Activity #3: Atoms & Elements
1
Vocabulary
 Atom
 Molecule
 Electron
 Nucleus
 Element
 Matter
 Proton
 Neutron
 Atomic Number
 Mass Number
 Atomic Symbol
 Periodic Table
 Neutral
 Chemical Formula
 Structural Formula
 Coefficient
 Subscript
2
Atoms
The basic units of
matter
Incredibly small
Placed side by side,
100 million atoms
would make a row
only about 1
centimeter long—
about the width of
your little finger!
3
What are Atoms made of?
Made of particles called
protons, neutrons, and
electrons.
Protons: positive (+)
charge
Electrons: negative (-)
charge
Neutrons: neutral (no
charge)
Normally have equal
numbers of electrons and
protons, making them
neutral
4
Elements
Pure substances made of
only one type of atom
Listed in the periodic table
of elements
Arranged in order of their
atomic numbers
An atom is the smallest
unit of an element that
has the properties of that
element
5
Atomic Number & Mass Number
Atomic number: the
number of protons
Typically the same
as the number of
electrons
Mass number: the
number of protons
plus the number of
neutrons
6
Example: Carbon
7
Practice
Element
Symbol
Atomic #
Mass #
Helium
He
2
4
Magnesium
Mg
12
Zinc
Zn
30
Bromine
Br
Aluminum
Al
# of Protons
# of
Neutrons
# of
Electrons
2
12
65
35
80
45
13
8
14
35
Important Elements for Biology
 Five most abundant
elements in living
things are:
1. Hydrogen – 10%
2. Oxygen – 65%
3. Nitrogen – 4%
4. Carbon – 19%
5. Phosphorus – 1%
O
C
H
9
N P
Molecules, Compounds, &
Chemical Formulas
Molecule: made when 2 or more of any atom are
joined together
Ex: O2, H2O
Compound: a substance formed by the
combination of two or more different elements
Ex: H2O, C6H12O6
All compounds are molecules, but NOT all
molecules are compounds
Chemical Formula- written shorthand showing the
composition of a compound
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Chemical Formulas
 Coefficient: tells how many
molecules of that substance
 Large number BEFORE the
formula
 Subscript: goes with the
element symbol preceding the
number; tells how many atoms
of that element within one
molecule of the substance
 Small number WITHIN the
formula
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Examples
Carbon – 1
Hydrogen - 4
Hydrogen – 12
Oxygen - 6
6
Carbon - 1
Oxygen - 2
Nitrogen - 1
Hydrogen - 3
12
Practice
 Example 2: 6CO2




What is the coefficient? _______
6
What is carbon’s subscript? ________
1
What is oxygen’s subscript? ________
2
How many molecules of this compound are
represented by this formula? _________
6
 How many atoms TOTAL are present in this
molecule?
______
18
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Structural formulas
 Drawing shows:
 types of elements in
the molecule
 number of atoms of
each element
 arrangement of atoms
and location of
covalent bonds.
 Shows the two
dimensional shape of
the molecule
water
14
glucose