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The number of protons in the nucleus is what makes the element what it is. If there are 6 protons, then it is carbon. Your pencil “lead” is graphite, which is actually Carbon. If the atom has just one more proton, then it would be Nitrogen (78% of every breath you breath is Nitrogen). The difference between being a dark solid that you can write on your paper with, or a colorless, odorless gas that you breath is just one proton. But when it comes to reacting with other elements, it is the electrons that do all the work. Of course the electrons would not be with the atom if it weren’t for the positive charge of the protons keeping them there. www.zazzle.com For each proton that an element has in a neutral atom there is one electron. It is almost as if they were a matched pair that comes to a couples only dance party. Each electron must fit into an electron cloud around the nucleus, but there are only certain places that they can be. They always fill in a spot closest to the nucleus. Each shell can only hold so many electrons before it is full. This is similar to cars parking in a multi- level parking deck next to a restaurant. Everyone wants to park as close to the restaurant as possible. 8 Cars can fit 8 Cars can fit Parking Deck 8 Cars can fit 2 Cars can fit Restaurant The Bohr Model shows all of the electrons of an element in circular rings. Each ring represents an electron shell. It’s actually more complicated than this, but this is close 1st shell can hold 2 enough for 8th grade science 2nd shell can hold 8 3rd shell can hold 8 4th shell can hold 8 nicktoons.nick.com atomic number = # of protons for a neutral atom, # of protons = # of electrons atomic mass rounded to the nearest whole number is the mass number of the most common variety of the element Niels Bohr mass number - # of protons = # of neutrons So we need a 1+ in the middle to show Hydrogen’s 1 proton. We only have to put one electron. 1.008 rounds to 1, and 1-1=0 so there are no neutrons. 1+ 0n 6 protons (also means 6 electrons have to be there) 12.011 rounds to 12 (#p+ + #n0) subtract the 6 protons 12 – 6 = 6 (so it also has 6 neutrons) 6 protons 6 neutrons 6 electrons 6+ 6n Remember to follow the parking lot rules. Always start on the inner most ring and work outward. 18 protons (also means 6 electrons have to be there) 39.948 rounds to 40 (#p+ + #n0) subtract the 18 protons 40 – 18 = 22 (so it also has 22 neutrons) 18 protons 22 neutrons 18 electrons 18+ 22n Remember to follow the parking lot rules. Always start on the inner most ring and work outward. 19 protons (also means 6 electrons have to be there) 39.098 rounds to 39 (#p+ + #n0) subtract the 19 protons 39 – 19 = 20 (so it also has 20 neutrons) 19 protons 20 neutrons 19 electrons 19+ 20n Remember to follow the parking lot rules. Always start on the inner most ring and work outward. No matter how many layers the candy has, your tongue can only taste the outer most layer. The electrons of an atom are similar. Only the atoms on the outer most layer can interact with other elements. The outer most electrons are called the valence electrons. Since the Bohr model can get very difficult to read for larger elements, there is a way to show the element with just the valence electrons. It is the Lewis Dot Diagram. In the Lewis Dot Diagram we show the atomic symbol surrounded by dots that represent the valence electrons. Only these outer most electrons are represented. Generally speaking we start on the top and go around clockwise and only put dots on top, sides, and bottom. Gilbert N. Lewis www.123rf.com 1+ 0n 6+ 6n 18+ 22n 19+ 20n The Lewis Dot Diagram only shows the outer most electrons (valence electrons) surrounding the atomic symbol.