Are There Property Patterns?
Introduction
Chemists often look for patterns in the properties of different tested
materials in order to predict the properties of untested samples. For
example, it seems plausible to imagine that substances containing “lighter”
molecules or atoms will melt at lower temperatures than substances made
up of “heavier” atoms or molecules. The chemist will test this idea by
determining whether a set of samples exhibit a mass and melting-point
pattern and, based on results, will either refine or discard the idea. In this
investigation, your team will test ideas relating atomic or molecular
structure and a property. Your task is to identify groups of substances
where the correlation works and explore possible reasons for its failure
when it doesn’t.
Procedures
This inquiry asks you to use the Internet, chemical reference books, and text books
to obtain and plot property data about samples..Internet Web sites such as
webelements at www.webelements.com are available that allow one to determine
or plot properties of the elements against atomic structure.
Part I – Properties and Atomic Number
Guidelines
Full table charts. Answer the following questions based on any noticeable trends
in melting points.
1.
Is there a general trend in the property as atomic number increases?
2.
Is there an observable property pattern across a period of elements?
3.
Is there an observable property pattern down a group of elements?
4.
Does the data support your hypothesis?
Atomic Radius Patterns
6-2 Atomic Radii (Whitten, Page 222 – 223)
For all practical purposes, the size of an individual atom __________ be
uniquely defined. An indirect approach is required. The size of an atom
is determined by its immediate _____________, especially its interaction
with surrounding ___________. ______________ __________ of many
elements can be calculated from known ________________ of each atom.
We derive atomic radii from the observed ______________ between
atoms that are combined with one another. Basically, the atomic radius is
the radius of an atom.
1. Why is the Effect Nuclear Charge less in outer shell electrons than that of
inner shell electrons?
2. Hypothesis… Do you expect to observe a general trend in the atomic
radius of elements as the atomic number of elements increases? Record
your hypothesis.
3. Go back to the homepage using the WebElements tab at the bottom left.
On the homepage, click on Periodicity. Look on the right side of the
webpage and find Atomic Properties. Under Atomic Properties, click on
Atomic Sizes. View a Ball chart of atomic radius versus atomic number.
a. Is there a general trend in the property as atomic number increases?
b. Is there an observable property pattern across a period of elements?
c. Is there an observable property pattern down a group of elements?
d. Does the data support your hypothesis?
4. On the left side of the webpage, select periods 2, 3, 4, 5spd, and 6 to view
the plots and look for patterns of the main group elements, as well as the
transition elements. Explain the trend.
Electronegativity Patterns
1.
Density Patterns
1. Go back to the homepage using the WebElements tab at the bottom left. On the
homepage, click on Periodicity, scroll down, then click on Density. Record the
definition for Density.
2. Hypothesis…Do you expect to find a general trend in the density of elements as
atomic number increases? Record your hypothesis.
3. View all of the charts of density versus atomic number listed under the graph.
Answer the following questions based on trends in density and atomic number.
a. Is there a general trend in the property as atomic number increases?
b. Is there an observable property pattern across a period of elements?
c. Is there an observable property pattern down a group of elements?
d. Does the data support or contradict your hypothesis?
2.
3.
4.
5.
6.
7.
Go back to the homepage using the WebElements tab at the bottom left.
On the homepage, click on Periodicity. On the right side of the webpage,
scroll down and click on the word Pauling. Record the definition of
Pauling Electronegativity.
Hypothesis… Do you expect a general trend in the electronegativity of
elements as atomic number increases? Record your hypothesis.
View a bar plot of electronegativity versus atomic number from among
the choices found at the bottom of the chart. Record any noticeable
trends.
On the left side of the webpage, select periods 2, 3, and 4. Record any
electronegativity patterns within the periods of the main and transition
group elements.
On the left side of the webpage, select groups 1, 2, 13, 14, 15, 16, and 17.
Record any electronegativity patterns within the families (groups) of the
main group elements.
Does the data support or contradict your hypothesis?
Give the names of Groups 1, 2, 17, and 18.
Ionization Energy Patterns
1.
2.
3.
4.
Go back to the homepage using the WebElements tab at the bottom left. On
the homepage, click on Periodicity, scroll down, then click on Ionization
Energy. Record the definition for Ionization Energy. Click on First Ionization
energy and record that definition as well.
Hypothesis…Do you expect to find a general trend in the First Ionization
Energy of elements as atomic number increases? Record your hypothesis.
View all of the charts of Ionization energy versus atomic number listed under
the graph. Answer the following questions based on trends in Ionization
energy and atomic number.
a. Is there a general trend in the property as atomic number increases?
b. Is there an observable property pattern across a period of elements?
c. Is there an observable property pattern down a group of elements?
Does the data support or contradict your hypothesis?
Electron Affinity
1.
2.
3.
4.
5.
6-4 Electron Affinity (Whitten, Page 227 - 228)
Electron affinity is the amount of energy __________________ when an
electron is ______________ to an isolated gaseous atom to form an ion with a
-1 charge.
Elements with very _______________________ electron affinities gain
electrons easily to form negative ions ( ____________).
Hypothesis…Do you expect to find a general trend in the Electron affinities of
elements as atomic number increases?
View all of the charts of Electron Affinities versus atomic number listed under
the graph. Answer the following questions based on trends in Electron
Affinity and atomic number.
a. For the main group elements, is there a general trend in the property as
atomic number increases?
b. Is there an observable property pattern across a period for the main group
elements?
c. Is there an observable property pattern down a group for the main group
elements?
d. Does the data support or contradict your hypothesis?
Ionic Radii
1.
2.
3.
Go back to the homepage using the WebElements tab at the bottom left. On
the homepage, click on Periodicity, scroll down, then click on Ionic Radius
(Pauling).
Hypothesis…Do you expect to find a general trend in the Ionic Radii of
elements as atomic number increases? Record your hypothesis.
View all of the charts of Ionc Radii versus atomic number listed under the
graph. Answer the following questions based on trends in Ionic radii and
atomic number.
a.
b.
c.
d.
For the main group elements, is there a general trend in Ionic Radii as
atomic number increases?
Is there an observable property pattern across a period for the main
group elements?
Is there an observable property pattern down a group for the main
group elements?
Does the data support or contradict your hypothesis?
Data Analysis and Implications
On your periodic table you colored, draw the appropriate arrows for each of the
trends.
 As you go up or down a group ( ↑, ↓ ), draw an arrow depicting the
general
trend for each property as that property increases.
 As you go left or right across a period ( →, ← ), draw an arrow depicting
the
general trend for each property as that property increases.
 Focus on the Main Group elements only.
 Be sure to label the trends clearly on the periodic table.
Trends :
Melting Point
Density
Atomic Radius
Electronegativity
Ionization energy
Electron Affinity
Ionic Radii