Drawing Atoms

Drawing Atoms When we draw atoms, we are making a model of an atom. It is not EXACTLY like a real atom, but it shows important structuresand helps us to understandsimilarities and differencesamong different types of atoms. When we draw a picture of a house,it is a model of a house. We recognizethe picture as a house,becauseit shows important structuresthat housesare made from (Doors, windows roofs, etc..) We can make very detailed drawings of houses;we can even make 3 dimensional models of houses. We would say that some are better models than others,but we can recognize all of them as representinghouses. It is the sameway with atoms. We can have drawings of atoms; we can have 3 dimensionalmodelsof atoms. We don't alwaysneedan extremelydetailedmodel of an atom when we wish to compare similarities and differencesamong different types of atoms. The 3 most important structuresor building blocks of atoms are the SUBATOMIC PARTICLES known as protons, neutronsand electrons. Protonshave a positive charge and amass of 1 amu. Neutrons are not chargesparticles. Neutrons have a maSSof 1 amu. Electrons have a negative chargeand have a very small maSS.0006amu. PROTONS and NEUTRONS are located in the NUCLEUS, the centerof the atom. ELECTRONS occupy energy levels outsidethe nucleus. The atomic number of an elementis the sameas the number of protons in an atom of the element. For instance,carbon has an atomic number of 6, which saysthat it has 6 protons in its nucleus. The number of neutronsin the nucleus of an atom can vary. When this happens,we say there are different ISOTOPES of an atom. Isotopeshave the samenumber of protons, but different numbersof neutrons When we draw atoms, we will draw electrically neutral particles. We will always have the samenumber of protons as electrons. In this way, the positive and negative chargeswill cancel each other out, and the chargeon the whole atom will be neutral. ' We can abbreviatethe word proton using this symbol - p+ Neutron can be abbreviated- n Electron can be abbreviated- e- 1. Here is a drawing of an atom. How manyprotons! How manyneutrons? How manyelectrons? Whatelementdoesthis atom represent? 2. Here are drawings of three atoms. @ Whatelementdo they represent? Do they all havethe samemass? Whatis the namefor this groupof atoms? Do all atomshaveneutrons? Do all atomshaveprotons? 3. Whenwe draw atoms,we don't usuallyincludethe neutrons.Eventhough mostatomscontainneutrons,they canvary becausetherearedifferent isotopes.Hereis a shorthandway to drawan atom. @Dj Whatelementdo you think this is? How do you know? Whatdo the numbersoutsidethe innercirclerepresent? 4. Look at the following drawingsof atoms.Namethe elementsthey represent. @))) @)?) Electron Shellsof Atoms When we draw atoms we needto show the shells that they occupy. Each shell has a maximum number of electronsthat it can hold. When we draw atoms, we have a "filling order" for the electrons. Electrons occupy the lowest energy level until it is full, then they go to the next higher and the next higher. The semicirclesthat we use to show the positions of the electronsindicate the SHELL that the electronsare in. Electrons get farther and farther from the nucleus as you increasethe shell number. Electrons don't fill the shells in order. There can be more ihun on. energylevel in a shell, and it is possiblefor someelectronsto be in the 4thshell, and then have the electrons go back to filling the 3'o shell, becausethere is an energy level in the 3'd shell that is higher than one in the 4thshell. Sincethis is a Physical Sciencecourseand not a Chemistry course,you are not responsiblefor learning the different energy levels. Instead,you will follow a Filling Order Table, so that you can place the proper number of electronsin each shell. Filli Order Table Shell # Maximum Number of Electrons I J 2 8 8 4 2 2 J 4 5 4 5 6 4 10 6 2 l0 6 2 T4 This tableis not complete,but it is sufficientto drawthe atomswe wish to draw. Rules o Note that onceyou fill the maximumnumberof electronsfor a shellin thetable, you mustthengo to the next shellin the filling ordet. o You may havelessthanthe maximumnumberof electronsin a shell,but when you exceedthe maximumyou mustgo to the next row in the filling ordertable. o Note that the shellsarenot in order,but you mustfollow the orderin thetablefor thecorrectdrawingof the atom'selectrons. This is a drawing of an atom of Titanium, atomic number 22. lt shows 22 protons in the nucleus and22 electrons. We don't show the neutronsbecausethese can vary due to different isotopes. Notice that there are 2 numbers shown on the 3'd shell. This is due to the filling order shown in the table. After 2 electronsfill the 4thshell, there can be a maximum of 10 more electronsfillins the 3'd shell. Draw theseatoms, using the samerules as shown for the atom above: Sulfur Chlorine Silver Xenon Strontium Barium Nickel Indium Electrons and the Periodic Table What's the Pattern? The Periodic Table is an extremely useful tool for scientists. It literally showsthe raw ingredientsfor any type of matter that has been constructedeither by nature or by man. You will eventually learn rules for how atoms combine to form new compounds. You first needto understandthe VALENCE ELECTRONS. Valence electronsare electronsin the outer shell of an atom. Use the Filling Order Table (from Electron Shells of Atoms) to draw the atoms of elementsin 2 of the following columnsof the PeriodicTable: 1,2,13,14,15,16,17 and 18. (Thesecolumns comprisethe group of families known as the representativeelements.) o Draw all atoms in the 2 groupsthat you have chosen(or been assigned). Consult with other membersof your group. Be preparedto presenta statementto the classthat summarizesany patternsthat you observeas you examine your correct drawings of the atoms. Decide as a class- What is the maximum number of valence electronsthat you observeafter drawing the atoms? Drawing Lewis Structuresor Electron Dot Diagrams We can show the valence electrons(outer shell) of an atom using a Lewis Structure. A Lewis Structureor Electron Dot Diagram has somerules that you must follow. o The central part of the Lewis Structureis the element symbol. o The valence electronsare shown surroundingthe element symbol. o Since there are never more than 8 valence electrons,we put them in a "box" shape aroundthe element symbol. Two electronson each side of the box. o Electrons are all negative. To show that they repel each other and would rather stay away from each other if they could, we have as many unpaired electronsas possible,before we start pairing them. o The only exception to the aboverule is helium. We know that the first shell holds 2 electronsonly. We put helium's 2 electronson the sameside of the element symbol to indicate a full shell. The four sidesof the element symbol are equivalent. It doesn't really matter what side you put the electronson as long as you follow the other rules. Here are some Lewis Structuresdrawn for you. Helium / l ila o ngo ' rt ltnrys/ *t{$ox r)rt*t1 ob a 0 Chlorine :t L o 6 c Calcium fl ' ;ct. t:-o '', Draw Lewis Structuresfor the followingatoms: 1) H Li Na K 2) Be Mg Ca Sr 13) B AI Ga In r4) C Si Ge Sn 1s) N P As Sb 16) o S Se Te 17) F CI Br I 18) Ne Ar Kr Xe that explainshow the Decidewith the othermembersof your groupon a rule or statement Lewis Structureis relatedto an element'spositionon the periodictable. Be preparedto presentyour statementto the class.