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Matter & The Atom Matter The term matter describes all of the physical substances around us Matter is anything that has mass and takes up space The Universe is made up of matter and energy *Matter is made up of atoms. *An atom is the smallest whole particle of matter. * Sub-Atomic particles are smaller than atoms and are the tiny particles that an atom is made of. Atomic Structure Nucleus – Protons – Neutrons Electrons Atomic Structure Electrons Tiny, very light particles Have a negative electrical charge (-) Move around the outside of the nucleus Atomic Structure Protons Much larger and heavier than electrons Protons have a positive charge (+) Located in the nucleus of the atom Atomic Structure Neutrons Large and heavy like protons Neutrons have no electrical charge Located in the nucleus of the atom Atomic Structure How small is an atom? Since the atom is too small to be seen even with the most powerful microscopes, scientists rely upon models to help us to understand the atom. http://www.youtube.com/watch?v=yQ P4UJhNn0I Who discovered atoms? Democritus (460- 360 BC) He came up with the idea that matter was made up of small units. He actually created the term “atom” J.J. Thompson In 1897, Thompson thought that the atom must be made of negative charges that were stuck in a positively charged material. This was called the plum pudding model. Rutherford Shot particles at a thin sheet of gold foil. He expected the particles to pass though. Most did, BUT some were deflected and bounced back Realized that the mass of an atom was not spread out evenly, but rather it was concentrated and positively charged Usually given credit for discovering the proton Early Models of the Atom Rutherford Mostly empty space Small, positive nucleus Contained protons Negative electrons scattered around the outside Early Models of the Atom Bohr Electrons move in definite orbits around the nucleus Meaning they follow a pattern Modern Model of the Atom The electron cloud Sometimes called the wave model Spherical cloud of varying density Varying density shows where an electron is more or less likely to be Describing Atoms Atomic Number = number of protons In a neutral atom, the # of protons = the # of electrons Atomic Mass= the number of protons + the number of neutrons Ions An atom that carries an electrical charge is called an ion If the atom loses electrons, the atom becomes positively charged (because the number of positively charged protons will be more the number of electrons) If the atom gains electrons, the atom becomes negatively charged (because there are more negative charges than positive) Ions The number of protons does not change in an ion. The number of neutrons does not change in an ion. So, both the atomic number and the atomic mass remain the same. Ions This atom has lost an electron. Now it has one more proton than electron. One more proton means one more positive charge. This makes the total charge of the atom POSITIVE. This atom has gained an electron. Now it has one less proton than electron. One less proton means one less positive charge. This makes the total charge of the atom NEGATIVE. Isotopes The number of protons for a given atom never changes. The number of neutrons can change. Two atoms with different numbers of neutrons are called isotopes Isotopes have the same atomic # Isotopes have different atomic Mass #’s Isotopes Electrons have special rules…. You can’t just shove all of the electrons into the first orbit of an electron. Electrons live in something called shells or energy levels. Only so many can be in any certain shell. Created by G.Baker www.thesciencequeen.net Nucleus 1st shell 2nd shell 3rd shell So let’s try it…. How to draw a Lithium atom First, look at the Periodic Table Second, determine the number of protons (Look @ the atomic number) Then determine the number of neutrons (Atomic mass – atomic number) Then determine the number of electrons (Look @ the atomic number) 3 Li Lithium 7 So let’s try it…. Protons = 3 3 + + + - Li - Lithium 7 Electrons = 3 Neutrons = 4 2 in the 1st shell, 1 in the 2nd shell (7-3=4) Lewis Dot Structure The Lewis Dot Structure is a bit different from the Bohr model. It only shows the element symbol and it’s outer most electron shell. - - - + + + + - - + + + + - - • • O •• •• - How to… 1. Write the symbol. 2. Start on the right hand side, working your way clockwise around the symbol. 3. Try Lithium Created by G.Baker www.thesciencequeen.net Your activity… Using the beans (Lentils are electrons, Lima Beans are protons, and kidney beans are neutrons), create a Bohr model , and then a Lewis dot structure model of each of the first 20 elements. After you have created each model, draw each model on your chart. Hint to make a chart, use a burrito fold, then fold the top down by 1 ½ inches. Unfold, you now have 3 columns. Label Created by G.Baker www.thesciencequeen.net