EXERCISE 5-2 Periodic Properties of the Elements


1	The questions in this exercise require the use of graphs of different periodic properties of the elements as a function of atomic number. These graphs are available in most preparative and general chemistry texts and can also be obtained directly by going to the WebElements site: http://www.webelements.com/ At this site you will have to learn to navigate around to reach the graphs. How does the covalent radius vary as the atomic number increases going across a period?
		The radius increases as the number of electrons increase.
		The radius decreases due to the increased attraction by the increasing number of protons.
		The radius is relatively the same going across a period.
		None of the previous answers.


2	How does the covalent radius vary as the atomic number increases going down a group or family?
		The radius increases as some of the electrons must go into a higher quantum level..
		The radius decreases due to the increased attraction by the increasing number of protons.
		The radius is relatively the same going down a period.
		None of the previous answers.


3	*How does the first ionization energy (called ionization enthalpy at WebElements) vary as the atomic number increases going across a period?*
		The ionization energy generally decreases as the electrons are farther from the nucleus.
		The ionization energy generally increases due to the increased attraction by the increasing number of protons.
		The ionization energy is relatively the same going across a period.
		None of the previous answers.


4	Close inspection reveals two apparent discrepancies in the general trend for the first ioniztion energy going across periods 2 and 3. Why does the ionization energy drop going from group IIA to IIIA?
		The error range of the measurements is greater than the discrepancy.
		There is more electron repuslsion.
		The last electron that goes into the IIIA goes into a p orbital. This sublevel is a little higher in energy (and therefore closer to the ionization level) than the s orbital.
		None of the previous answers.


5	Why does the ionization energy drop going from group VA to VIA?
		The error range of the measurements is greater than the discrepancy.
		There is more electron repuslsion as the last electron has to pair up with another electron.
		None of the previous answers.



6	*How does the first ionization energy (called ionization enthalpy at WebElements) vary as the atomic number increases going down a group or family?*
		The ionization energy increases as some of the electrons must go into a higher quantum level..
		The ionization energy decreases as the outer electrons are going into higher quantum level (and farther away from the nucleus) orbitals.
		The ionization energy decreases due to the increased attraction by the increasing number of protons.
		None of the previous answers.


7	Is there any correlation between thermal conductivity and position in the periodic table?
		Non-metals have higher thermal conductivities than metals.
		There is no correlation.
		Metals have higher thermal conductivities than non-metals and there are some groups of metals that are better than others but the correlation is rough.
		The alkali metals are the best conductors.
		None of the previous answers.

8	In addition to periodic properties, the WebElements site [http://www.webelements.com/] contains a plethora of information about elements. There is strong evidence that a meteor impact with the earth 65 million years ago caused the extinction of many types of life forms. Whether this event was responsible for the extinction of the dinosaurs is still being debated. Part of the supportive evidence for this meteor impact theory was discovered by the late Dr. Walter Alvarez who found abnormally high concentrations of iridium in a narrow layer of earth at several locations around the earth. At the WebElements site, click on iridium Geology under the "iridium around us" heading. What is the concentration of iridium in the earth's crustal rocks and in carbonaceous meteors (in ppb by weight) respectively?
		2 ppb, 2 ppb
		0.4 ppb, 550 ppb
		0.01 ppb, 0.01 ppb
		None of the previous answers.