summary
● Matter is anything that occupies space.
● Matter can be an element or compound.
● An element is the basic building block of nature.
● A compound is a chemical combination of two or more elements.
● A molecule is the smallest unit of a compound that retains the properties of the compound.
● An atom is the smallest unit of matter that retains the structure of the element.
● An atom consists of a nucleus, which contains protons and neutrons. It also has one or more electrons that orbit around the nucleus.
● Protons have a positive charge, electrons have a negative charge, and neutrons have no charge.
● The atomic number of an element is the number of protons in the nucleus.
● The atomic weight of an atom is the sum of protons and neutrons.
● The orbits of the electrons are called shells.
● The outer shell of an atom is called the valence shell.
● The number of electrons in the valence shell is called the valence.
● An atom that has the same number of protons as electrons is electrically balanced.
● The process by which atoms gain or lose electrons is called ionization.
● The flow of electrons is called current.
● Current is represented by the symbol I.
● The charge of 6,240,000,000,000,000,000 (or 6.2431018) electrons is called a coulomb.
● An ampere of current is measured when 1 coulomb of charge moves past a given point in 1 second.
● Ampere is represented by the symbol A.
● Current is measured in amperes.
● An electric current flows through a conductor when there is an excess of electrons at one end and a deficiency at the other end.
● A source that supplies excess electrons represents a potential or electromotive force.
● The potential or electromotive force is referred to as voltage.
● Voltage is the force that moves electrons in a circuit.
● The symbol E is used to represent voltage.
● A volt (V) is the unit for measuring voltage.
● Resistance is the opposition to current flow.
● Resistance is represented by the symbol R.
● All materials offer some resistance to current flow.
● The resistance of a material is dependent on the material’s size, shape, and temperature.
● Conductors are materials with low resistance.
● Insulators are materials with high resistance.
● Resistance is measured in ohms.
● The Greek letter omega (Ω) is used to represent ohms.