The periodic table organizes all of the known elements according to
their chemical properties.
They can be grouped into three major cateogories: metals, non-metals
and metalloids.
staircase
line
• Metals have a shiny, metallic lustre.
• Metals are good conductors of heat and
electricity.
• Metals are malleable.
For example, tin (Sn) can be hammered into
very thin sheets without breaking
tin
• Metals are ductile.
They can be drawn into long wires.
• All metals are solids at room
temperature, except for mercury (Hg),
which is a liquid.
silver
Typical metallic solid and it’s
“sea of electrons:”
• Nonmetals are dull.
• Nonmetals do not conduct heat well
and do not conduct electric currents.
• Nonmetals are brittle.
• Nonmetals are solid, liquid or gas at
room temperature.
sulphur
iodine
arsenic
• Metalloids have characteristics of
both metals and nonmetals.
• Metalloids are often brittle solids.
• Metalloids conduct electricity, but
not as well as metals.
boron
silicon
The first periodic table was invented
by Dimitri Mendeleev in 1872.
Dimitri Mendeleev
(1834-1907)
18 groups or families
7
periods
alkali metals
noble gases
alkaline earth metals
halogens
All atoms are made up of three subatomic particles:
1) proton
2) neutron
3) electron
symbol:
p

0
symbol:
n
symbol:
e
Protons and neutrons are
located in the nucleus.
The mass of a proton or neutron is about
1800 times the mass of an electron.
Electrons are found in energy
levels around the nucleus.
The atomic number of an element indicates the number of protons
it has.
An atom of any element is electrically neutral, so the number of
positive charges (protons) is equal to the number of negative
charges (electrons).
State the number of protons for
atoms of each of the following:
1) sodium: 11
2) carbon:
6
3) chlorine: 17
The elements on the
periodic table are
organized by increasing
atomic number!
Atoms of the same element have the same number of
protons, but can have different numbers of neutrons.
Isotopes are atoms of the same element that
contain different numbers of neutrons.
To differentiate between isotopes of a given element, we use a number
called the mass number.
The mass number is a number equal to the total number of protons
and neutrons in the nucleus of an atom.
mass number
Isotope notation:
A
Z
X
element symbol
atomic number
Three naturally occurring isotopes of carbon:
12
6
C
13
6
C
14
6
C
The bottom number is sometimes not written because you
can determine the atomic number from the symbol.
Any sample of an element found in nature is a mixture of different
isotopes. Each isotope will occur in different proportions, usually given
as a percentage.
For example:
Each of these isotopes contains 50 protons.
Isotopes of Tin
Sn-112
0.97%
Sn-122
4.63%
Sn-124
5.79%
Sn-114
0.65%
Sn-115
0.34%
Sn-116
14.53%
Sn-117
7.68%
Sn-120
32.59%
Sn-119
8.59%
Sn-118
24.23%
The atomic mass of an element that is listed on the periodic
table is called the atomic molar mass.
This value is calculated as the average mass of all of the isotopes of
an element, taking the percent abundance into account.
Isotopes of Tin
Sn-112
0.97%
Sn-122
4.63%
Sn-124
5.79%
Sn-114
0.65%
Sn-115
0.34%
Sn-116
14.53%
Sn-117
7.68%
Sn-120
32.59%
Sn-119
8.59%
Sn-118
24.23%
Since the mass of individual atoms is so small, it is not convenient to
use a unit like grams (g).
Instead, we use the atomic mass unit (amu).
An atom of carbon-12 was assigned an
exact mass of 12.00 amu.
Then the relative masses of all other
atoms is determined by comparing each
to the mass of an atom of carbon-12.
For example, an atom twice as heavy has a mass of 24.00 amu, and an
atom half as heavy has a mass of 6.00 amu.
An atom has 14 protons and 20 neutrons.
1) Its atomic number is :
A) 14
B) 16
C) 34
2) Its mass number is :
A) 14
3) The element is:
A) Si
B) 16
C) 34
B) Ca
C) Se
4) Another isotope of this element is :
A)
34
16
X
B)
34
14
X
C)
36
14
X
Write the atomic symbols for atoms with the following:
A. 8
p+
,8
n0 ,
8
e-
B. 17 p+ , 20 n0 , 17 e-
C. 47
p+
, 60
n0 ,
47
e-
16
8
O
37
17
Cl
107
47
Ag
An atom of zinc has a mass number of 65.
1) The number of protons in the zinc atom:
A) 30
B) 60
C) 65
2) The number of neutrons in the zinc atom:
A) 30
B) 35
C) 65
3) The mass number of a zinc atom with 37 neutrons is:
A) 37
B) 65
C) 67
 read pages 28 – 34 (up to Formation of Ions)
 Worksheets:
 Line Master 4 - Atomic Mass and Mass Number
 Line Master 5 - Atoms, Protons, and Electrons
A model that shows the placement of electrons around the nucleus of an
atom or ion.
Energy levels contain electrons that are
similar in energy and distance from the
nucleus.
Low energy electrons are closest to
the nucleus.
# p+
# n0
Each level can hold a certain
maximum number of electrons
before it is full:
Level
Max. # of
Electrons
1
2
3
2
8
8
All the elements in a group have the same electron configuration in
their outermost shells. Electrons in the outer shell that is not full are
called valence electrons.
Noble gases have no valence electrons, their
outer shell is full. That is why they are so stable
and non-reactive.
The period number (horizontal row) that an element is in is the
same as the number of energy levels the atom has.
Draw energy level diagrams for the following isotopes:
a)
24
12
Mg
2 e2 e-
OR:
8 e-
2 e12 p+
12 n0
2 e12 p+
12 n0
8 e-
For neutral atoms,
the number of
protons equals the
number of electrons.
Excellent!!
b)
20
9
F
7
c)
e-
32
P
5 e8 e-
2 e-
2 e-
p+
9
11 n0
15 p+
17 n0
Given the diagram, write the symbol.
d)
4
e)
e-
3 e-
8 e-
2 e-
2 e-
5 p+
7 n0
14 p+
12 n0
26
14
Si
12
5
B
Recall that an atom of any element is neutral, so the number of protons
equals the number of electrons.
An ion is a an atom (or a group of atoms) that has a positive or
negative electric charge.
The formation of an ion is called ionization, and is the result of an atom
either gaining or losing electrons.
The number of
protons only changes
in nuclear reactions,
never in the
formation of ions.
Cations are positively charged ions.
They are formed when a metal atom loses valence
electrons (electrons in the outermost energy level).
Ant-ion?
Anions are negatively charged ions.
They are formed when a non-metal atom
accepts electrons into its outer energy level.
The octet rule says that atoms tend to gain, lose
or share electrons so as to have eight electrons
in their outer electron shell.
Atoms gain or lose electrons so that they have the same number of
electrons as the nearest noble gas.
Some metal atoms, depending on the nature of the chemical reaction,
can form stable ions with more than one charge.
For example copper atoms will lose either one or two electrons.
Cu
+
Cu 2+
These elements are called multivalent, and the first charge given on the
periodic table is the most common.
Symbol
Atomic #
Protons
Electrons
Neutrons
Mass #
Charge
Ag
47
47
47
61
108
0
Br
35
35
35
42
77
0
Pb
82
82
82
123
205
0
O2-
8
8
10
8
16
-2
Cu
29
29
29
31
60
0
N3-
7
7
10
7
14
-3
 read pages 34 – 38 (except p. 37)
 A2.1 Check and Reflect
page 39 #’s 1 – 12