ELEMENTS AND ATOMS
WHAT ARE ELEMENTS?
• Elements- a substance that cannot
be broken down into anything
simpler.
• They can be solids, liquids, and
gases.
• Elements can exist in pure form and
can be mixed together
• Physically- oxygen and nitrogen are
mixed in the air/
• Chemically- salt is a combination of
sodium (solid) and chlorine (gas)
What if you broke a pencil into smaller and
smaller pieces? Eventually the pieces would
be atoms of carbon and other elements.
WHAT ARE ATOMS?
• Atoms- The smallest particles of an
element that have the same
chemical properties as the element.
• The atoms of one element are
different from the atoms of another
element.
• Each element is made up of a
particular type of atom and has its
own special properties.
• Atoms are so small that billions of
atoms fit on the head of a pin.
THE PARTS OF AN ATOM
• Nucleus- the densest part of the atom,
where most of its mass is. The rest of the
atom is just empty space.
• Inside the nucleus are:
• Protons- have a positive electric charge
• Neutrons- have no electric charge.
• The atomic mass (amu) is the sum of the
atoms protons and neutrons.
• Electrons-have a negative electric charge.
• They are smaller than protons and they circle
around the nucleus.
• They are held near the nucleus by an
attraction to the protons.
• An atom has equal numbers of protons,
neutrons, and electrons
HOW HAVE IDEAS ABOUT ATOMS
CHANGED?
• 1803- John Dalton proposed that atoms were solid like marbles
and had no particles inside.
• 1898- J.J. Thompson showed that atoms contained electrons.
He proposed that electrons were sprinkled in positively
charged fluid.
• 1913- Earnest Rutherford and H.G.J Moseley showed that
positive matter in atoms was packed into a tiny nucleus.
• 1926- Scientists have thought of electrons as “clouds”
surrounding the nucleus.
• Atomic Number- atoms in each element has a unique number
of protons. Thus number is used to classify the atom.
• Isotopes- atoms that have the same number of protons but a
different number of neutrons.
WHAT IS THE PERIODIC TABLE?
• 1868- Dmitry Mendeleyev tried to arrange the
elements in a different way. He discovered the
modern periodic table of elements.
• He arranged them by atomic mass a discovered a
repetitive pattern of several properties (density,
metal character, and ability to react with other
elements).
• Why was he so successful?
• He left blank spaces in the table when necessary to
keep the periodic pattern.
• He predicted that elements would be discovered to fill
them.
• He was correct. Eventually other atoms were discovered
that filled in the blanks.
MORE ABOUT MENDELEYEV
READING THE PERIODIC TABLE
• The elements in the periodic table are
arranged in order of increasing atomic
number.
• Families- the vertical columns contain
elements that react with other substances in
similar ways.
• Period- each row of elements.
• According to their properties, elements can
be placed in one of three groups.
• Metals- conduct heat and electricity, are
shiny when polished, and bend instead of
break.
• Metalloids- have only some properties of
metals.
• Nonmetals- the opposite of metals.
WHAT ARE THE PROPERTIES OF
ELEMENTS?
• Elements have all sorts of different
properties.
• Some are hard, shiny solids.
• Some are clear gases that you
can’t see or taste.
• Others are liquids.
WHAT ARE METALS, NONMETALS,
AND METALLOIDS?
• About ¾ of the elements are metals.
• Metals conduct electricity.
• Example- Copper is used in electrical wiring.
• Nonmetals tend to have the properties opposite
of metals.
• They are poor conductors of electricity.
• They are normally solids of gases at room
temperature.
• Solid nonmetals are brittle instead of bendable.
• Metalloids properties fall between metals and
nonmetals.
• Used to make computer chips and circuits.
Silicon is a metalloid and is used in
computer chip and found in sand.