Download Changes in matter

Everything around you is
matter. All matter is made up
of elements, the smallest unit
of which is the atom, and is
described by its properties
and composition.
1)
Atoms, Molecules, and Compounds
a) Basics of atomic structure: nucleus,
protons (positive charge), neutrons
(neutral), electrons (negative charge)
b)Atoms are constantly in motion; electrons
move around the nucleus in paths called
shells (or energy levels).
c)Atoms may join together to form
molecules and compounds.
d)Common compounds and their formulas:
Water: H20, “Table” salt: NaCl, Carbon
dioxide: CO2
 People
have been
thinking about
matter for more
than 2, 500 years. It
was widely
believed that all
matter was
composed of four
elements – earth,
air, fire, and water
 In
1803, scientist
and school teacher
John Dalton came
up with a precise
definition for the
invisible unit we
call the atom
today.
 We
now know that
atoms have an
internal structure
and area made of
even smaller parts
known as subatomic
particles. These
particles are
protons, neutrons,
and electrons.
 Protons
are
particles in the
nucleus of an atom
that have a positive
(+) charge.
 Neutrons
are
uncharged
(electrically
neutral) particles
that are also
contained in the
nucleus of an atom
 Electrons
are
negatively (-)
charged particles
that spin around the
nucleus.
 Protons
and
electrons have
exactly equal (but
opposite) charges,
so an atom tries to
stay electrically
“neutral” by having
the same number of
protons and
electrons.
(Note that the number of
electrons in any given
atom is equal to its
number of protons.)
 Normally, an
atom contains an equal
number of electrons and protons, making
the whole atom electrically neutral. This
means that the negative charges of the
electrons balance the positive charges of
the protons in the atom.
 If
an atom loses any
electrons , the atom become
positively charged, and if it
gains more electrons than
protons, the atom becomes
negatively charged.
 These positively and
negatively charged atoms
are called ions.
When an object
discharges, it loses the
excess electrons and
becomes neutral again.
Like charges repel and
unlike charges attract.
 Two
or more atoms
that are chemically
combined are called
Molecules.
 Share one another’s
electrons.
 A water molecule
consists of two
hydrogen atoms that
are bonded to an
atom of oxygen.
2)
Elements
a) Elements have atoms of only one kind,
having the same number of protons.
There are a little more than 100 different
elements.
b)The periodic table organizes elements
with common properties.
c)Atomic symbol and atomic number
d)Well known elements and their
symbols
2)
Elements
e) Two important categories of elements:
metals and non-metals
f) Metals compose about 2/3 of the
known elements.
g) Properties of metals: Most are shiny,
ductile, malleable, conductive.
 Matter
is composed
of elements.
 Gold, silver, and
aluminum, are all
elements.
 They are pure
substances that
cannot be broken
down into simpler
substances.



In 1869, Dmitri Ivanovitch
Mendeléev created the first
accepted version of the periodic
table.
He grouped elements according to
their atomic mass, and as he did, he
found that the families had similar
chemical properties.
Blank spaces were left open to add
the new elements he predicted
would occur.
The Periodic Table arranges all elements
according to their atomic number.
atomic number = number of protons
The table identifies elements with similar
chemical properties.
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 Some
elements you
may know:
 Oxygen – to breathe
 Helium – makes
balloons float
 Calcium – helps
make your bones
strong
 Iron – to stay
healthy and strong





Metals are good conductors
of heat and electricity.
Metals are shiny.
Metals are ductile (can be
stretched into thin wires).
Metals are malleable (can
be pounded into thin
sheets).
A chemical property of
metal is its reaction with
water which results in
corrosion.
• A molecule consists of two or more atoms of
the same element, or different elements, that are
chemically bound together.
• In the animation above, two nitrogen atoms
(N + N = N2) make one Nitrogen molecule .
 Elements-
simplest kind of matter
• cannot be broken down any simpler and still
have properties of that element!
• all one kind of atom.
 Compounds are substances that can be broken
down only by chemical methods
• when broken down, the pieces have
completely different properties than the
original compound.
• made of two or more atoms, chemically
combined (not just a physical blend!)
• Atoms of two or more different elements
bound together.
• Can be separated into elements chemically,
but not physically.
In the animation above, water (H20) is a compound made of
Hydrogen and Oxygen.
Animated images and notes from http://www.chem.purdue.edu/gchelp/atoms/elements.html
Atoms
• The building blocks of Matter
• Consists of Protons (+), Electrons (-),
and Neutrons (N).
Elements
• Consists of only one kind of atom,
• Cannot be broken down into a simpler type of matter
by either physical or chemical means
• Can exist as either atoms or molecules.
Images are from http://www.chem4kids.com
Molecules are groups of atoms held
together in a stable association.
Compounds are molecules containing
more than one type of element.
Atoms are held together in molecules or
compounds by chemical bonds.
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1)
Describe that matter is neither created nor destroyed
even though it may undergo change.
a)Compare the total weight of an object to the weight of its
individual parts after being disassembled.
b)Compare the weight of a specified quantity of matter
before and after it undergoes melting or freezing.
c)Investigate the results of the combined weights of a
liquid and a solid after the solid has been dissolved and
then recovered from the liquid (e.g., salt dissolved in
water then water evaporated).
d)Investigate chemical reactions in which the total weight
of the materials before and after reaction is the same
(e.g., cream and vinegar before and after mixing, borax
and glue mixed to make a new substance).
3)
Chemical and Physical Change
a) Chemical change alters the
composition of a molecule and results in
a new substance with a new molecular
structure. Examples of chemical change
are the rusting of iron, the burning of
wood, and milk turning sour.
3)
Chemical and Physical Change
b)Physical change alters only the
properties or appearance of the
substance, but does not change what the
substance is made up of. Examples of
physical change are cutting wood or
paper, breaking glass, and freezing
water.
Physical or Chemical
Change?
•Burning Paper
•CHEMICAL
Physical or Chemical
Change?
•Digestion of food
•CHEMICAL
Physical or Chemical
Change?
•Sugar dissolving in
water
•PHYSICAL
Physical or Chemical
Change?
•Iron turning red
when heated
•PHYSICAL
Physical or Chemical
Change?
•Evaporation
•PHYSICAL
Physical or Chemical
Change?
•A pond freezing in
winter
•PHYSICAL
Physical or Chemical
Change?
•Melting ice
•PHYSICAL
Physical or Chemical
Change?
•Cutting wire
•PHYSICAL
Physical or Chemical
Change?
•Baking muffins
•CHEMICAL
Physical or Chemical
Change?
•Shattering glass
•PHYSICAL
Physical or Chemical
Change?
•Decomposition of
old leaves
•CHEMICAL