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What is Matter Made Up Of? LESSON 1 Matter is Made Up of Atoms Democritus wondered how many times you could cut something in half and in half and in half until you could not cut it any smaller He called this the atom! This was about 2400 years ago! ATOM – Smallest unit of a pure substance that still has the properties of the substance It was not until the 1800’s when scientists were finally able to use experiments, not just ideas, to study these things Atoms are TINY! How many atoms do you think is in one grain of table salt? 2,000,000,000,000,000,000! That’s 2 quintillion or 2 billion billion atoms! John Dalton used experiments to support the Atomic Theory in the 1800’s, stating that matter is made up of atoms He also believed that atoms were the smallest particles of matter and cannot be divided Atomic Structure J.J. Thomson showed that atoms are made of even smaller particles called subatomic particles Plum Pudding Model Does anyone know an example of a subatomic particle? The atoms is made up many things!: Nucleus Proton Neutron Electron The Nucleus The center of an atom which contains protons and neutrons Ernest Rutherford’s famous experiment in 1911 showed that an atom had a nucleus Gold Sheet Experiment: https://www.youtube.com/watch?v=LMXNESnTc2c The nucleus is tiny compared to the size of the atom It is only about 1/10,000 the diameter of the atom So if the nucleus is a tennis ball, the atom would be the size of a about size football fields! Nucleus Despite it being a really small portion of the size, it makes up almost the entire mass! The nucleus is about 99.9% of the mass of the atom This is because a proton or neutron has about 2000X more mass than an electron! The number of protons contained in the nucleus determines what kind of atom it is Proton A proton is a subatomic particle that has a positive charge Usually found in the nucleus Every atom’s nucleus contains at least one proton! The number of protons in an atoms nucleus determines what type of atom it is Neutron Subatomic particle that has the same mass as a proton, but does not have electric charge Neutral charge Also found in the nucleus Electrons Negatively charged subatomic particle Electrons are in constant motion around the nucleus Mass is MUCH smaller than proton or neutron First thought that they were in “orbit” around nucleus Now we know they are in clouds around the nucleus that define the size of the atom Atomic Structure Atomic Number The number of protons in an atom is called the Atomic Number For example, the atomic number of Helium is 2, the atomic number of Carbon is 6? Give me some of your own examples: Isotopes All the atoms in an element have the same atomic number because they have the same number of protons! BUT… Atoms of the same substance may have different masses. Can anyone think of why this might be? It is actually because they have a different amount of neutrons! Atoms that have the same number of protons, but a different number of neutrons are called isotopes! Atomic Mass Units Atoms are really really small right?!? How do you think we measure the mass of a single atom? Grams? Pounds? Other guesses? We instead use atomic mass units or amu Every proton has the same mass and it is defined as 1 amu Neutrons have almost the same mass as a proton and so it also has a mass of 1 amu The atomic mass is the average of all the number of protons and neutrons in all of the isotopes of a substance AMU and Isotopes The atomic mass units of hydrogen isotopes are: 1 amu 2 amu 3 amu An isotope’s names is usually followed by the number of particles in the nucleus For example, a hydrogen with one proton and no neutrons would be Hydrogen-1 Charges What is the charge on a proton? What is the charge on an electron? I thought opposite charges attract… so why do the electrons stay on the outside of the nucleus and the protons are all next to each other? The strong nuclear force or atomic force keeps the nucleus together! An ion is an atom that has an electric charge on it! A neutral atom has no charge on it! Let’s do some examples! http://ed.ted.com/lessons/just-how-small-is-an- atom