All substances consist of matter. Matter is anything which has mass and takes up space. Some important concepts to remember about matter are:
- Matter is made up of one or more of over 92 naturally-occurring elements.
- Each element is a pure substance, made up of only one type of atom.
- An atom consists of three types of particles: protons, neutrons, and electrons. An atom does not need to have all three particles, but will always contain at least protons.
Electrons are negatively-charged particles, protons have a positive charge, and neutrons do not have an electrical charge.
- An atom has an inner core called a nucleus, which is where the protons and neutrons are located. The electrons orbit around the outside of the nucleus.
- Two main forces hold atoms together. The electric force holds the electrons in orbit around the nucleus. Opposite charges attract, so the electrons are drawn to the protons in the nucleus. The nuclear force holds the protons and neutrons together within the nucleus.
The Periodic Table
The periodic table is a chart which organizes the chemical elements. The elements are categorized according to the following attributes:
Atomic Number - number of protons in the nucleus
Atomic Mass - sum of the number of protons plus neutrons in the nucleus
Group - columns or multiple columns in the periodic table. Elements in a group share similar chemical and physical properties.
Period - rows from left to right in the period table. Elements in a period have the same number of energy shells.
Matter can exist in the form of a pure element, but combinations of elements are more common.
Molecule - a molecule is a combination of two or more atoms (could be from the same or different elements, such as H2 or H2O)
- Compound - a compound is a combination of two or more chemically-bonded elements. Generally, compounds are considered to be a subclass of molecules (some people will argue they are determined by the types of chemical bonds).
A chemical formula is a shorthand way of showing the elements contained in a molecule/compound and their ratio. For example, H2O, the chemical formula for water, shows that two atoms of hydrogen combine with one atom of oxygen to form a molecule of water.
Chemical bonds hold atoms together.
- Ionic Bond - formed when an electron transfers from one atom to another
- Covalent Bond - formed when two atoms share one or more electrons
Learn about the chemistry of life...