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Charge

We have seen that every object has a property called mass. Another property that every object has is charge.

Just like mass, charge is very important in Chemistry. Every time we learn about a new particle in this course, its charge will be one of the key things we look at.

Charge is important because it is fundamental to many different aspects of Chemistry, including atomic structure, bonding, and chemical reactions.

Charge can be positive, negative or zero

When we learnt about mass, we saw that it is impossible for an object to have a negative mass. Almost all objects have a positive amount of mass - the only exceptions are a couple of types of particle that have zero mass.

Charge, on the other hand, can take any value: positive, negative or zero.

An object with a positive amount of charge is described as positively charged, an object with a negative amount of charge is described as negatively charged, and an object with zero charge is described as neutral.

Charge is measured in Coulombs

The units of charge which we will use in this course are Coulombs, which are abbreviated to a capital C. For example, negative twelve Coulombs would be written as -12C.

Because charge can be positive or negative, it is a good idea to always put a plus sign in front of positive charges. For example, ten Coulombs would be +10C. Although this plus sign is not necessary, it is helpful because it will remind you to always think about whether the charge is positive or negative.

If an object is neutral, then its charge is zero Coulombs, which is written as 0C (with no plus or minus sign).

Charged objects attract or repel each other

We have seen that mass causes objects to be affected by the force of gravity. Charge causes objects to be affect by a different force, called the electrostatic force.

Whenever two objects with a positive or negative charge are near each other, they both experience the electrostatic force. Neutral objects are not affected by the electrostatic force.

If one object is positive and the other one is negative then they are described as having opposite charges. If two objects with opposite charges are near each other, then each object will experience an electrostatic force pulling it towards the other one. In other words they experience forces of electrostatic attraction. This is summarised by saying that opposite charges attract.

On the left: a red box with a plus sign on it (for positive). On the right: a blue box with a minus sign on it (for negative). The two boxes have arrows pointing towards each other (to represent the attractive forces).

Oppositely charged objects are attracted towards each other by the electrostatic force.

If the objects are both positively charged or both negatively charged then they are described as having like charges (‘like’ means the same or similar). If this is the case, then each object will experience an electrostatic force pushing it away from the other one. In other words, they experience forces of electrostatic repulsion. This is summarised by saying that like charges repel.

Two positively charged objects being repelled away from each other.

Two positively charged objects repel each other. They experience forces of electrostatic repulsion pushing them away from each other.

Two negatively charged objects being repelled away from each other.

Two negatively charged objects repel each other. They experience forces of electrostatic repulsion pushing them away from each other.

The size of the electrostatic force depends on the amount of charge that two objects have and the distance between them. The more charge they have, the stronger the force is. The closer together they are, the stronger the force is.

Flashcards

Flashcards help you memorise information quickly. Copy each question onto its own flashcard and then write the answer on the other side. Testing yourself on these regularly will enable you to learn much more quickly than just reading and making notes.

1/5

What is charge?

2/5

What are the units of charge? What are they abbreviated to?

3/5

What are the possible values that charge can have?

4/5

What happens when two oppositely charged objects are near each other?

5/5

What happens when two like charged objects are near each other?

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