Chemistry 1 Worksheet 9 Atomic Number, Mass Number, and Isotopes of Elements 1
You will need a periodic table to complete this worksheet. 1. Label the subatomic particles below with the appropriate charge. (+, -, or neutral). a. Proton b. Electron c. Neutron 2. How many protons and electrons are in the atoms below? a. Iron (Fe) b. Gold (Au) c. Copper (Cu) d. Francium (Fr) 3. An atom was determined to have 44 protons. Which element is this? 2
4. A generalized structure of a beryllium (Be) atom is shown below. Label all the subatomic particles and include correct charges. 3
5. The periodic table entry for chlorine is shown to the right. a. What is the chemical symbol of this element? b. How many protons are in this element? c. What is the atomic mass of this element? 6. An atom of titanium (Ti) has 22 protons, 22 electrons, and 26 neutrons. a. What is the atomic number (Z) of Titanium? b. What is the mass number of titanium? 4
c. Use this information to fill out the periodic table entry for titanium below. 7. Review: The mass of a proton is 1.672622 x 10-27 kg. What is the mass of two protons in mg. 5
8. Two isotopes of helium (He) are represented by the diagrams below. a. What is the mass number of each of the two isotopes? b. What would these isotopes be called? Mass number: 6
9. Explain why the atom depicted on the right below is not an isotope of hydrogen. 10. Two of the known isotopes of fluorine are 18 F and 19 F. How many neutrons does each of the two isotopes contain? 11. Complete the data table for the following isotopes. a. 106 Ru # neutrons: # protons: b. 75 As # neutrons: # protons: c. 79 Br # neutrons: # protons: d. 40 Ar # neutrons: # protons: 7
12. Use the way of A E to write the following isotopes: Z a. Germanium-74 b. Indium-115 c. Americium-241 d. Nitrogen-15 8
Answer Key 1. Label the subatomic particles below with the appropriate charge. (+, -, or neutral). Correct answer: a. Proton + b. Electron - c. Neutron Neutral (no charge) 2. How many protons and electrons are in the atoms below? a. Iron (Fe) To answer this, just look at the periodic table entry for iron. Remember, the atomic number (Z) represents the number of protons that each element has. Also remember that the number of protons equals the number of electrons in a neutral molecule. Correct answer: 26 protons and 26 electrons. b. Gold (Au) 9
The atomic number of gold is 79. Correct answer: 79 protons and 79 electrons. c. Copper (Cu) Correct answer: 29 protons and 29 electrons. d. Francium (Fr) Correct answer: 87 protons and 87 electrons 3. An atom was determined to have 44 protons. Which element is this? To find this, we need to remember that the number of protons determines the atomic number of that element. So, an element with 44 protons would be element #44 on the periodic table. Correct answer: Ruthenium (Ru) 10
4. A generalized structure of a beryllium (Be) atom is shown below. Label all the subatomic particles and include correct charges. How will we figure this out? The easiest way is to work our way from the outside in. The only two subatomic particles that exist in the nucleus are the proton and neutron. That means that the 4 circles outside of the nucleus must be the remaining subatomic particle, the electron (e - ). Now, remember that for a neutral species, the number of electrons always equals the number of protons. Since there are 4 blue circles, those must be the protons (p + ). By process of elimination, the remaining grey spheres are neutrons (n). Correct answer: 11
5. The periodic table entry for chlorine is shown to the right. a. What is the chemical symbol of this element? The chemical symbol is just the letters in the center of the entry. In this case, Cl. Correct answer: Cl b. How many protons are in this element? The number of protons is equal to the atomic number, 17. Correct answer: 17 c. What is the atomic mass of this element? The atomic mass is always listed at the bottom, so 35.45 amu. Correct answer: 35.45 amu 6. An atom of titanium (Ti) has 22 protons, 22 electrons, and 26 neutrons. a. What is the atomic number (Z) of Titanium? Correct answer: 22 (Z = the number of protons) b. What is the mass number of titanium? Correct answer: 48 (mass number = protons + neutrons) 12
c. Use this information to fill out the periodic table entry for titanium below. 7. Review: The mass of a proton is 1.672622 x 10-27 kg. What is the mass of two protons in mg. 1.672622 x 10-27 kg 1,000 g 1,000 mg = 1.672622 x 10-21 mg 1 kg 1 g Just multiply this answer by 2. Correct answer: 3.345244 x 10-21 mg 13
8. Two isotopes of helium (He) are represented by the diagrams below. a. What is the mass number of each of the two isotopes? b. What would these isotopes be called? Mass number: 4 3 Isotope: 4 He (or Helium-4) 3 He (Helium-3) 14
9. Explain why the atom depicted on the right below is not an isotope of hydrogen. Remember, an isotope is a variant of an element that differs only by the number of neutrons. The atom depicted on the right varies by its number of protons. Also remember that an atom s identity is determined by the number of protons it contains. Thus, the atom on the right is a completely different element (He). Correct answer: the atom on the right has an extra proton and is a different element. 15
10. Two of the known isotopes of fluorine are 18 F and 19 F. How many neutrons does each of the two isotopes contain? The mass number in the superscript represents the combined number of neutrons and protons. The atomic number of fluorine (F) is 9, which represents the number of protons, which is a constant. To get the number of neutrons, we just need to subtract 9 from both 18 and 19. Correct answer: 18 F has 9 neutrons; 19 F has 10 neutrons. 11. Complete the data table for the following isotopes. a. 106 Ru # neutrons: 62 # protons: 44 b. 75 As # neutrons: 42 # protons: 33 c. 79 Br # neutrons: 44 # protons: 35 d. 40 Ar # neutrons: 22 # protons: 18 12. Use the way of A E to write the following isotopes: Z a. Germanium-74 b. Indium-115 74 115 49In 32Ge c. Americium-241 d. Nitrogen-15 241 95Am 15 7N 16