass occurs in
chemical reactions. Mass is conserved.
Law of Definite Proportions:
In a given chemical compound, the elements are
always combined in the same proportions by
mass.
Water always contains 8 g of oxygen for every 1 g of
hydrogen.
Carbon dioxide always contains 2.7 g of oxygen for
every 1 g of carbon.
1. Matter consists of tiny particles called atoms.
2. Atoms are indestructible. In chemical
reactions, the atoms rearrange but they do
not themselves break apart.
3. In any sample of a pure element, all the atoms
are identical in mass and other properties.
4. The atoms of different elements differ in mass
and other properties.
5. In a given compound the constituents atoms
are always present in the same fixed
numerical ratio.
Postulated the existence of electrons using
cathode-ray tubes.
The atom must also contain positive particles
that balance exactly the negative charge carried
by particles that we now call electrons.
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Reasoned that the atom
might be thought of as a
uniform “pudding” of
positive charge with
enough negative electrons
scattered within to
counterbalance that
positive charge.
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Explained the nuclear atom.
Atom has a dense center of positive charge
called the nucleus.
Electrons travel around the nucleus at a
relatively large distance.
A proton has the same magnitude of charge as
the electron, but its charge is positive.
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Most nuclei also contain a neutral particle
called the neutron.
A neutron is slightly more massive than a
proton but has no charge.
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Flash Animations
Electrons – found outside
the nucleus; negatively
charged
Protons – found in the
nucleus; positive charge
equal in magnitude to
the electron’s negative
charge
Neutrons – found in the
nucleus; no charge;
virtually same mass as a
proton
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The nucleus is:
Small compared with the overall size of the
atom.
Extremely dense; accounts for almost all of
the atom’s mass.
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The chemistry of an atom arises from its
electrons.
Electrons are the parts of atoms that
“intermingle” when atoms combine to form
molecules.
It is the number of electrons that really
determines chemical behavior.
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Atomic number = # of protons.
In a neutral atom the number of protons equals
the number of electrons.
Mass number = number of protons plus the
number of neutrons.
Mass number minus the atomic number equals
the number of neutrons.
Atomic mass -- mass of an element relative
to the carbon 12 isotope. C --12 is assigned a
mass of 12 atomic mass units and the masses
of other elements are determined relative to
it.
Atomic mass unit (amu) = 1/12 the mass of
the C -- 12 isotope.
Isotopes -- atoms having the same number
of protons but a different number of
neutrons.
Ions -- atoms that have acquired a charge by
gaining or losing electrons. Metals usually
lose electrons and nonmetals usually gain
electrons. Metallic ions normally have a +
charge and nonmetallic ions a negative
charge.
Cation (+ ion) and anion(- ion)
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A
Z
X
X = the symbol of the element
Z = the atomic number (# of protons)
A = the mass number (# of protons and
neutrons)
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The periodic table shows all of the known elements
in order of increasing atomic number.
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1. History
Döbereiner -- Law of Triads
Newlands -- Law of Octaves
Meyer -- worked with physical properties of
elements
Mendeleev -- worked with chem properties
and arranged according to atomic mass.
Moseley -- arranged elements according to
increasing atomic number. This is how the
periodic chart is arranged today.
2. Vertical columns -- families -- similar
chem and physical properties.
3. Horizontal rows -- periods or series -- go
from metallic to nonmetallic properties.
4. Central section -- transition elements
5. Bottom, separated two rows -- rare earth,
inner transition elements; lanthanide &
actinide series.
The periodic table shows all of the known elements
in order of increasing atomic number.
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Most elements are metals and occur on the left
side.
The nonmetals appear on the right side.
Metalloids are elements that have some metallic
and some nonmetallic properties.
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1.
2.
3.
4.
Efficient conduction of heat and electricity
Malleability (they can be hammered into thin
sheets)
Ductility (they can be pulled into wires)
A lustrous (shiny) appearance
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