Download File

Periodic Trends Lesson (2-Day)
By Erik Haigler
Day1
Purpose
a. Students will be able to identify the trends of the periodic table
b. Students will be able to understand the concepts of each periodic trend
c. Students will be able to explain how the trend increases or decreases across and up and
down the periodic table
d. Students will be able to show and understand how understanding the concept and trend
are connected
Virginia S.O.L’s
CH.2
The student will investigate and understand that the placement of elements on the
periodic table is a function of their atomic structure. The periodic table is a tool used
for the investigations of
d) families or groups;
e) periods;
f) trends including atomic radii, electronegativity, shielding effect, and ionization
energy;
Materials
• Periodic Table
• Alien Cards
• March Madness Bracket
Science Safety
Students should be cleanup table at the end of class and throw all trash away in the nearest trash
can. No Horseplay!
Procedure
Engage (5 minutes)
Show video and highlight the key points made about properties and trends.
https://www.youtube.com/watch?v=O-48znAg7VE#t=226
Explore (20 minutes)
Reconnect to the Alien Periodic table, but this time instead of focusing on the table layout focus
on trends between the aliens. Draw a connection on how the trends between the aliens and the
trends between the elements are not that different.
Experiment Overview: In cooperative activity, you will use the 40 cards and construct an Alien
Periodic Table. You will arrange the Aliens in some logical pattern so that they form an
organized regular block. The resulting table is visually impressive and clearly the meaning of
periodic trends.
Questions:
1. What multiple trends (Key Similarities and Varying Traits) did you use to distinguish the
eight families?
2. What multiple trends (Key Similarities and Varying Traits) did you use to distinguish the
five periods?
3. What is at least one trend that you already know on the periodic table?
4. Try to name at least 3 other trends you might know or make up three others?
5. Draw the missing alien from your periodic table!
Explain (10-15 minutes)
The following trends will be briefly covered and students will take notes then students will draw
how the trend moves across period and group on their own periodic table
Effective nuclear charge
The effective nuclear charge is the net positive charge experienced by an electron in a multielectron atom. The term "effective" is used because the shielding effect of negatively charged
electrons prevents higher orbital electrons from experiencing the full nuclear charge by the
repelling effect of inner-layer electrons. The effective nuclear charge experienced by the outer
shell electron is also called the core charge. It is possible to determine the strength of the nuclear
charge by looking at the oxidation number of the atom.
- Increase across a period (due to increasing nuclear charge with no accompanying increase
in shielding effect).
- Decrease down a group (although nuclear charge increases down a group, shielding effect
more than counters its effect).
Atomic Radius Trends
For atoms, the atomic radius is one-half the distance between the nuclei of two atoms is (just like
a radius is half the diameter of a circle). However, this idea is complicated by the fact that not all
atoms are normally bound together in the same way. Some are bound by covalent bonds in
molecules, some are attracted to each other in ionic crystals, and others are held in metallic
crystals. Nevertheless, it is possible for a vast majority of elements to form covalent molecules in
which two like atoms are held together by a single covalent bond. The covalent radius of these
molecules is often referred to as the atomic radius. This distance is measured in picometers.
Going through each of the elements of the periodic table, patterns of the atomic radius can be
seen.
- Atomic radius decreases from left to right within a period. This is caused by the increase
in the number of protons and electrons across a period. One proton has a greater effect
-
than one electron; thus, a lot of electrons will get pulled towards the nucleus, resulting in
a smaller radius.
Atomic radius increases from top to bottom within a group. This is caused by electron
shielding.
Ionization Energy Trends
Ionization Energy is the amount of energy required to remove an electron from a neutral atom in
its gaseous phase. Conceptually, ionization energy is considered the opposite of
electronegativity. The lower this energy is, the more readily the atom becomes a cation.
Therefore, the higher this energy is, the more unlikely the atom becomes a cation. Generally,
elements on the right side of the periodic table have a higher ionization energy because their
valence shell is nearly filled. Elements on the left side of the periodic table have low ionization
energies because of their willingness to lose electrons and become cations. Thus, ionization
energy increases from left to right on the periodic table.
Another factor that affects ionization energy is electron shielding. Electron shielding describes
the ability of an atom's inner electrons to shield its positively-charged nucleus from its valence
electrons.
- The ionization energy of the elements within a period generally increases from left to
right. This is due to valence shell stability.
- The ionization energy of the elements within a group generally decreases from top to
bottom. This is due to electron shielding.
Elaborate (30 minutes)
March Madness is upon us! Your students are probably already working on their next assignment
in bracketology, predicting the field for the NCAA Basketball Tournament.
Let’s apply the principles of bracketology to the properties of the elements. The competition
among the 64 elements is stiff, and there is a wealth of information for students to research, in
this “elementary” version of March Madness!
Define each of the following properties of the elements and briefly describe any periodic trend in
the property across a row or down a column in the periodic table.
- Ionization energy, Atomic radius, Effective nuclear charge
Evaluate (10 minutes)
I will actively evaluate students throughout the bracket exercise. After I will give students an exit
slip where they will have give me a definition in their own words of the each trend and be able to
draw each trends arrow on a periodic table.
Day 2
Purpose
a. Students will be able to identify the trends of the periodic table
b. Students will be able to understand the concepts of each periodic trend
c. Students will be able to explain how the trend increases or decreases across and up and
down the periodic table
d. Students will be able to show and understand how understanding the concept and trend
are connected
Virginia S.O.L’s
CH.2
The student will investigate and understand that the placement of elements on the
periodic table is a function of their atomic structure. The periodic table is a tool used
for the investigations of
d) families or groups;
e) periods;
f) trends including atomic radii, electronegativity, shielding effect, and ionization
energy;
h) chemical and physical properties; and
Materials
• Periodic Table
• Think Pair Share Activity Sheet
• 1 die for each group
• Index cards with main group element symbols
• Periodic Trend War Activity Sheet
Science Safety
Students should be careful not to lose any of the elements cards or other material used in the
game. When finished student should return all items back to the station bucket in which they
were found. Students should be cleanup table at the end of class and throw all trash away in the
nearest trash can. No Horseplay!
Procedure
Engage (5 minutes)
Show video http://education-portal.com/academy/lesson/electronegativity-trends-among-groupsand-periods-of-the-periodic-table.html#lesson
Explore (5 minutes)
Students will play a tug of war game and show how the number of valence electrons creates a
high electronegativity by adding more students for each electron.
Explain (10 minutes)
The following trends will be briefly covered and students will take notes then students will draw
how the trend moves across period and group on their own periodic table
Electron affinity
Like the name suggests, electron affinity describes the ability of an atom to accept an electron.
Unlike electronegativity, electron affinity is a quantitative measure that measures the energy
change that occurs when an electron is added to a neutral gas atom. When measuring electron
affinity, the more negative the value, the more of an affinity to electrons that atom has.
- With Electron affinity increases from left to right within a period. This is caused by the
decrease in atomic radius.
- Electron affinity decreases from top to bottom within a group. This is caused by the
increase in atomic radius.
Chemical Reactivity
METALS
 DOWN a Group: In METALS reactivity INCREASES as you go DOWN a Group
because the farther down a Group of metals you go, the easier it is for electrons to be
given or taken away, resulting in higher reactivity.
 ACROSS a Period: In METALS reactivity DECREASES as you go ACROSS a Period
because though they still want to give away valence electrons they have more of them to
get rid of, which requires more energy. Not as easy to blow off a little steam!
NON-METALS
 UP a Group: In NON-METALS reactivity INCREASES as you go UP a Group because
the higher up and to the right atoms are, the higher the electronegativity, resulting in a
more vigorous exchange of electrons. Fluorine? A greedy, impatient beast when it comes
to electron exchange manners.
 ACROSS a Period: In NON-METALS reactivity INCREASES as you go ACROSS a
Period because (notice how trends repeat?) the closer you get to filling your s- and porbital’s the more motivated you are to do so.
Show Cool video of this in action
https://www.youtube.com/watch?v=uixxJtJPVXk
Elaborate (20 minutes)
Think Pair Share Reactivity Video Lab
Students are to write down what they thing about the periodic trends, reactivity, then get with
partners to discuss
Show Cool video of this in action https://www.youtube.com/watch?v=uixxJtJPVXk and then get
students to discuss what they saw and how it alters their views.
Evaluate (50 minutes)
Periodic Table Trend War
Purpose: To teach students periodic trends regarding the properties of elements.
Materials: 1 die, index cards with main group element symbols written on them (one element per
card), a list of trends written on the board numbered from 1 -6. Trends should include such
things as ionization energy, electronegativity, atomic radius, electron affinity, reactivity etc... A
"wild" category can be included which allows the roller of the dice to choose the trend.
Quiz will follow on all trends