The Periodic Table Questions
Bring on the tough stuff
1. What is ionization energy and what are its periodic trends? Explain.
2. What is electron affinity and what are its periodic trends?
3. What is an atomic radius and what are its periodic trends? Explain.
4. What is electronegativity and what are its periodic trends?
5. Chlorine and bromine are both found in the same group in the periodic table. Name the group. Are these elements metals or nonmetals? How many valence electrons do they have? Name a property that these two elements share.
6. Why are noble gases so inert?
7. Barium and magnesium are both found in the same group in the periodic table. What is the group called and what number is it? Also name two properties that they would be expected to share.
8. What is the general relationship between the size of an atom and its ionization energy?
9. Why are ionization energies always positive?
10. Why does F have a larger ionization energy that O?
Possible Answers
1. What is ionization energy and what are its periodic trends? Explain.
Ionization energy is the energy it takes to remove an electron from an atom. Ionization energy increases across a period because as the number of protons increases the atomic radius decreases. It is harder to take an electron off a small atom, so ionization energy increases. Ionization energy also decreases down a group for the same reason.
2. What is electron affinity and what are its periodic trends?
Electron affinity is the amount of energy absorbed when an electron is added to an atom. Electron affinity increases from left to right across the periodic table. This is caused by the decrease in atomic radius. Moving from left to right across a period, atoms become smaller and smaller as the atomic number increases. This causes the electron to move closer to the nucleus, thus increasing the electron affinity. Electron affinity decreases as we proceed down a group for the same reason.
3. What is an atomic radius and what are its periodic trends? Explain.
An atomic radius is total distance from an atom's nucleus to the outermost electron orbital. Atomic radii become smaller as you go from left to right across a period because the charge in the atom's nucleus becomes larger (increases Zeff). This increased charge pulls the electrons in closer. Atomic radii become larger as you go down a group because the outermost electrons are located in orbitals located further away from the nucleus (the principle quantum number, n, has increased).
4. What is electronegativity and what are its periodic trends?
Electronegativity is a measure of the attraction an atom has for electrons. As you move to the right across a period of elements, electronegativity increases. Atoms can either gain electrons or lose electrons. When the valence shell of an atom is less than half full (like on the left hand side of the periodic table), it's easier to lose an electron. When the valence shell of an atom is more than half full (like on the right side of the periodic table), it's easier to gain an electron. As you move down a group, electronegativity decreases. As we navigate down a group the atoms get bigger and bigger with more and more electrons. This means the outermost electrons get further and further away from the positively charged nucleus. Electronegativity decreases for this reason.
5. Chlorine and bromine are both found in the same group in the periodic table. Name the group. Are these elements metals or nonmetals? How many valence electrons do they have? Name a property that these two elements share.
Cl and Br are halogen elements. They are non-metals located in group seven. They are both chemically reactive, have low densities, and gases or liquids at room temperature, and they both are often found in their +1 oxidation state.
6. Why are noble gases so inert?
Noble gases are inert because they have the most stable electron configuration. Their valence shells are completely filled so they have no need or desire to lose or gain electrons.
7. Barium and magnesium are both found in the same group in the periodic table. What is the group called and what number is it? Also name two properties that they would be expected to share.
Ba and Mg are alkaline earth metals located in group two. The elements are chemically active, dense, good conductors, solids at room temperature, and silver in color.
8. What is the general relationship between the size of an atom and its ionization energy?
Larger atoms generally have lower ionization energies. This is because the outer electrons are further from the positively charged nucleus in a larger atom. This increased distance means a decreased attraction between the nucleus and the outer electrons. Less attraction equal lower ionization energy.
9. Why are ionization energies always positive?
Electrons are bound to an atom by electrostatic attractions to the nucleus. The negative electron is attracted to the positive nucleus. Therefore, energy must be added in order to remove an electron from an atom. Thus the ionization energy for this process is positive.
10. Why does F have a larger ionization energy that O?
Fluorine has a larger charge at its nucleus (Zeff¬) than O, but the valence electrons in both atoms are approximately the same distance away from the nucleus. Therefore, the electrons in F have a greater attraction to the nucleus and require more energy to be removed.