Name: ____________________
Period: __________
WHAT., IS A ,FORMULA?
formula:
the short way of writing
a compound
73
AIM
What is a formula?
13
Each element has its chemical symbol. Each compound"
has its chemical formula. The formula tells us two important
things about the compound. It tells us which elements there
are in a molecule. A formula also tells us how many atoms
there are of each element.
.,i,.
»:
The formula for table salt is NaC}.
Na is the symbol for sodium.
chlorine
CI is the symbol for chlorine.
One molecule of NaCl has a total of two atoms. One of
the atoms is sodium (Na). The other atom is chlorine (CI).
Chart I page 75 has more examples.
Sometimes a symbol has a small number written next to
it. This number tells us the number of atoms there are of that
element.
oxygen
The formula for water is H20.
H is the symbol fat hydrogen.
o is the symbol for oxygen.
H2 means two atoms of hydrogen.
q,;fneans,,o,-ne
.atom of oxygen.
'I," .•;':~~
.
•
.•.•
-':.'~" .."I
•',\ ' " . '_
!1ydtogen
:.>
'.' One,molecule ofH2(); then, has a total of three atoms. "
Two of the atoms are hydrogen. One atom is oxygen.
,-
"f
,,-
Chart.Il has more examples.
.
,Th~ formula for a>(jompound is always the same. A
change .inthe formula means that a new substance was formed.
It is helpfUl to leara, recognize some chemical symbols. But if you see one you don't know, you can always look
it up in a dictionary, an encyclopedia.',or a chemistry book.
to
NAME
74
~
~
~~~~--------~-~-------------
I.
SOME COMMON MOLECULES
-·~----~--l
I
."!
HgO
.--··'~--·---~------1-----------------,----------~-~-----_____::_I
I
Number of
I
I
Total Number of
I
Name--1 Elements_J_E:_~~:~~J~~:~e~~e_J
'I
I
~}
mercury (Hg)
oxygen (0)
I mercuric oxide
I
2
oxygen
-~-----~--..
-r ----~-r-~----'------~----I
potassium
chloride
potassium
r-------~--~-~----
-r------
I
II
NaOH
--- -
sodium
hydroxide
(lye)
~}
potassium (K)
chlorine (CI)
-
chlorine
-1--------------I
2
~-....
~I
sodium (Na)
oxygen (0)
hydrogen (H)
·~
CrJ
n
II
3
oxygen
~
SodiU~
""
hydrogen
75
II.
---------------1--- -------Number
Name
of
Atoms of
Each Element
Elements
---_.-._._,
iron oxide
(rust)
.
__ ._.-._-----
Total Number of
Atoms in
One Molecule
iron (Fe)
oxygen (0)
5
iron
iron
oxygen
oxygen
sulfuric acid
•
hydrogen (H)
sulfur (8)
oxygen (0)
7
hydrogen
baking soda
sodium (Na)
hydrogen (H)
carbon (C)
oxygen (0)
i}
carbon
I
sodium
hydrogen
oxygen
--------------------------_------------
NAME
76
~ __
:___------------------
T
I
6
CHOOSE
Choose the word that completes each sentence best.
ONE
1. A molecule is made up of
_
atoms, oxygen
2.
A single molecule has at least
_
atoms.
one. two
3.
The atoms of a molecule come from two or more _,,--
;--
elements. compounds
4.
There are
-:---_
elements than compounds.
more, fewer
5.
Molecules are _---:-__
.
than atoms.
larger, smaller
The formula for starch is C6H100~.
This stands for one molecule of starch.
Answer these questions about the starch molecule.
6.
Starch is made up of
~_.
elements.
one, two, three
7.
O.
The number of different kinds of atoms in starch is __
One molecule
of starch has
_----,-
:-----:-~---
three, billions
atoms of hydrogen.
two, six, ten
9. The total number of atoms in one molecule of starch is
10. The number of molecules in a teaspoon of starch is
---=---:-:--:c::---::-c:--6, 10, 16, 21
--------,-,-;-:c,---
twenty-one, billions
77
The chart below asks for some information about certain moleCOMPLETE
cules.
The first molecule, magnesium oxide, is done as an
THE CHART
example. Try to complete the chart by filling in the missing
information. You may use the list of elements and their symbols.
--------------------T----------- ---------1
r-------
Number
of
: 1.
MgO
magnesium oxide
1-2.- so~---tUl~r
3.
NH3
magnesiu
2
-r- - -
::Oxide
-------------l---
I
Names
of the
Number of Total Number
Atoms of
of Atoms In
1
1
1
oxygen -
1
2
--------
----+- --------- - --------+--
ammonia
•• ---H,CO,-- carbonic acid
I
(soda water)
L
_
I
I
5. C12H220tltable sugar
L------- -------!
I
6.
MgS04
i
r
'I"
7~~~ao:
8.
H20Z
-- ~1~~\um-~ydrOXide
hydrogen
peroxide
~------------1I
! 9. Fe203
i
i
1-------------------- --I
'"10.
------------------
iron oxide
(rust)
NaHC03 sodium bicarbonate
(baking soda)
_ __J_________
L_____________
NAME
78
l
-------------_
~________
_
_
_
MATCHING
Match the two lists. Writethe correct letter on the line next to
each number.
a) two or more different kinds of atoms
linked together
1-
CaF2
2.
HF
3.
HaPOa
4.
formula
5.
atoms in each molecule
b)
7
c)
contains one kind of atom
compound
d)
3
6.
element
e)
2 atoms in each molecule
7.
symbol
f)
short way of writing an element
g)
short way of writing a compound
atoms in each molecule
A VERY SPECIAL MOLECULE
Some molecules have thousands of atoms.
For example, the formula for one of the
substances in blood is
Try to answer these questions about this
large molecule.
1. How many atoms are there in just one molecule of this substance?
2.
How many atoms of each of the following elements are in one molecule?
carbon
hydrogen
oxygen
_
nitrogen
sulfur
----c--.--~
_
iron
~
_
79
TRUE OR
Write T on the line next to' the number if the sentence is
FALSE true. Write F if the sentence is false.
1.
Molecules are made of atoms.
2.
A molecule must have at least two atoms.
3.
A molecule has billions of atoms.
4.
You can tell how many atoms in a molecule by looking at the formula.
5.
A compound can have more than one formula.
REACHING
OUT
N~~E
80
The formula for water is H20.
The formula for hydrogen peroxide is H202•
What would happen if hydrogen peroxide were to lose one
oxygen atom?
___