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. 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 2n 2 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

Same G roup or same P eriod 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 (2n 2 ), 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, , 9-06 & 9-07 on Thursday, Feb. 16, 2012