Element Analysis (Databases, Graphing)

From the Sourcebook for Teaching Science (chapter 19)

• Use the  Element Database to answer the questions in these activites

Forensic science is the application of science to law. Forensic scientists are used as expert witnesses in court cases to establish facts.  A physicist might testify concerning ballistics in a murder trial. A chemist might testify regarding the composition of air or water in an environmental lawsuit.  A biologist might testify concerning DNA samples in a biotechnology product dispute.  Forensic scientists often make their conclusions by comparing current observations with ones compiled in a database.  For example, a forensic chemist might identify a pollutant by comparing its NMR-spectrum (nuclear magnetic resonance spectrum) with the NMR-spectra of other chemicals cataloged in an NMR database.  In this chapter we use databases to categorize, sort, compare, and analyze information to answer questions and solve problems.

Graphing Trends in the Periodic Table

PTable allows you to make heat maps of the properties of the elements.

Periodic Table allows you to graph the properties of the elements as a function of atomic number.

Use the  Element Database to graph:

• Atomic Radius as a function of Atomic Number

• First Ionization Energy as a function of Atomic Number

• Electron Affinity as a function of Atomic Number

• Melting Point as a function of Atomic Number

• Freezing Point as a function of Atomic Number

• A property of your choice as a function of Atomic Number

Describe and explain the patterns you see in these graphs

Choosing the right material

By 1700, only 14 elements (carbon, sulfur, iron, copper, zinc, arsenic, silver, tin, antimony, gold, mercury, lead, bismuth, and phosphorous) and a few compounds were known. The industrial revolution, which began in the 18th century, established a demand for new resources, and gave incentive for chemists to purify, develop, and classify new materials.  The phenomenal expansion in commercial products that occurred in the industrial age is a direct result of the development of the chemical and materials sciences.  Materials science focuses on the properties of materials that make them suitable for industrial applications.  Chemists have now have identified more than 110 elements, more than 23,000,000 compounds, and are identifying more than 4000 new compounds per day.  It is impossible for developers to remember the properties of so many substances, yet they must select the best compounds to produce the best products for today’s competitive market.  Developers rely upon electronic databases to search for materials with desired characteristics.  In this activity, you will use a database file of the elements (table 19.2) to search for those with the specified properties.  Download the elements file (sciencesourcebook.com) or enter the data from table 19.2 into a new file. 

(1) Electronic circuits:  When designing electronic circuits, computer hardware engineers must use materials that have extremely high conductivity so signals travel easily with little loss of energy.  Sort (arrange) the database list on electrical conductivity to determine the three best elements for use in electric circuitry.  Where are these three elements found in the periodic table?  Perform an Internet search to determine if these elements are indeed used in electrical circuits.

(2) Aircraft design:  Aircraft designers need materials that can withstand extreme temperatures and are lightweight, malleable, and abundant.  Determine the element that best fits these criteria. Using a filter, select those substances that are metallic (all metals are malleable), have a melting point in excess of 600K, and a density less than 3 g/cm3.  Finally, sort these elements by abundance in the earth's crust to determine which is the most abundant.  Which element fills these criteria?  Perform an Internet search to determine the element of which most airplanes are made.  Is this the same element you selected using your database filter?

(3) Electric switches:  Certain applications require fluid conductors -- materials that conduct electricity and yet flow at room temperature.  Perform a record selection (filter) for those elements with a melting point less than 298K, and a boiling point greater than 298K.  This selects for those elements that are liquid at room temperature, 298K (25°C).  Following this record selection (filter), sort descending on electrical conductivity.  The element at the top of the list will be the best liquid conductor at room temperature. What is this element?

Arranging elements by physical properties

(1) Abundance:  Coins and jewelry are normally made of rare elements so that they have intrinsic value and are difficult to counterfeit. By contrast, metals used in construction are abundant and inexpensive, keeping construction costs down. Sort (arrange) the elements database (table 19.2, available online at www.sciencesourcebook.com) by abundance in the Earth’s crust and determine if these generalizations hold true.  Research the relative abundance of gold, iron, copper, aluminum, silver, and platinum and determine which are better suited for coins or construction on the basis of this single criteria.

(2) Element symbols:  Most element symbols are derived from the first one or two letters of the element name.  For example, the symbol for oxygen is O and the symbol for helium is He.  This is not true for all elements, however.  For example, the symbol for potassium is K, even though there is no such letter in the name.  Determine if there is a correlation between the date of discovery and the symbol/name convention.  Sort (arrange) the elements by date of discovery, and compare the element names with the symbol names.  Is there greater correlation between the names of elements and their symbols for recently discovered elements, or for ones discovered many years ago?  Explain.

(3) Ionization potential:  Ionization potential (energy) is the energy required to remove an electron from a neutral atom.  Elements with a low ionization energy easily loose electrons and become cations, while those with high ionization energy hold on to their valence electrons much more firmly.  Where in the periodic table are the elements located that frequently lose valence electrons to become cations?  Sort the elemental data from low to high ionization potential (ascending sort). Which elements have the lowest ionization energy, and where are they found in the periodic table?  Which elements have the highest ionization energy, and where are they found?   

Discovering family similarities

Dimitri Mendeleev, a Russian chemist, created the first version of the Periodic Table of the Elements (figure 19.3) in 1869.  When he ordered the elements according to increasing atomic weight in columns so that rows contained analogous elements, he saw patterns that allowed him to predict the properties of elements yet to be discovered.   Mendeleev’s task was formidable because there was relatively little data to work with, and no electronic tools to organize it.  Today, however, we have an abundance of information as well as database tools that allow us to instantly group data by common characteristics.  Database technology has fueled the Information Revolution by allowing us to store and examine large amounts of data.  In this activity you will use a database program to separate data by groups and summarize your findings. 

Table 19.2 arranges the elements in terms of increasing atomic number.  No patterns or trends are seen when the elements are displayed in this fashion.  If, however, elements are arranged as seen in the periodic table, those with similar properties are grouped together.  Each column represents a family of elements that have similar electron configuration and similar chemical properties.  Although the periodic table makes it easy to see which elements have similar properties (those in the same family or column), it does not allow for an easy comparison of these properties.  By contrast, table 19.2 lists much specific information about the properties of the elements, but does not allow for comparison of family (group) data, unless first arranged by group.  

Sort the elements by group,  then calculate average group values for heat of fusion, specific heat, thermal conductivity, and other properties of your choice using the subtotal command and average option.  List your results.

(1) Which families are most similar to each other?

(2) Which families are most dissimilar to each other?