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ATOMS & THE PERIODIC
TABLE OF ELEMENTS
Chapter 3
CLASSIFYING MATTER
• What is matter made of?
• The ancient Greeks thought that everything in the
universe was made up of a combination of 4
“elements”: air, fire, water, and earth. People believed
this for many centuries!
• In the late 1600s, early chemists began to discover that
this was not the case, that there are more than 4
elements and they are not what the Greeks thought
they were.
• Now we know that all matter in the universe is made up
of over 100 different kinds of elements.
ELEMENTS
• An element is a substance that cannot
be broken down into any other
substance by physical or chemical
means (methods or ways).
• Like all matter, elements are identified
by their physical and chemical
properties.
THE ELEMENTS
• Name some elements! Remember, these are
substances that cannot be broken down into
other substances.
• Elements are abbreviated by one or two letter
symbols
• Examples: oxygen is O, calcium is Ca, carbon is C,
aluminum is Al)
• Link
ATOMS
• What would happen if you tore a piece of
aluminum foil into smaller and smaller
pieces? What is the smallest possible piece of
a substance?
• All matter is made up of atoms.
• An atom is the particle out of which all
elements are made.
MOLECULES
• Atoms can combine and form a chemical bond, or a
force of attraction between 2 or more atoms.
• A molecule is a group of 2 or more atoms held together
by chemical bonds
• A molecule can be made of the same atoms or several
different atoms
• Examples: O2, H20, CO2, NH3
• How can oxygen (O2) be both an element and a
molecule?
• It is two or more atoms but they are the same element
COMPOUNDS
• A compound is a substance made of 2 or
more elements that are chemically
combined in a certain ratio.
• For example, carbon dioxide (CO2) is 1atom
of carbon and 2 atoms of oxygen. Carbon
monoxide (CO) is 1 atom of carbon and 1
atom of oxygen.
• Compounds are made of molecules.
• Table sugar has the chemical formula C12H22O11.
What is the ratio of carbon to oxygen in this
compound?
• 12:11
• Is H2O the same as H2O2? Would you expect them
to have the same properties?
• No, they are different substances (H2O2 has one more
oxygen) so they would have different properties.
BELLRINGER
•Without using a
periodic table,
what elements
are
represented by
the symbols O,
C, H, and Cl?
•The properties of compounds are
different that those of the elements
they are made of.
•Example: sodium (Na) + chloride (Cl) =
salt (NaCl)
•Why??
•Because Na and Cl are different
substances.
WHAT IS AN ATOM MADE OF?
• Positive center (nucleus) with a cloud of
negatively charged particles around it
• Proton: positive (+), in nucleus
• Neutron: neutral (0), in nucleus
• Electron: negative (-), “orbits”
nucleus in energy levels
SUBATOMIC PARTICLES
• The proton of an atom of gold is
the same as a proton of oxygen.
Same for electrons and neutrons!
All protons, neutrons, and electrons
are the same. What makes
elements different is the relative
numbers of each.
ATOMIC NUMBER
• # of protons = atomic number
• Defines each element
• How the elements are arranged
on the periodic table
• Number of protons equals number
of electrons (unless it is an ion, or
atom that is charged)
• Atoms of one element are
different from atoms of another
element because of their number
of protons (atomic number)
• Draw an atom of
helium. Helium has 2
electrons, 2 protons,
and 2 neutrons.
ISOTOPES
• Isotopes are atoms with a same number of protons but
different number of neutrons
• Isotopes are identified by their mass number (sum of protons
+ neutrons)
• Electrons have very little mass
• With a partner, on a blank sheet of paper,
write the names of as many elements as you
can think of (do not use a periodic table!)
• Now organize them into groups based on their
characteristics. Every group must have more
than one element in it.
THE PERIODIC TABLE
• Russian chemist Dmitri
Mendeleev organized the
elements into the Periodic
Table in the 1870s
• Puzzle of the Periodic Table
• He did this by studying each
element’s melting point, density,
color, and atomic mass
(average mass of all isotopes of
that element)
• He predicted the existence of
many elements that were
discovered later!
THE PERIODIC TABLE
• Most periodic tables include the atomic number,
chemical symbol, name, and atomic mass of each
element
• Where did all the elements come from?
• All elements up to iron were created in stars,
elements heavier than iron come from supernovas
• How did they get their names?
• Names of scientists, places, Latin/Greek, etc.
• Element Song
THE PERIODIC TABLE
• Although the Periodic Table is arranged by increasing atomic number, it
is the arrangement of each element’s electrons that determines its
properties
• There are 7 possible energy levels for electrons and 7 periods (rows) on
the periodic table
• The periods go in order of increasing atomic #
• Elements in a group (column) have the same number of outermost
(valence) electrons and react similarly
• Noble gases are unreactive because their valence orbitals are full
• Metals are on the left of the table, nonmetals on the right, and metalloids
in between
• You can predict the properties of an element by knowing where it is on
the Periodic Table!
11/24/14
•Bellringer: How many
electrons does this
element have? How
many neutrons does it
have?
METALS
• Most elements on the Periodic Table
• Have physical properties like luster
(shininess), malleability (can be
hammered flat), ductility (can be made
into wires), conductivity (good
conductors of heat & electricity)
• Metals usually react by
losing electrons
• When metals deteriorate
due to chemical reactions
with substances in the
environment (like oxygen
or water) it is called
corrosion.
• Example of corrosion: rust
METALS
METALS
• Alkali metals (group 1) are the most reactive metals
• Are never found uncombined (alone) in nature
• Alkaline earth metals (group 2) are harder, denser,
and melt at higher temps, and are less reactive
than the alkali metals
• Transition metals (group 3-12) are hard, shiny, with
high melting pts and densities, less reactive
NON-METALS
• Lack the properties of metals
• Poor conductors, dull, brittle
• Many are gases at room temp; some are solids
(C, S, I), bromine is the only liquid
• On the right side of Periodic Table (except
Hydrogen)
• Usually gain or share electrons when they
react
NON-METALS
• Halogens (group 17), like
chlorine, are the most
reactive nonmetals
• Noble gases (group 18),
like neon, are usually
nonreactive
METALLOIDS
• Metalloids have some properties of metals and
some properties of nonmetals
• Examples are silicon & arsenic
RADIOACTIVE DECAY
• Remember what an isotope is..
• An atom that has a different # of neutrons than usual
• Some isotopes are unstable, meaning they undergo
radioactive decay
RADIOACTIVE DECAY
• Radioactive decay is when a nucleus gives off alpha or
beta particles and/or energy in the form of gamma rays
• This is a nuclear reaction
• This changes the identity of the atom (because if protons
are lost, the atomic # changes); it becomes a new
element
• Something is radioactive if it does radioactive decay
RADIOACTIVE DECAY
• Radioactive dating is using isotopes to determine
how old something is
• This is done by knowing the half life of the isotopes,
or how long it takes for half of it to decay
• Isotopes are also used as tracers (see where things
go)