1. Unit E Chapter 1 “Atoms, Elements and Compounds” Lesson 1

2. Matter is Made of Atoms Democritus 460BCE – 370BCE Known as the “Father of Modern Science” He was also known as the “laughing philosopher” for his cheerfulness. Later writers thought it was his amusement with human follies.  If you were to cut something in half, how many times could you cut it?  Around 400BCE, the Greek philosopher Democritus said you would get a piece that could not be divided any further.  He named these tiny pieces “atoms.”  An atom is the smallest unit of a pure substance that still has the properties of that substance.

3. The Atomic Theory  While scientists and philosophers believed atoms were real, it wasn’t until the 1800’s that scientists could use experiments to study them.  An English chemist named John Dalton was the first to use experiments to support the “atomic theory.”  The atomic theory is the theory that matter is made of atoms.  Dalton thought atoms were the smallest pieces of matter and could not be divided further. He was proven wrong near the end of the century. John Dalton, not known as the “laughing chemist.”

4. The Atomic Theory  In 1897, J.J. Thomson showed that atoms are made of even smaller particles called “subatomic particles.”  He made a model of an atom to explain his findings, it was the first to show subatomic particles. Thomson’s atomic model

5. The Subatomic Particles  The nucleus is the center of an atom. It has a positive electrical charge and is made of at least one proton.  A proton is a subatomic particle with a positive charge.  A neutron is a subatomic particle with a neutral charge. It has roughly the same mass as a proton.

6. The Subatomic Particles  An electron is a negatively charged subatomic particle. They are much smaller than protons.  Protons and neutrons have nearly 2000 times the mass of an electron.  Electrons are in constant motion around the nucleus, acting like a cloud.  The flow of electrons from one atom to another is electricity. Electrons may be small but they can pack a wallop. This is a small example of the power of an atom.

7. The Nucleus  In 1911, Ernest Rutherford proved the existence of the nucleus.  He shot charged particles at gold foil, most traveled straight through but a few bounced back.  He inferred that atoms are mostly empty space. The diameter of the nucleus is 1/10,000 the diameter of the whole atom. Rutherford with his gold foil experiment

8. Isotopes and Ions  The atomic number is the number of protons in the nucleus.  Isotopes are atoms that have the same amount of protons but different amounts of neutrons.  Scientists measure the mass of an atom in atomic mass units or amu for short.  To find the atomic mass, add the number of protons and neutrons. These are all carbon atoms, but with different amounts of neutrons.

9. Isotopes and Ions  Ions are atoms that have gained or lost electrons, causing the atom to receive an electric charge.  Electrons are constantly being taken and lost between atoms. Ion cannons, found in Star Wars…..not in real life…..not yet anyway……..darn it.

10. Charges in Atoms  Because opposite charges attract, the positive charge of protons holds the negative electrons around the nucleus.  But if similar charges repel, why don’t the positive protons push apart from each other?  Overpowering this repulsion is a strong nuclear force.  This nuclear force holds the nucleus of an atom together. This is the first underwater nuclear test. This nuclear force holds the atoms together. When this force is released, the chain reaction is terrible.

11. Charges in Atoms  To find the charge of an atom, you must compare the amount of positive and negative charges (protons are positive, electrons are negative)  If an atom has 5 protons and 4 electrons, it has a charge of +1 because it has one more positive charge than negative charge.  If an atom has 5 protons but 7 electrons, it has a charge of -2 because it has 2 more negative than positive charges.  Positive and negative charges neutralize each other. If an atom has the same amount of protons and electrons, the atom has no charge, or is neutral.