1. Lecture 80 – Lecture 81 – Lecture 82 The Periodic Table Ozgur Unal
NIS – PHYSICAL SCIENCE
Lecture 80 – Lecture 81 – Lecture 82
The Periodic Table
Ozgur Unal

2. The Periodic Table
The arrangement of the elements according to the increasing atomic number is called the periodic table.
Why is it called the periodic table?

3. Mendeleev’s Predictions
In the late 1800s, Dmitri Mendeleev searched for a
way to organize the known elements.
When he arranged all the elements in order of increasing atomic masses, he discovered a pattern.
Chemical properties found in lighter elements could be shown to repeat in heavier elements  periodicity
At the time of Mendeleev not all elements were known.
Mendeleev predicted the existence of some elements in his table  Example: Germanium, Scandium
Scientists later discovered these missing elements and found that their properties were extremely close that what Mendeleev had predicted.
Check out Table 4!!

4. Mendeleev’s Predictions

5. Moseley – Improving the Periodic Table
In 1913, Henry Moseley’s work led to the arrangement of elements based on their increasing atomic numbers instead of an arrangement based on atomic masses.
The current periodic table uses Moseley’s arrangement of the elements.
Who is Henry Moseley?

6. Metals, Nonmetals and Metalloids

7. The Atom and the Periodic Table
The vertical columns in the periodic table are called groups.
Groups in the periodic table are numbered from 1 to 18.
Elements in each group have similar chemical properties.
Example: Group 11 elements, Cu, Au and Ag are all shiny metals and good conductor electricity and heat.
What is responsible for the similar properties?

8. The Atom and the Periodic Table
Remember the electron cloud model..
Today we know that electrons within
the electron cloud have different amounts of energy.
There are different energy levels that electrons can occupy.
The closer the energy level to the
nucleus, the less energy it has.
Check out Figure 9!!

9. The Atom and the Periodic Table
The number of electrons in the outermost energy level in an atom determines the chemical properties.
Elements that are in the same group have the same number of electrons in their outermost energy level.
There are seven energy levels.
Each energy level can contain a certain maximum number of electrons.
1st level  2 electrons
2nd level  8 electrons
3rd level  18 electrons
4th level  32 electrons
A complete and stable outer
energy level will contain 8 electrons.

10. The Atom and the Periodic Table
The horizontal rows in the periodic table are called periods.
H  1 electron in the first energy level  Group 1 & Period 1
Li  2 electrons in the first energy level, 1 electron in the second energy level  Group 1 & Period 2
Mg  2 electrons in the first energy level, 8 electrons in the second energy level, 2 electrons in the third energy level  Group 2 & Period 3
O  2 electrons in the first energy level, 6 electrons in the second energy level  Group 16 & Period 2
Cl  2 electrons in the first energy level, 8 electrons in the second energy level, 17 electrons in the third energy level  Group 7 & Period 3

11. Electron Dot Diagrams
The chemical properties of an atom is determined by the number of electrons in the outermost energy level.
A very convenient way to represent atoms is the electron dot diagram, invented by G.N. Lewis.
An electron dot diagram uses the symbol of the element and dots to represent the electrons in the outermost energy level.
Check out Figure 11!!
Write down the electron dot diagram for Group 17 elements (aka halogens)
Group 1 elements can form compounds with Group 17 elements.
Example: NaCl
This is because the most stable outer energy level configuration is the one with 8 electrons.