Science Exam: Chemistry & Electricity

Section A: Easy

5 points of the particle theory

  1. All matter is made up of particles

  2. The spaces between the particles are large compared to the particles themselves

  3. All particles of one substance are the same, different substances are composed of different types of particles

  4. The particles are in constant motion(random)

Physical Properties

A characteristic that you can measure and observe without needing a chemical property. Some examples are:

  • State

  • Colour

  • Lustre

  • Hardness

  • Brittleness

  • Malleability

  • Ductility

Chemical Change

Results in the formation of a new substance and the substance you started with is not going to be the same as the substance you started with. Chemical changes change the identity of a pure substance.

5 signs:

  1. Heat has been absorbed or given off

  2. Light has been given off

  3. A precipitate forms

  4. A gas forms or has an odor

  5. A new colour appears

Counting Atoms in a Compound

Originally, there are two or more atoms in a compound depending on the element. E.g. Water(H2O) has 2 and Methane(CH4) has 4.

Another way is that if we’re given an equation like: (NH4)2SO4

The 2 after the parenthesis is multiplying the elements in the bracket. Nitrogen has no subscript, which means it has a 1. 1 × 2 = 2 so Nitrogen has 2 atoms. Hydrogen has 4 as its subscript, 4 × 2 = 8 atoms. For sulfur and oxygen it will be the same but without multiplying by 2.

Subatomic Particles

An atom is made up of protons, neutrons and electrons.

Protons: Symbol - P, mass - 1u, charge - 1+, location - nucleus

Neutrons: Symbol - N, mass - 1u, charge - 0, location - nucleus

Electrons: Symbol - E, mass - 0.0005u, charge - 1-, location - energy level/orbits/shells

u = an extremely small unit of mass, used to measure the mass of atoms.

Atomic Number: The number of protons in the nucleus of that atom. Every element has a unique atomic number, which is equal to the number of electrons in a neutral (uncharged) atom.

To find neutrons, we subtract the rounded atomic mass with the atomic number.

For example: Find the neutron of Phosphorus(P). So we’ll subtract 31(mass) with 15(atomic number) which is 16 neutrons. And the electrons are written the same as the protons.

Law of Electric Charges

There are three laws of electric charges:

  1. Unlike charges attract

  2. Like charges repel

  3. A charged object attracts an electrically neutral object.

Charging by Friction

Electrons can be transferred when two different neutral substances are rubbed against each other. This only works if both the substances are insulators as the charge must build.

When two neutrally charged objects are rubbed together, one becomes positively charged (loses electrons) and the other becomes negatively charged (gains electrons).

The direction of electric flow is determined by and electrostatic series.

The higher an object is on the electrostatic series, the weaker its' hold is on electrons, and the lower the object is the stronger.

Insulators and Conductors

Insulators: An electrical insulator is a material in which charges cannot move easily. E.g. rubber, glass, oil, diamond, dry wood, etc.

Conductors: An electrical conductor is a material in which electrons move easily. They do not conduct very well because their electrons move freely. E.g. silver, gold, copper, steel, sea water, etc.

In insulators, the negative charges cannot move, so if there’s a fur cloth near it, then the electrons will only shift towards it a little but not move. It’s the complete opposite for a conductor because the electrons move freely, so the almost all the negative charges will freely move to the side where the fur is being held.

Definition of V, I, R

Voltage: also known as potential difference is the difference in electrical potential energy in two places in a circuit.

Current: The flow of electricity in a circuit, the amount of electricity flowing through a circuit.

Resistance: Opposes the push from a voltage source and effects the speed of the current.

Ohm’s Law

States the relationship between voltage, current and resistance.

Current = Voltage/Resistance

Resistance = Voltage/Current

Voltage = Current x Resistance