Electric Charge and Ionic Bonds

atom.gif (1130 bytes) Electric Charge and Ionic Bonds

Protons have a POSITIVE charge

Electrons have a NEGATIVE charge

Neutrons are electrically NEUTRAL - they have no charge.

In normal atoms the number of Protons equals the number of electrons. This means that the positive and negative charges cancel each other out. When an atom donates, or accepts and electron during chemical bonding the charges are unbalanced. If an atom accepts one electron it is said to have a charge of minus 1 (-1). The atom that donated the electron will now have one more proton than electrons is said to have a charge of plus 1 (+1). Charged atoms are called ions.

The number of electrons an element donates, or accepts during chemical reactions is called its valency. Sodium, for example has a valency of +1. This means that it will donate one electron, resulting in the atom having 11 Protons, but only 10 electrons. Chlorine is said to have a valency of -1. This means that it will accept one electron, resulting it the atom having 17 Protons and 18 electrons.

In the examples below an atom such as Sodium which donates (gives away) one electron will be represented as a circle with an arrow head. An atom such as Chlorine which accepts an electron will be represented as a circle with a 'hole' for an arrow head.

Sodium has one electron to donate to become stable. Chlorine will accept one electron to become stable. A bond formed when atoms donate and accept electrons and are then attracted together by opposite electric charges are called ionic bonds.

The animation below represents what happens between Sodium and Chlorine ...

reaction.gif (4129 bytes)

In this animation, one electron leaves the Sodium atom and is accepted by the Chlorine atom. The positively charged Sodium ion is now attracted to the negatively charged Chlorine ion. The ions bond together forming Sodium Chloride (Table Salt).

The table below summarises valencies for the common elements:

valencytable.gif (5585 bytes)

NOTE: The valencies of the elements in the centre of the Periodic Table of Elements are a little confusing at this stage. They follow a quite logical pattern, but it is best to leave them until you do further studies in Chemistry.

Electric Charge and Ionic Bonds - QUIZ

Your Name and School -

Do you Certify the answers below to be all your own work? -

1. What are the three states of electric charge on atomic particles? -

2. What does the "valency" of an element tell us about the element?-

3. Briefly describe what happens when an atom of Potassium combines with an atom of Bromine. -

4. What are the valencies of: Calcium, Iodine, Oxygen, Sulphur and Carbon? -

5. How many atoms of Bromine will combine with one atom of Aluminium? -

6. What is the valency of an atom with a Mass Number of 15 and an Atomic Number of 7? -

7. What is the valency of an element with four electrons in its outer shell? Explain. -

8. What is the URL of a Web page containing information about Valency (apart from this one)?

Feedback, comments, questions -

(Make sure your NAME and SCHOOL are included.)

This form will be emailed to a 'marker'. You will receive feedback shortly. Satisfactory performance on this and other Quizzes is required for the granting of a "Completion Certificate" for this Course.