Electrical Nature of Matter Grade Nine Science

Sections from Book 9.1 Electrostatics 9.2 Law of Electric Charges

Question to Ponder What happens when you rub a balloon against your hair? Does this action create electric charges? No! The electric charges were already there? Remember, all matter is composed of atoms and all atoms contain charges. Therefore, all matter contains electric charges.

What happens when you rub the balloon against your hair? Both items have negative and positive charges. In fact, both items are said to be neutral since the number of positive charges equals the number of negative charges. Since the balloon and your hair are comprised of two different materials one item attracts the positive charges and the other attracts the negative charges. Now each item is said to be charged.

Electrostatics: study of static electric charge. Most people are familiar with the shock associated with walking across a carpet and grabbing a doorknob. This shock is the result of static electricity. As you walk across the carpet, your body and the carpet exchange charges. Your body becomes charged but the charge does not move, it stays where the rubbing occurred. The charge is waiting for a chance to attract a neutral or opposite charge from another object. This is a result of “The Law of Electric Charges”

The Law of Electric Charges Like charges repel one another, and unlike charges attract one another. To determine whether an object is charged and, if it is charged, whether the charge is positive or negative, you must observe the object being repelled by an object with a known charge. Charged objects will attract both neutral objects and objects with opposite charges. On the other hand, charged objects will only repel objects with like charges.

The Law of Electric Charges states: Two objects with like charges, whether positive or negative, always repel one another. When a positive object is brought near a negative, the objects attract, “OPPOSITES ATTRACT”. ? - ? AttractionRepulsion

A Model for the Electrical Nature of Matter Scientists believe that all matter is made up of atoms containing particles that possess electric charges. Two scientists developed a model to help us visualize these particles. Actually, the first scientist, Rutherford, proposed the model and the second scientist, Bohr, refined it.

A Model for the Electrical Nature of Matter The Bohr-Rutherford model helps us understand how matter is structured and how it behaves. The main ideas of this model are presented on the next couple of slides.

A Model for the Electrical Nature of Matter 1.All matter is made up of particles called atoms. 2.At the centre of each atom is a nucleus, with two kinds of particles: the positively charged proton and the uncharged neutron. Protons do not move from the nucleus when an atom becomes charged.

A Model for the Electrical Nature of Matter 3.A cloud of negatively charged particles called electrons surrounds the nucleus. When atoms become charged, only the electrons move from atom to atom. 4.Like charges repel each other; unlike charges attract each other. 5.Some elements have a weaker attraction for its electrons than others and the electrons are able to move freely from atom to atom. A good example is copper

A Model for the Electrical Nature of Matter 6.A single atom is always electrically neutral. 7.If an atom gains an extra electron, the net charge on the atom is negative and it is called a negative ion. If an atom loses an electron, the net charge on the atom is positive and it is called a positive ion.

Negative Ions If an atom gains an extra e-, the net charge on the atom is negative, and it is called a negative ion. 6 protons (6+)6+ 6 electrons (6-)7- Neutral 0 (no charge)1- (-ion)

Positive Ions If an atom loses an extra e-, the net charge on the atom is positive, and it is called a positive ion. 6 protons (6+)6+ 6 electrons (6-)4- Neutral 0 (no charge)2+ (+ion)

Homework (if time) Page 273 – questions 1-5