35Cl or mass number Symbol This is because if you write the element symbol, such as Cl, you know the atomic number is 17 from that symbol. Remember that the atomic number, or number of protons in the nucleus, is what defines the element. Thus, if 17 protons are in the nucleus, the element can only be chlorine. Sometimes you will only see 35C1, where the atomic number is not written. Watch this video to review the format for written symbols. In the following table each column represents a neutral atom. Fill in the gaps in the following table by working this problem out on a separate sheet of paper. You will need the periodic table in the "resources" drop down menu in the upper right hand corner of this question to look up atomic numbers. Symbol 1 Protons 26 82 Neutrons 30 66 Electrons 49 86 Mass no. 222 207 Use the hints in the following part whenever needed to review the steps to filling in this type of table. 17 Part A Once you have filled in all the gaps on a separate sheet of paper, enter the four missing element symbols in the first row of the table into the answer box below. You can open the first hint to view a video that steps you through filling in the first column of the table. Enter the four missing symbols for the first row of the table from left to right, separated by commas, into the answer box below. Use the stacked super/subscripts button (available in the templates button menu above the answer entry box) to enter the symbols in the following form: muss number Symbol, or for example, ci Express your answers as chemical symbols. atomic