Download 17.3 The periodic table

17.3 The periodic table
Warm up
 What is the atomic
number and the atomic
mass of Silicon?
 Calculate the number of
protons, electrons and
neutrons in the following
element if the atomic
number is 28.
 Is the atom of Si
considered neutral? Why?
Objectives
 Explain the composition of the
periodic table.
 Use the periodic table to obtain
information.
 Explain and distinguish between
metals, non – metals and metalloids.
Introduction
 Complete the following patterns:
 Each month, the moon seems to look at one of the
following phases:
This type of change is periodic “ repeated in
a pattern”
Organizing of the element
 In the late 1800, Dmitri Mendeleev
searched for a way to organize
elements.
 When he arranged all the elements
known at that time in order of
increasing atomic mass, he
discovered a pattern.
 Chemical properties in light elements
were repeated in heavier elements.
Because the pattern repeated, it is
now considered to be periodic.
Organizing of the element
 Later, Henri Moseley
established that each
elements has a unique atomic
number, which is how the
current periodic table is
organized.
 Today the arrangement of the
elements is called the periodic
table of elements.
 In the periodic table, nowadays,
elements are arranged according
to the increasing atomic number
and by changes in physical and
chemical properties.
Current periodic table
 The modern periodic table uses Moseley’s arrangement of elements.
The periodic law
 The periodic law states that when the elements are arranged by
increasing the atomic number, a periodic repetition of chemical
and physical properties of the elements are noticed.
Sort or group the following objects according to their properties.
The atom and the periodic table
 Elements in the periodic table are arranged in groups, or
families, and are numbered from 1 through 18.
 Elements in each group have similar properties.
 Example: gold, silver and copper
 If you looked at one atom of every element in a group
you would see…
 Each atom has the same number of electrons in it’s
outermost shell.
 An example… The group 2 atoms all have 2 electrons in
their outer shells
Be (Beryllium)
Atom
Mg (Magnesium) Atom
Why do elements in the same group
have similar properties?
 Do you know where electrons are located?
 Scientists have found that electrons within the
electron cloud have different amount of energy.
They placed electrons in energy levels around the
nucleus.
 The number of outer or “valence” electrons in an
atom effects the way an atom bonds.
 The way an atom bonds determines many properties
of the element.
 This is why elements within a group usually have
similar properties.
Maximum number of electrons in an energy level is
2n2 where n is the number of energy levels
Application
 How many electrons are found in:
1- first energy level
2- second energy level
3- third energy level
4- fourth energy level
Energy levels
 The energy levels where electrons are distributed
around the nucleus are named using numbers 1 to 7.
 What is the maximum number of electrons in energy
level: 1, 2, 3 & 4?
 A complete and stable outer energy level can contain a
maximum of 8 electrons
Rows on the table
 Electrons are distributed in energy levels around the
nucleus.
 Elements are arranged in rows in the periodic table.
 Each row of the periodic table specify the number of
energy level an atom has.
 The horizontal rows of the elements on the periodic
table are called periods.
 The element increase by one proton and one electron as
you go from left to right in the periodic table
 Which of the following has a stable outer energy level? Find
the group and the period of each of the following element.
Electron dot diagram
 Way to represents the number of electrons in the outer
energy level.
 Created by an American Chemist known as Lewis
 Also known as Lewis dot symbol
 Uses the symbol of the element and the valence
electrons (electrons of the outermost energy level)
Application
 Draw the Lewis dot diagram of the following elements:
Same
Group or same Period
 Elements on the same group have the same number of
electrons in the outermost energy level.
 Since all members of a group on the peridic table have
the same number of electrons in the outer energy level,
group members will undergo chemical reactions in the
same way.
 Elements on the same period or row on the periodic
table have the same number of energy levels.
Example: (H & He), Li & Be & B & C & N & O & F & Ne)
Regions of the periodic table
 The periodic Table is divided into several groups based
on the properties of different atoms.
Wrap up
 Use the periodic table to find the name, atomic number, symbols, the
average atomic mass , group, and the period for the first 20 elements
 Define the periodic law
 Compare and contrast the ways in which Mendeleev and Moseley
classify the elements in the periodic table
 Define groups and periods
 Draw electron dot diagrams
 Describe the general characteristics of metals, nonmetals, and
metalloids
 Indicate the energy levels where electrons are arranged.
 the maximum number of electron that each energy level can hold
(2n2), where n= number of energy level( n=1,2.3…., n=7)
Assignments
 Home work section review questions page:
524
 Quiz 2 in section 17.1: Structure of the
atom
17.2: Masses of the atom
9-08 on Wednesday, feb. 15, 2012
9-05, 9-06 & 9-07 on Thursday, Feb. 16, 2012