Transcript Unit 1 Matter Day 32 2016 Counting Atoms

UNIT 1 MATTER DAY 32
OCTOBER 14, 2016
Counting Atoms
8th Grade Science
OCTOBER 14, 2016
3rd period – I need 2 students to
play the “Ships and Sailors”
game at the pep rally today.
Santi and Zac are still doing
the relay.
4th period – No walk today.
Figure it out!
Pick up a copy of the notes “Law
of Conservation of Mass/Balancing
Chemical Equations” from the lab
table, and be seated.
Plan for today:
1. Lesson on chemical formulas and
chemical equations
2. Practice counting atoms in compounds
3. 4th period – Review quiz on elements,
compounds, and mixtures
4. Bill Nye “Chemical Reactions” video, if
time permits
Homework:
Worksheet “How to Count Atoms” and
“Counting Atoms”.
E.Q Page _____
How do balanced chemical equations
demonstrate the Law of Conservation of
Matter?
CHEMICAL FORMULAS
 Def.
Chemical formula is a combination of
chemical symbols and numbers to represent a
substance.It shows how many atoms of each
kind of element are present in a molecule.
 Subscript: a number written to the lower right
of a chemical symbol. It tells how many atoms
of that element are present.
Copy these 3
examples.
CHEMICAL
EQUATIONS
•Def. Use chemical
symbols and
formulas to
describe a chemical
reaction.
•Ex: Copy this
Chemical equation.
•C and O2 are the
reactants. CO2 is
the product.
yields
 *Coefficient:
a number that is placed in
front of a chemical symbol or formula in
order to balance a chemical equation.
Subscripts (the little numbers) CANNOT be
changed to balance an equation. Why?
 H 2O
 CO2
 C6H12O6
2H20 -2 molecules
of water
4CO2 – 4 molecules
of carbon dioxide
RULES FOR COUNTING ATOMS:
Subscripts (the little numbers) tell you how many
atoms of that element are present. H2O = 2 atoms of
hydrogen and one atom of oxygen
 If a coefficient (big number) is written in front of a
chemical formula or symbol, you have to multiply that
number by all the elements in the compound.
Ex. 2NaCl (think about the distributive property
in math) 2(NaCl) – this would mean 2 atoms of
sodium (Na) and 2 atoms of chlorine (Cl) OR
2 molecules of sodium chloride
 If a compound contains subscripts and coefficients, you
have to multiply the coefficients by the subscripts.
Ex. 2Na2SO4 or 2(Na2SO4) = 4 sodium (Na) atoms, 2
Sulfur atoms, and 8 oxygen atoms

LET’S PRACTICE
COUNTING ATOMS IN
PREPARATION FOR
LEARNING HOW TO
BALANCE CHEMICAL
EQUATIONS.
STOP HERE – SHORT CLASSES DUE TO PEP
RALLY
CHEMICAL FORMULAS
 Def.
Chemical formula is a combination of
____________ ___________and ____________ to
represent a ___________.It shows how many
__________ of each kind of ___________ are
present in a ____________.
 Subscript: a number written to the _________
__________ of a chemical ___________ . It tells
how many ___________ of that element are
present.
CHEMICAL EQUATIONS
•Def. - Use chemical ____________ and
____________ to describe a ____________
____________.
LAW OF CONSERVATION OF MASS
Def. This law states that matter(mass) CANNOT be
created or destroyed in ordinary physical or
chemical changes.
 The total mass of the reactants equals the total
mass of the products.
 This can be proven in a closed
system… one in which nothing enters or leaves the
system.

LAW OF CONSERVATION OF MASS
Def. This law states that ______________ CANNOT be
_____________ or _____________ in ordinary
______________or ________________ ________________.
 The total __________________________________________
______________________________________________________.
 This can be proven in a __________ ___________…one
in which nothing enters or leaves the system.

Let’s look at the Law of Conservation of
Mass and Chemical Equations presented
Brainpop’s way.
Brainpop - Law of Conservation of Matter
A Quick Review
elements
Chemical symbols represent __________.
compounds
Chemical formulas represent __________.
chemical reactions.
Chemical equations represent __________.
Now let’s learn how to balance
chemical equations.
A Quick Review
Chemical symbols represent __________.
Chemical formulas represent __________.
Chemical equations represent __________.
Now let’s learn how to balance
chemical equations.
 *Coefficient:
a number that is placed
____________ a chemical _________ or
_________ in order to __________ a
chemical ___________. Subscripts
__________ be _________ to balance an
equation. Why?
 H2 O
 CO2
 C6H12O6
2H20 -2 molecules
of water
4CO2 – 4 molecules
of carbon dioxide
More O2 in the
reactants.
Count to be sure the number of atoms of each
element is the same in the reactants and
products.
How to Balance Chemical Equations: 3 Simple
Steps
Step 1: Count the number of atoms for
each element on both sides of the
equation. Look for elements that are not
balanced.
Ex.
Mg
+ O2
MgO-
_____ is unbalanced.
MgO
MgO-
Step 2: Add a coefficient in front of the
formula that contains the unbalanced element(s). The
O was unbalanced. Place a coefficient 2 in front of
the MgO. ***Note: This may throw off the balance
of other elements, so you have to keep working with
it.
Ex. Mg + O2
__ MgO
This will balance the O, but unbalance the Mg.
So…add another coefficient 2 in front of the Mg in
the reactant.
Ex. ___Mg + O2
2 MgO
*This should balance the Mg but be sure to do Step
3.
Step 3:
Check the number of atoms on both
sides of the equation to be certain they are
balanced.
2Mg + O
MgO-
2MgO
MgO-
Is it balanced? If so, you have supported the Law of
Conservation of Matter (Mass).
How does balancing equations illustrate and
support the Law of Conservation of
Mass/Matter?
*Because they require that you have the
same mass after the reaction as you do before
the reaction. This means…
*The # and type of atoms are the same in the
reactants and products (just in different
combinations)
*Although the state of matter of the products
may be different from the reactants, the
overall mass doesn’t change.
Let’s look at Chemical Equations presented
Brainpop’s way.
Brainpop-Chemical Equations
Before we practice balancing
equations, let’s practice counting
atoms.
Practice Counting Atoms
worksheet
Let’s practice balancing some chemical
equations. “Balancing Act” practice sheet.
Use pencil. You may have to change
coefficients a few times.
In
a chemical reaction, no atoms are
gained or lost. They just get
rearranged.
Because this Law of Conservation of
Matter (Mass) has been proven,
chemical equations (which represent a
chemical reaction) MUST be balanced
(same number of atoms on both sides).
mass of the reactants=mass of the
products.
Wrap-up:
Any questions?