Counting Atoms
DO NOW MONDAY
• Begin your Pre-Test over Chemistry Unit Part
2.
• When you finish, turn it in to the side cart and
pick up a sheet of notebook paper.
• Number the notebook paper 1-36.
TODAYS PLAN
• To demonstrate Mastery of Chemistry Part 1
Learning Targets on a written Exam.
TODAYS DO
• We will do retake and/or enrichment over
Chemistry Part 1 Learning Targets.
– Made 80% or Greater, you will get a ChromeBook,
go to my Seventh Grade Science page, click on
Periodic Table Enrichment, and play the games on
the websites located there.
– Made less than 80%, you will be using your notes
and asking the teacher questions to redo the
questions you missed on the Chemistry Part 1
Test.
DO NOW TUESDAY
• Tell what you think is the difference between
an element and a compound.
TODAYS PLAN
• Distinguish between symbol and formula.
• Conclude the number of atoms of each element that
exists in a molecule/compound.
• Distinguish between elements and compounds
according to their properties (original vs. after a
chemical change)
• Differentiate between the model of a compound versus
a model of an element.
TODAYS DO
• We will do guided notes about elements, compounds,
and compound formulas.
• We will practice counting the atoms in compound
formulas and drawing models of compounds
Elements
• Are made of atoms
• Are found on the periodic table
• Have chemical SYMBOLS
Element Chemical Symbol
•
•
•
•
Symbol for the element on the Periodic Table
Made up of ONE OR TWO letters
First letter is always capitalized
Second letter, if present, is lowercase
Element
Chemical Symbol
Carbon
C
Aluminum
Al
Fluorine
F
Copper
Cu
Compounds
• Made up of two or more elements chemically
combined
• This means the elements were combined by a
chemical change.
• The atoms of the atoms are held together by
chemical bonds-a “stickiness” between the atoms
that holds them together.
• The compound is a NEW substance and has
different properties than any of the elements that
are in the compound.
• Compounds have chemical FORMULAS.
Examples of Compounds
Element
+ Element
= Compound
Sodium (Na)
+ Chlorine (Cl)
= Sodium Chloride
(NaCl)
+
=
Explosive metal
+ green poison gas = table salt (edible)
Examples of Compounds
Element
+ Element
= Compound
Hydrogen (H)
+ Oxygen (O)
=
(H2O)
+
=
Colorless flammable gas +
colorless flammable gas
Water
=
colorless liquid (edible)
(nonflammable)
COMPOUND CHEMICAL FORMULAS
• All compounds have Chemical FORMULAS.
• These formulas tell us WHAT ELEMENTS are in
the compound
AND
• HOW MANY atoms of each element are in the
compound
COMPOUND CHEMICAL FORMULAS
Tell us:
1. What ELEMENTS
AND
2. HOW MANY ATOMS
Practice
• Tell whether each of the following is an
element or a compound:
1.
2.
3.
4.
5.
Element
I
Br Element
KCl Compound
NaOH Compound
K2CO3 Compound
6.
7.
8.
9.
N Element
Ba Element
CaO Compound
Mn Element
10. N2O3
Compound
Counting Atoms
• The symbol of an element represents ONE
atom of that element
2 atoms total
CO = 1 C and 1 O
• A subscript in a chemical formula is a number
written at the lower right corner after the
symbol for the element. It represents the
number of atoms of an element in a
compound (when there is more than one
atom of that element.
6 atoms total
Na2CO3 = 2 Na 1 C and 3 O
Counting Atoms: Practice
• Tell which elements are in the compound AND
how many atoms of each element there are:
1. NaHCO3
2. N4H3
Counting Atoms
• When there is a subscript written outside
parentheses in a chemical formula, the
subscript MULTIPLIES by all of the elements
inside of the parentheses.
(SO4)3 = 1 x 3 S = 3 S
4 x 3 O = 12 O
15 atoms total
Counting Atoms
• A coefficient is a number written in front of a
chemical symbol.
• The coefficient also MULTIPLIES by the element
and/or subscript.
Example 1: 4 H2O = 4 x 2 H = 8 H 12 atoms total
=4x1O=4
O
Example 2: 2 (NH4)3PO4 = 2x 1 N = 2 N
= 2 x 4 x 3 H = 24 H
=2x1P=2P
36 atoms total
=2x4O=8O
Reading Models of Formulas
Na
Cl
NaCl
H2O
Reading Models of Formulas
O
C
O
O
Ca
CaCO3
Drawing Models of Formulas
Na2Cl2
2H2O
Cl
Cl
Na
Na