Transcript TAKS 8 th Grade Science Review Objective 3

TAKS 8th Grade Science
Review
Objective 3
Structures and Properties
of Matter
Remember all the
information given to
you on this page!
Information from the Periodic Table
• Groups – columns (18) – elements with similar
physical and chemical properties
• Periods – rows (7) – energy levels of the
outermost electrons (valence electrons)
• Valence Electrons – farthest from the nucleus or
most loosely held (key to how an atom reacts!)
Note the locations of the metals, halogens and
noble gases.
Elements found in which shaded area of
this periodic table undergo the fewest
chemical reactions?
AQ
BR
CS
DT
Element Information
Atomic Number
Number of Protons +
Symbol
Starts w/ a Capital
Atomic Mass
Protons + + Neutrons n
Name of Element
6
C
-
12.011
Carbon
How do you determine the number of Neutrons n ?
Subtract the Atomic Number from the Atomic Mass 12 – 6 = 6
n
n ++ n
+ +n +
n +
n
-
-
-
+ n - += n
How do you determine the number of Electrons - ?
In a stable atom, the number of protons equals the number of electrons 6 = 6 + = -
Parts of an Atom
Part
n
+ +
n n n
+ + ++ n
n n n
+ +
-
Location
Protons Positive + Nucleus
Neutrons Neutral n Nucleus
Electrons Negative - Orbit
-
O
+
Charge
H
Valence Electrons –
farthest from the nucleus or
most loosely held (key to
how an atom reacts!)
Dot Diagram – consists of
the symbol for an element
surrounded by the number of
valence electrons
Atom vs Molecule
Atom – the smallest
particle of an element
n
+ +
n n n
+ + ++ n
n n n
+ +
-
-
Molecule – a combination
of two or more atoms
bonded together
n
+ +
n
n n
+
+ + + n
n n n
+ +
+
+
What is this element?
Which molecule does this
represent?
TAKS Questions
A certain atom has a nucleus containing six
protons and eight neutrons and has six
electrons orbiting the nucleus. This atom is a
form of the element —
A silicon
B carbon
C magnesium
D calcium
Ions
• Ions are atoms with either extra electrons or missing
electrons.
• A normal atom is called a neutral atom, that is an atom
with a number of electrons equal to the atomic number.
You are a sodium (Na) atom. You have 11 - , one too many to have
your outer shell filled. You need to find another element who will
take that - away from you. Bring in chlorine (Cl). Chlorine (Cl) will
take that electron away and leave you with 10 - inside of two filled
shells. You are a happy atom. Now you are also an ion, missing 1 - .
You are a sodium ion (Na+). You have one less electron than your
atomic number. What about the chlorine atom? Is it an ion?
-
+
+
NaCl
Sodium Chloride
Isotopes
Let's say an atom is missing a neutron or has an extra neutron. That
type of atom is called an isotope. An atom is still the same element if
it is missing an electron. The same goes for isotopes. They are still
the same element. They are just a little different from every other
atom of the same element. Let’s look at carbon isotopes.
There are a lot of carbon atoms in the universe. The normal ones are
carbon-12. Those atoms have 6 neutrons. There are a few straggler
atoms that don't have 6. Those odd ones may have 7 or even 8
neutrons. Carbon-14 actually has 8 neutrons (2 extra). C-14 is
considered an isotope of the element carbon.
RETURNING TO NORMAL
If we look at the C-14 atom one more time we can see that C-14 does not last forever.
There is a point where it loses those extra neutrons and becomes C-12. That loss of the
neutrons is called radioactive decay. That decay happens regularly like a clock. For
carbon, the decay happens in a couple of thousand years. Some elements take longer
and others have a decay that happens over a period of minutes.
Practice with Molecules
Symbol
Element
Atomic
Number
Atomic
Mass
Protons
Electrons
Neutrons
Na
Sodium
20
40.8
20
20
20
80
6
2
H
6
Co
120
Au
47
Interpreting Chemical Formulas
CO2
3Fe2O3
2C6H12O
C 1
Fe 2 x 3
6
6
C 6 x 2 = 12
O 2
O 3 x3
9
H 12 x 2 = 24
O 6 x 2 = 12
• List your elements
• How many atoms of each element? The number behind
the symbol. If there is no number behind the symbol,
there is 1 atom of that element.
• Multiply by the number of molecules (coefficient - the
number in front)
Practice with Compounds
Chemical
Formula
Element 1
Element 2
Number of
Atoms
(Element 1)
Number of
Atoms
(Element 2)
Atomic
Mass 1
Atomic
Mass 2
Atomic
Weight
H2O
Hydrogen
Oxygen
2
1
1.008 x 2
16 x 1
18.016
CO2
KCl
Fe2O3
(PO4)2
AgBr
HCl
MgO
Law of Conservation of Mass
• Two lab students in IPC class mix calcium with zinc carbonate.
According to the law of conservation of mass, what other product
was produced and how much?
A
B
C
D
0.088 kg of zinc
0.088 kg of calcium
0.104 kg of zinc
0.104 kg of calcium
Zn
104 g
Balancing Equations
2 Mg +
O2
2 MgO
Mg
1 x 2=2
Mg 1 x 2 = 2
O
2
2
O
3
4
1 x 2=2
2
4
1. List your elements
2. How many atoms of each element?
3. Multiply by the number of molecules (coefficient)
4. Total. If they are even on both sides, the equation is balanced.
5. Balance the equation by adding molecules only! (Use multiplication)
TAKS Questions
K + H2O → KOH + H2
What is the coefficient for H2O when the
above equation is balanced?
A1
B2
C3
D4
Types of Chemical Reactions
• Have you heard of Hydrogen Peroxide?
• What are some of its uses?
H 2O 2  H 2O + O 2
• What happens to H2O2?
• What happens when something decomposes?
Decomposition Reaction
• The breakdown of hydrogen peroxide is
known as a decomposition reaction.
• Let’s balance the chemical equation:
___H2O2  ___H2O + ___O2
Single and Double Replacement
Reactions
A
B C
BA
C
Cl2 + NaBr
NaCl + Br2
A
BC
Mg + HCl
A C
B
MgCl2 + H2
A B
C D
K2SO4 + CaCl2
A B
C D
Al(NO3)3 + NaOH
AD
C B
KCl + CaSO4
A
D
C B
Al(OH)3 + NaNO3
Recognize this chemical reaction!
• Plants use carbon dioxide and water with sunlight to
provide animals sugar, oxygen and energy.
• Help us translate this sentence into a chemical equation.
CO2 + H2O + sunlight  C6H12O6 + O2 + ATP
Respiration
• In the chemical reaction, Respiration, animals produce
some CO2and H2O
• Can we leave the chemical reaction like this? What are
we suppose to do?
__C6H12O6 + __O2  __CO2+ __H2O
Balancing Equations
Mg +
O2
Cl2 + NaBr
CO2 + H2O
MgO
Mg +
NaCl + Br2
C6H12O6 +
HCl
K2SO4 +
CaCl2
KCl +
Al(NO3)3 +
NaOH
Al(OH)3 +
MgCl2 +
CaSO4
NaNO3
O2
H2