Drawing Atoms. How many protons! How many neutrons? How many electrons? What element does thisatomrepresent?

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1 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 structures and helps us to understand similarities and differences among 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, because it shows important structures that houses are 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 representing houses. It is the same way with atoms. We can have drawings of atoms; we can have 3 dimensional models of atoms. We don't always need an extremely detailed model of an atom when we wish to compare similarities and differences among different types of atoms. The 3 most important structures or building blocks of atoms are the SUBATOMIC PARTICLES known as protons, neutrons and electrons. Protons have a positive charge and amass of 1 amu. Neutrons are not charges particles. Neutrons have a mass of 1 amu. Electrons have a negative charge and have a very small mass amu. PROTONS and NEUTRONS are located in the NUCLEUS, the center of the atom. ELECTRONS occupy energy levels outside the nucleus. The atomic number of an element is the same as the number of protons in an atom of the element. For instance, carbon has an atomic number of 6, which says that it has 6 protons in its nucleus. The number of neutrons in the nucleus of an atom can vary. When this happens, we say there are different ISOTOPES of an atom. Isotopes have the same number of protons, but different numbers of neutrons When we draw atoms, we will draw electrically neutral particles. We will always have the same number of protons as electrons. In this way, the positive and negative charges will cancel each other out, and the charge on the whole atom will be neutral. ' We can abbreviate the 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 many protons! How many neutrons? How many electrons? What element does thisatomrepresent?

2 2. Here are drawings of three What element do they represent? Do they all have the same mass? What is the name for this group of atoms? Do all atoms have neutrons? Do all atoms have protons? 3. When we draw atoms, we don't usually include the neutrons. Even though most atoms contain neutrons, they can vary because there are different isotopes. Here is a shorthand way to draw an What element do you think this is? How do you know? What do the numbers outside the inner circle represent? 4. Look at the following drawings of atoms. Name the elements

3 Electron Shells of Atoms When we draw atoms we need to show the shells that they occupy. Each shell has a maximum number of electrons that 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 semicircles that we use to show the positions of the electrons indicate the SHELL that the electrons are in. Electrons get farther and farther from the nucleus as you increase the shell number. Electrons don't fill the shells in order. There can be more ihun on. energy level in a shell, and it is possible for some electrons to be in the 4th shell, and then have the electrons go back to filling the 3'o shell, because there is an energy level in the 3'd shell that is higher than one in the 4th shell. Since this is a Physical Science course and not a Chemistry course, you are not responsible for learning the different energy levels. Instead, you will follow a Filling Order Table, so that you can place the proper number of electrons in each shell. Filli Order Table Shell # Maximum Number of Electrons I J J l T4 This table is not complete, but it is sufficient to draw the atoms we wish to draw. Rules o Note that once you fill the maximum number of electrons for a shell in the table, you must then go to the next shell in the filling ordet. o You may have less than the maximum number of electrons in a shell, but when you exceed the maximum you must go to the next row in the filling order table. o Note that the shells are not in order, but you must follow the order in the table for the correct drawing of the atom's electrons.

4 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 neutrons because these 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 electrons fill the 4th shell, there can be a maximum of 10 more electrons fillins the 3'd shell. Draw these atoms, using the same rules as shown for the atom above: Sulfur Chlorine Silver Xenon Strontium Barium Nickel Indium

5 Electrons and the Periodic Table What's the Pattern? The Periodic Table is an extremely useful tool for scientists. It literally shows the raw ingredients for any type of matter that has been constructed either by nature or by man. You will eventually learn rules for how atoms combine to form new compounds. You first need to understand the VALENCE ELECTRONS. Valence electrons are electrons in the outer shell of an atom. Use the Filling Order Table (from Electron Shells of Atoms) to draw the atoms of elements in 2 of the following columns of the Periodic Table: 1,2,13,14,15,16,17 and 18. (These columns comprise the group of families known as the representative elements.) o Draw all atoms in the 2 groups that you have chosen (or been assigned). Consult with other members of your group. Be prepared to present a statement to the class that summarizes any patterns that you observe as you examine your correct drawings of the atoms. Decide as a class- What is the maximum number of valence electrons that you observe after drawing the atoms?

6 Drawing Lewis Structures or Electron Dot Diagrams We can show the valence electrons (outer shell) of an atom using a Lewis Structure. A Lewis Structure or Electron Dot Diagram has some rules that you must follow. o The central part of the Lewis Structure is the element symbol. o The valence electrons are shown surrounding the element symbol. o Since there are never more than 8 valence electrons, we put them in a "box" shape around the element symbol. Two electrons on 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 electrons as possible, before we start pairing them. o The only exception to the above rule is helium. We know that the first shell holds 2 electrons only. We put helium's 2 electrons on the same side of the element symbol to indicate a full shell. The four sides of the element symbol are equivalent. It doesn't really matter what side you put the electrons on as long as you follow the other rules. Here are some Lewis Structures drawn for you. Helium Chlorine / l o ngo a 0 : tlo ' *t{$ox ;ct. ' t:-o '', r)rt*t1 o b il a rt ltnrys/ 6 c Calcium fl

7 Draw Lewis Structures for the following atoms: 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 Decide with the other members of your group on a rule or statement that explains how the Lewis Structure is related to an element's position on the periodic table. Be prepared to present your statement to the class.