- Notes:
- 1.) All matter is composed of tiny, indivisible particles called atoms, that cannot be destroyed or created
- 2.) Each element has atoms that are identical to each other in all of their properties, and these properties are different from the properties of all other atoms
- 3.) chemical reactions are simple rearrangements of atoms from one combination to another in small whole number ratios
- 4.) There are three parts to an atom. Protons have a positive electrical charge and are found together with neutrons (no electrical charge) in the nucleus of each atom. Negatively charged electrons orbit the nucleus.
- 5.) Atoms are mostly empty space. The nucleus of an atom is extremely dense and contains nearly all of the mass of each atom. Electrons contribute very little mass to the atom (it takes 1,836 electrons to equal the size of a proton) and orbit so far away from the nucleus that each atom is 99.9% empty space. If the atom was the size of a sports arena, the nucleus would be the size of a pea. Although the nucleus is much denser compared with the rest of the atom, it too consists mainly of empty space.
- 6.) There are over 100 different kinds of atoms. About 92 of them occur naturally, while the remainder are made in labs. The first new atom made by man was technetium, which has 43 protons. New atoms can be made by adding more protons to an atomic nucleus. However, these new atoms (elements) are unstable and decay into smaller atoms instantaneously. Usually, we only know a new atom was created by identifying the smaller atoms from this decay.
- 7.) The components of an atom are held together by three forces. Protons and neutrons are held together by the strong and weak nuclear forces. Electrical attraction holds electrons and protons. While electrical repulsion repels protons away from each other, the attracting nuclear force is much stronger than electrical repulsion. The strong force that binds together protons and neutrons is 1,038 times more powerful than gravity, but it acts over a very short range, so particles need to be very close to each other to feel its effect.
- 8.) The word “atom” comes from the Greek word for “uncuttable” or “undivided.” The name comes from the 5th century BCE Greek philosopher Democritus, who believed matter consisted of particles that could not be cut into smaller particles. For a long time, people believed atoms were the fundamental “uncuttable” unit of matter. While atoms are the building blocks of elements, that can be divided into still smaller particles. Also, nuclear fission and nuclear decay can break atoms into smaller atoms.
- 9.) Atoms are very small. The average atom is about one-tenth of a billionth of a meter across. The largest atom (cesium) is approximately nine times bigger than the smallest atom (helium).
- 10.) Although atoms are the smallest unit of an element, they consist of even tinier particles called quarks and leptons. An electron is a lepton. Protons and neutrons consist of three quarks each.
Another interesting fact about atoms is in 1834 Michael Faraday showed that electric current could cause chemical reactions to occur, demonstrating the electric nature of the elements.
