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 elementLater, 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 tableThe modern periodic table uses Moseley’s arrangement of elements.

The periodic lawThe 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 tableElements 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)

AtomMg (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:

Carbon – sodium – sulfur – neon – hydrogen – calcium – magnesium – chlorine – oxygen – boron – beryllium – lithium – potassium – nitrogen – fluorine - phosphorous – silicon- Aluminum – helium and Argon

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 tableThe 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