Download The Periodic Table

Atomic Theory
and the Periodic Table
Atomic Theory
All matter is made up of tiny particles called atoms
An atom is the smallest part of an element
that has all the element’s properties
 Atoms are not the smallest particles of
matter
 Subatomic particles combine together
to form atoms
 Protons
 Electrons
 Neutrons
 Protons have a charge of +1
 Electrons have a charge of -1
 Neutrons have a charge of 0 (neutral)
 The mass of protons and neutrons is
almost 2000 times greater than the
mass of an electrons
 Protons and neutrons form
the core of an atom, called the
nucleus
 The number of protons and
neutrons add together to give
the mass of the atom – each is
designated a mass of 1 amu
An atom isthe
smallest the
partnucleus
of an are
element
Surrounding
a series
cloud
like energy
levelsproperties
called shells
that of
has
all the
element’s
or orbitals
 These shells are occupied by
electrons
 Electrons are very light (approx. 0
amu)
The electron cloud is 10,000 times
larger than the nucleus
Imagine the nucleus
to be the size of a
golf ball. Then on
this scale the first
electron shell would
be about one
kilometer from the
golf ball, the second
shell about four
kilometers, the third
nine kilometers etc.
Electrons surround the nucleus in shells
Each shell has a specific energy level
The innermost shell holds 2 electrons
The next two shells holds 8 electrons
The outermost shell is called the
valence shell
The electrons in the valence shell are
called valence electrons
When the number of electrons equals
the number of protons, the atom is
neutral (no charge)
When there are more electrons (-) than
protons (+) the charge is negative
When there are less electrons (-) than
protons (+) the charge is positive
Ions
A Bohr-Rutherford diagram of
an atom shows the arrangement
and number of electrons in each
shell.
N
7p
7n
S
Cl
16p
16n
17p
18n
Let’s look at an example…
Sulphur
atomic
number
16
S
sulphur
32.07
Atomic Number:
ion charge = # of protons
= # of electrons
2(in neutral atom)
= 16
Atomic Mass:
= # of protons + # of neutrons
32 = 16 + # of neutrons
atomic mass # of neutrons = 16
Sulphur
Bohr-Rutherford Diagram:
S
32.07
16 p
16 n
Electrons pair up if
more than 4
2-
sulphur
Remember: the first shell
holds 2 e’s, the next two
shells hold 8 e’s each
Electrons drawn as far
apart as possible
16
Sulphur
Bohr Diagram:
first shell:
2 electrons
second shell:
8 electrons
Atomic number
= 16
16 p
16 n
third shell:
6 electrons
total:
16 electrons
In a sulphur atom, the valence shell has 6 electrons
The Periodic Table
of Elements
Periodic Table
The Periodic Table
 Elements are arranged in increasing order of
atomic number
 The atomic number tells the number of protons in
the atom.
 The horizontal rows of the periodic table are
called periods
 The vertical columns are called families or groups
 Elements in the same family have similar chemical
and physical properties
Periodic Table
Metals
 Metals are on the left and in the centre
of the periodic table
 Metals have the following properties:
 Conduct heat and electricity
 Malleable and ductile
 Shiny, most are silver
 Solid at room temperature (except mercury)
Metals
Non-Metals
 Non-Metals are on the right side of the
periodic table
 Non-Metals have the following properties:
 Poor conductors of heat and electricity
 Usually solid or gas at room temperature (only
Bromine is a liquid)
 Brittle
 Dull
Non-Metals
Metalloids
 Metals are separated from non-metals by a
staircase of elements called metalloids
 Metalloids have a blend of properties
between metals and non-metals
Tellurium
Silicon
Metalloids
Chemical Families
Chemical Families
Alkali Metals (Group 1)
 soft, silver-grey metals
 Reacts easily with water
Alkaline Earth Metals (Group 2)
 silver-grey metals
 harder and less reactive than
group 1 metals
Chemical Families
Halogens (Group 17)
 coloured non-metals
 very reactive
Noble Gases (Group 18)
 Colourless non-metals
 odourless
 very unreactive (does not
combine easily with other atoms)
Chemical Families
• All elements in the same family (or
group) have the same number of
valence electrons
Alkali Metals have 1 valence electron