3.1 Electron Theory

Question 1

In nature, atoms and molecules are electrically neutral. Friction can change this by allowing the transfer of charges from one body to another, without altering the appearance of either

Answer 1

Protons
Protons are positively charged particles in the nucleus.

Neutrons
Neutrons are neutral particles in the nucleus.

Question 2

Electrons
Electrons are negatively charged particles travelling in various orbits (shells) around the atomic nucleus. They are attracted to the positively charged protons, which prevents the electrons from moving away from the nucleus.

Question 3

The charge of a single electron is:

Answer 3

-1.602 x 10^(-19) Coulombs

Question 4

The charge of a single proton is:

Answer 4

+ 1.602 x 10^(-19) Coulombs

Question 5

The magnitude of this quantity is known as the elementary charge, which has the symbol e:

Answer 5

e = 1.602 x 10^(-19) Coulombs

Question 6

The elementary charge is a fundamental physical constant that represents the electric charge of a single proton or electron

Question 7

Protons and neutrons make up the mass of an atom; electrons have almost no mass.

Answer 7

An atom is electrically neutral if it has an equal number of protons and electrons. Consequently, the atom has no electrical charge.

Question 8

If an atom has more electrons than protons, its charge is negative.

Answer 8

If there are fewer electrons than protons, the atom’s charge is positive. Positively or negatively charged atoms are called ions. A charged atom is said to be ionised.

Question 9

Molecules

A molecule is an electrically neutral group of two or more atoms held together by chemical bonds. A charged molecule is also called an ion.

Answer 9

For example, the molecule of the element oxygen is made up of two oxygen atoms (O2), whereas the molecule of water is made up of two hydrogen atoms and one oxygen atom (H2O). In a pure compound, each molecule contains the same number of atoms of each element. It follows therefore that elements can only combine to form compounds in certain fixed proportions.

Question 10

Ions

In some materials the outer electrons can easily be detached from the atom, requiring only a small amount of external energy to overcome the attraction of the nucleus. Sources of such energy may be heat, light, electrostatic fields, etc.

Question 11

what is a positive ion

Answer 11

Positive Ion: The electron once detached from the atom is able to move around the structure of the material and is called a “Free Electron”. The atom which has lost the electron has now gained an overall positive charge and is therefore called a “Positive Ion”.

Question 12

what is a negative ion

Answer 12

Negative Ion: When an atom gains an electron in its outer orbit it becomes overall negatively charged and is called a “Negative Ion”

Ions can be created by physical or chemical means, e.g., by dissolving a salt in water, or, passing a direct current through a conducting solution, which dissolves the anode via ionisation.

Question 13

Compounds

When two or more elements are combined chemically, the new substance is called a compound.

Question 14

There are four main types of compounds, depending on how the constituent atoms are held together. For this module, we will only cover the following two:

Answer 14

Molecules held together by covalent bonds.

Ionic compounds held together by ionic bonds.

(research ionic and covalent bonds)

Question 15

In a metal, the atoms are closely packed and form a giant structure with a regular pattern, which is called a crystal lattice. The outer shells of all the metal atoms in the crystal overlap, allowing the electrons in these shells to move freely through the lattice. It is helpful to think of these electrons as forming a fluid within the crystal, like a “sea of free electrons”

Answer 15

This high electron mobility makes metals good conductors of both electricity and heat.

Generally, good conductors contain atoms having less than four electrons in the outer shell (valence orbit).

Examples of strongly conductive metals include copper, aluminium, and silver

Question 16

A semiconductor may be defined as a material whose conductivity is somewhere between that of a good conductor and a good insulator. The conductivity of a semiconductor can be affected by temperature, doping (adding foreign atoms), or by light – this makes semiconductors very useful in many applications. Semiconductors are better conductors at higher temperatures, unlike metals which are poorer conductors at higher temperatures.

Answer 16

Semiconductors have a small number of free electrons compared to metals. If we assume that metals, on average, have one free electron per atom, then semiconductors might have one free electron per million atoms, at room temperature.

Question 17

Generally, semiconductors contain atoms with four electrons in their outer shell (valence orbit).

Semiconductor elements sit between the metals and non-metals in the periodic table. Some compounds are also important semiconductors.

Answer 17

Examples of semiconductors include silicon and germanium.

Question 18

Insulators are also known as non-conductors.

In the structure of insulators, electrons are tightly connected to the atoms or molecules, which prevents them from breaking away. The lack of any free electrons prevents the conduction of electricity.

Answer 18

Generally, good insulators contain atoms having more than four electrons in their outer shell (valence orbit).

Examples of good insulators include mica and porcelain

Question 19

what are the respective names for a positively and negativley charged ion

Answer 19

Cation , Anion