Atoms & Elements
•What is an atom?
An atom is the smallest particle of an
element that retains its identity in a
chemical reaction.
Word origin: atom comes from the Greek
word atomos meaning “ indivisible”
•Elements & Compounds
•
What would atoms of an element, mixture and
compound look like at a microscopic level?
•Subatomic Particles
•
The parts that make up an
atom!
• protons
• neutrons
• electrons
electron
proton
nucleus
neutron
•Subatomic Particles
Protons
•
Found in the
nucleus
•
Found in the
nucleus
•
Identifies the
element
•
Plays no role in
chemical behavior
•
•
#of protons =
specific element
Responsible for
chemical and
physical properties
Electrons
Neutrons
•
Purpose: to put
space between
protons
•
•
•
Spin around in set
regions outside of
nucleus
Most important in
chemical reactions
Farthest electron
away from nucleus
determines how
atoms chemical to
combine to one
another.
•Subatomic Particles
Name
Symbol
Charge
Relative Mass
Proton
p+
+1
1
Neutron
no
0
1
Electron
e-
-1
0 (1/1840)
How big is an atom?
Imagine the nucleus is the size of a marble
located in the middle of the football field,
the electron would be in the classroom the size of a period!
•Periodic Table
Greatest Cheat Sheet Ever!
•Periodic Table
Categories:
Metals
•
Rows: periods
•
•
7 periods
Columns: groups or families
•
18 Groups
•
1A: Alkali Metals
•
2A: Alkaline Earth Metals
•
7A: Halogens
•
8A: Noble gases
•
B Groups: Transition and Inner
Transition Metals
Nonmetals
Metalloids
(B, Si, Ge, As, Sb, Te, At)
•Periodic Table
14
Symbol
Si
Silicon
28.086
Atomic Mass
Atomic Number
Element name
•Important Numbers
• Atomic
•
Number
Counts the number of protons in an atom
within the nucleus
14
Si
Atomic Number
= # of protons
Silicon has 14 protons
•Atomic Number
•
State the number of protons for atoms of each of the
following:
• A.
Nitrogen
• B.
Potassium
• C.
Neon
•Atomic Number
•
State the number of protons for atoms of each of the
following:
• A.
•
• B.
•
• C.
•
Nitrogen
7 protons
Potassium
19 protons
Neon
10 protons
•Number of Electrons
• An
atom is neutral
• The
net charge is zero
• Number
• Atomic
of protons = Number of electrons
number = Number of electrons
• Remember:
proton = +1 electron = -1
•Number of Electrons
14 electrons
14
14 protons
Si
-14
+14
= 0 neutral
•Important Numbers
•
Mass Number
14
Si
Silicon
28.086
•
•
Atomic Mass
Counts the number of protons and neutrons in an
atom
OR
Determined by: the whole number closest to the
Atomic Mass
•Mass Number
•
Atomic Symbols
Show the mass number and atomic number
• Give the symbol of the element
•
Mass Number
Atomic Number
28
14
Si
silicon-28
•Determine the Mass Numbers
4
Be
27
Co
10
Ne
9.0122
58.933
20.179
9
59
20
•Write the Symbol and Name for
each
4
Be
9.0122
9
Be
4
beryllium-9
27
Co
10
Ne
58.933
20.179
59
Co
27
20
Ne
10
cobalt-59
neon-20
•Mass Number
•
The total number of particles in the nucleus
•
•
# of protons + # of neutrons
To determine the number of neutrons
•
Mass number – Atomic number = # of neutrons
16
8
O
31
15
P
65
30
Zn
#p
8p+
15p+
30p+
#n
8no
16no
35no
8e-
15e-
30e-
#e
•Isotopes
•
•
The
identifies the element, but
an element may have atoms with several
different
.
Most elements consist of several different
isotopes
•
Same number of protons , Different number of
neutrons
•Isotopes of Hydrogen
•
Naturally occurring hydrogen consists of 3 isotopes,
protium (H-1), deuterium (H-2), and tritium (H-3).
State the number of protons, neutrons, and electrons.
1
1
#p
#n
H
1
0
#e
1
2
1
H
3
1
H
1
1
1
2
1
1
•An atom of Calcium (Ca-40)
•
A.
Number of protons
•
B.
number of neutrons
•
C. What is the mass number of a calcium isotope
with 19 neutrons?
•Atomic Mass
•
This is NOT a whole number
•
A given element can have atoms with several
different mass numbers.
•
Average mass of the atoms with all possible
mass numbers
•
We will calculate later 
•Write the atomic symbol
• A.
11p+, 12no, 11e-
• B.
17p+, 20no, 17e-
• C.
47p+, 60no, 47e-
•Write the atomic symbol
• A.
11p+, 12no, 11e-
23
11 Na
• B.
17p+,
37
17
• C.
47p+, 60no, 47e-
20no,
17e-
Cl
107
47 Ag
•Ions
•
•
•
Atoms with a charge (positive or negative)
Remember atoms are neutral, therefore if an atom
has a charge we call it an ion.
Ions- Atoms which gain or lose an electron
atom
#p
11
#e
11
ion
11
10
Na1+
atom
#p
17
#e
17
ion
17
18
Cl1-
Why do the
electrons change?
•Why?
• If
protons change…new______?________
• If
neutrons change…new______?______
• If
electrons change….new _____?______
•Why?
• If
protons change…new element
• If
neutrons change…new isotope
• If
electrons change….new ion
•Ions
#p
atom
12
ion
12
#e
12
10
#p
atom
8
ion
8
#e
8
10
Mg 2+
O 2-
•Complete Atomic Symbol
combines isotopes and ions
27
Al
13
•
•
3+
What does each represent?
How many of what subatomic particles does each
represent?
•Complete Atomic Symbol
combines isotopes and ions
Mass number
27
Al
13
3+
Ionic charge
Atomic number
13p+
10e-
14no
•How many protons, neutrons, &
electrons?
14
7
N3-
7p+
7no
10e-
32
15
P3-
15p+
17no
18e-
65
30
Zn2+
30p+
35no
28e-
•Atomic Mass
Coming back to this…
Atomic mass is the weighted
of all the atomic masses of the isotopes of
that atom.
So we involved all the different forms of
ATOMS of an element (ions not an issue
here) and how frequent they are
•Average Atomic Mass cont.
•
To find the Average Atomic Mass (generally
referred to as the atomic mass of an element)
we need to use two things
•
•
•
The mass of the isotope
Multiplied by its frequency
Then we add all the forms up.
•Example of Average Atomic Mass
Cl-35 is about 75.5 % and Cl-37 about
24.5% of natural chlorine.
35 x 75.5 = 26.4
100
35.5
37 x 24.5 = 9.07
100
• Rubidium
has two common isotopes,
Rb-85 and Rb-87. If the abundance of
Rb-85 is 72.2% and the abundance of
Rb-87 is 27.8%, what is the average
atomic mass or rubidium?