Material Properties

Material Properties

The structure of the atom

Learning Objectives

• Describe the model used for the structure of the atom

• Describe about the methods and discoveries of Rutherford

• Explain the detailed structure of the atom, using the atomic and mass numbers to construct a diagram of the structure of an atom

The structure of the atom

The word “atom” comes from Greek word that mean “cannot be split”.

Scientists have discovered that atoms are made up of even smaller particles as protons ,neutrons and electrons.

The protons and neutrons are closely together in the center of the atom (nucleus).

The electrons move around the nucleus.

The structure of the atom

In the late 1890s a British scientist called J.J.Thompson discovered the electron.

In the 1909 Ernest Rutherford (student of Thompson who is from New Zealand)  discovered the proton and in the 1911 discovered nucleus.

Rutherford had gold foil experiment.

In this experiment Rutherford fired fast moving particles smaller than an atom to at very thin gold foil.

The structure of the atom

Most of the particles passed straight through the foil.

Only a few of these particles (about 1 in 8000) were deflected in various directions.

This led Rutherford to have the idea that gold atoms  must be mostly empty space , with their particles packed into a dense nucleus at the center.

The structure of the atom

James Chadwick  worked with Rutherford and Thompson in 1932 proved that neutrons exist.

Their experiments and ideas have helped us to understand the structure of the atom.

The structure of the atom

The atoms of elements increase in mass from left to right and top to bottom in periodic table.

Each element has an atomic number.

Atomic number tells how many proton that element contain.

The atomic number increases by one with every element from left to right in periodic table.

The structure of the atom

Each element has a mass number.

Mass number tells how many protons and neutrons each atom in the element has in total.

Protons have a positive charge and electrons have negative charge .

An atom has no overall charge  because the number of proton is the same as the number of electrons.

The structure of the atom

A Danish scientist Niels Bohr first had the idea that electrons move in different shells around nucleus.

The electrons are arrange in electron shells or orbits around the nucleus.

This arrangement is known as electronic structure.

The structure of the atom

The first shell has only room for two electrons (duplet)

The second  and third shells each have room for eight electrons (octet) 

The arrangement of  electrons in an atom is often written as number,example 2,3 mean is in first shell 2 electrons and in second shell there are 3 electrons so the first shell always fill up before electrons go into the second shell.

Trends in group 1

-In periodic table vertical columns are known as group.

-The first group is known as the alkali metals.

-Lithium(Li) , sodium(Na) and potassium(K) are located in first group.

-These elements have some properties in common.

Trends in group 1

-The atomic number increases from top to bottom.

-The mass number also increases from top to bottom.

-These increasing numbers show that the size of the atom is increasing.

-Reactivity of first group elements is increase from top to bottom.

-From top to bottom number of shells is increasing by one.

Summary

-The elements in group 1 share some properties.

-The trend in group 1 is that the melting points and the boiling points decrease , as you go down the group.

-The elements in group 1 react more vigorously with water as you go down the group.

Trends in some other groups

Trends in group 7 (Halogens)

Trends in group 8 (Noble gases)

Trends in group 7

-This group is known as halogens.

-Fluorine(F) ,chlorine(Cl) and bromine(Br) are in this group.

-Fluorine and chlorine are gases at room temperature and bromine is liquid.

-Reactivity of group 7 is decreased from top to bottom.

-From top to bottom number of shells is increasing by one.

Trends in group 8

-This group is known as noble gases.

-All elements in group 8 are gases.

-Helium(He), neon(Ne), and argon(Ar) are in this group.

-Group 8 elements are inert and do not form compounds.

-From top to bottom number of shells is increasing by one.

Summary

-The elements in each group share some properties.

-The elements in 7 groups react less vigorously as you go down the group.

-The elements in group 8 have all their shells full and do not react to form compounds.