Chemistry Unit 3 – Periodic Trends

Name……………………………………...…….. Hour…….

The periodic table is often considered to be the “best friend” of chemists and chemistry students alike. It includes information about atomic masses and element symbols, but it can also be used to make predictions about atomic size, electronegativity, ionization energy, bonding, solubility and reactivity. In this activity you will look at a few periodic trends that can help you make those predictions. 1. Consider the data in Model 1 on the following page. a. Write a complete sentence to convey your understanding of atomic radius. Note: You may not use the word “radius” in your definition. ___Distance from the nucleus to the outermost valence electron___ b. In general, what is the trend in atomic radius as atomic number increases in a vertical column on the periodic table? Note: Columns on the periodic table are often called “families” or “groups”. ___The radius increases as atomic number increases in a family___ c. Using your knowledge of Coulombic attraction and the structure of the atom, explain the trend in atomic radius that you identified above. Hint: You should discuss either a change in distance between the nucleus and valence electrons or a change in the number of protons in the nucleus. ___In a family more energy levels are added and thus the distance from the nucleus to a valence electron (radius) increases)___ d. In general, what is the trend in atomic radius as atomic number increases in a period on the periodic table? Note: Rows on the periodic table are called “periods”. ___The radius decreases as atomic number increases in a period___ e. Using your knowledge of Coulombic attraction and the structure of the atom, explain the trend in atomic radius that you identified above. Hint: You should discuss either a change in distance between the nucleus and valence electrons or a change in the number of protons in the nucleus. ___In a period no new energy levels are added, more protons are added to the nucleus and thus the Coulombic attraction between the nucleus and a valence electron increases, resulting in a decreased radius. Page 1 of 5

Model 1 – Main Group Elements

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2. Locate the numbers in Model 1 that represents the ionization energy. The ionization energy is the amount of energy needed to remove a valence electron from an atom in its gaseous state. Mg(g) → Mg1+(g) + 1eIE = 738 kJ/mol a. Using your knowledge of Coulombic attraction, explain why ionization – removing an electron from an atom – takes energy. ____Negatively charged electrons are attraction to the positive protons in the nucleus. Consequently, energy is required to break this attraction and remove an electron. b. Which takes more energy, removing an electron from an atom where the nucleus has a tight hold on its electrons, or a weak hold on its electrons? Explain. ___More energy would be required if the attraction was strong.___ c. In general, what is the trend in ionization energy as atomic number increases in a family/group on the periodic table? ___Ionization energy decreases; it is easier to remove an electron___ d. Using your knowledge of Coulombic attraction and the structure of the atom, explain the trend in ionization energy that you identified above. Hint: You should discuss either a change in distance between the nucleus and valence electrons or a change in the number of protons in the nucleus. ___In a family the valence electron is farther from the nucleus and experiences a smaller Coulombic attraction from the protons in the nucleus. Consequently the valence electron is less attracted to the nucleus and less energy is required to remove it.___ e. In general, what is the trend in ionization energy as atomic number increases in a period on the periodic table? ___In general the ionization energy increases; more energy is required to remove a valence electron. ___

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f. Using your knowledge of Coulombic attraction and the structure of the atom, explain the trend in ionization energy that you identified above. Hint: You should discuss either a change in distance between the nucleus and valence electrons or a change in the number of protons in the nucleus. ___In a period the radius decreases and the number of protons in the nucleus increases. As a consequence, a valence electron experiences a larger Coulombic attraction from the nucleus and more energy is required to remove a valence electron.___ 3. Atoms with loosely held electrons are usually classified as metals. They will exhibit high conductivity, ductility (ability to be pulled into a thin wire) and malleability (bendable) because of their atomic structure. a. Would you expect metals to have high ionization energies or low ionization energies? ___Metals should have low ionization energies – electrons are easily removed___ b. Would you expect metals to be more on the left side or right side of the periodic table? ___Left side of the periodic table as IE increases in a period___ Electronegativity is a measure of the atom’s nucleus to attract electrons from a different atom within a covalent bond (a bond between non-metal atoms). A higher electronegativity value correlates to a stronger pull on the electrons in a bond. 4. Circle the letter of the best visual representation of electronegativity. Letter B

5. Locate the electronegativity values in Model 1. a. What is the trend in electronegativity as atomic number increases in a family/group? ___Electronegativity decreases as atomic number increases in a family.___

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b. Explain the existence of the trend described above in terms of atomic structure and Coulombic attraction. ___In a family the radius increases as shielding increases and effective nuclear charge remains constant. Consequently, it is difficult for the nucleus in one atom to attract electrons in another atom resulting in a smaller electronegativity.___ c. What is the trend in electronegativity as atomic number increases in a period? ___Electronegativity increases (easier to attract an electron from a neighboring atom).___ d. Explain the existence of the trend described above in terms of atomic structure and Coulombic attraction. ___As atomic number increases in a period the radius decreases, shielding remains constant and effective nuclear charge increases. Consequently, it is easier for the nucleus in one atom to attract electrons in another atom resulting in a larger electronegativity.___

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