LAB #8: Periodic Properties of the Elements
Background:
The modern periodic table is organized by increasing atomic number in horizontal rows called periods. The rows are related to the principal energy levels of the electrons in their ground states for the atoms in that row. The vertical columns are called families or groups. The elements in a vertical column have similar chemical properties due to similarities in their valence electron configurations.
Atomic radii is one-half the distance from the nucleus of one atom to the nucleus of the next atom in the solid phase of an element. The radius of an ion may be smaller or larger than the atomic radius, depending upon the chemical nature of the atom.
The ionization energy of an element is the energy required to remove the most loosely held electron from a neutral atom of an element when it is in the gaseous phase.
Electron affinity is the energy released when a gaseous atom gains an electron.
Electronegativity is the tendency for an atom to attract electrons to itself when it is chemically combined with another element. Values are assigned based on various factors such as electron affinities and ionization energies. Electronegativities allow us to predict the polarity of bonds.
Purpose:
• To relate atomic structure to the organization of the periodic table and the reactivity of elements.
• To observe and explain the differences in reactivity of three elements of the alkali family (column IA) and two elements of the alkali earth metal family (column IIA).
• To observe the electron affinity of atomic oxygen.
PART I. The Organization of the Periodic Table:
A. Draw the electron configurations for the atoms on the blank periodic table. Highlight the commonalities between rows and columns.
B. Summarize the patterns observed on the smaller blank periodic table.
PART II. The Patterns in Electron Configurations:
1. Summarize the patterns observed in the columns of the representative elements.
What is the common electron configuration of the atoms?
How many valence electrons are in the last energy level?
IA / IIA / IIIA / IVA / VA / VIA / VIIA / VIIIA2. Describe the relationship between the columns and s, p, d, and f orbitals.
3. Describe the pattern observed in the rows. When does another row begin?
PART III. The Inert Gases in Column VIIIA:
4. Write the electron configurations of the six noble or inert gases.
a. What common electron configurations do all these atoms share?
Except helium- explain why it is still in this column?
b. These elements are generally unreactive and monoatomic. They seldom form bonds with other atoms. What can you conclude about the stability of these atoms? Explain.
c. What can be concluded about the stability of the other atoms(not in column VIIIA)? Use this to explain why the other atoms (not in column VIIIA) react and form bonds.
PART IV. Reactions of Elements in Column IA (alkali metals):
5. Lithium, sodium and potassium are all in column IA.
a. Based upon their location in this column, what can you conclude about the location of their last electron? (What is the same about these atoms?)
b. Based upon their location in different rows, what can you conclude about the location of their last electron? (What is different?)
c. Based upon the location of the last electron, are these atoms stable? Explain your reasoning.
d. What will these atoms do to become stable?
e. Will this process be associated with a transfer of energy in or out? Explain your reasoning.
6. Electrons are attracted to the nucleus.
a. What force attracts negative electrons to the positive protons in the nucleus?
b. This force depends on both charge and distance. (Coulomb’s Law)
c. Increasing the charge will result in ___ (more or less) force.
d. Increasing the distance will result in ___ (more or less) force.
e. Define ionization energy.
C. Predict which element will react the fastest with water: lithium, sodium, or potassium? Explain your thinking. Remember the reaction rate depends upon the frequency of effective collisions
D. Observe the reaction of lithium, sodium, and potassium (column IA) with water. Record your observations of the reactions.
7. Sodium reacts with water to produce sodium hydroxide and hydrogen gas.
a. What observation supports the formation of hydrogen gas?
b. What observation supports the formation of a basic solution? What ion is present in a basic solution?
c. Write the balanced equation for the reaction.
d. What happened to sodium atoms in the reaction? Draw the electron configuration before and after the reaction. Use stability and its electron configuration to explain why the sodium reacted in this manner.
e. Was sodium oxidized or reduced?
8. The water did not directly react with the metal added to the water. Instead an intermediate reaction was involved. The reversible reaction occurs in water all the time.
a. Describe what happened to the water molecules to form hydrogen and hydroxide ions. Include hat bond broke and how the sharing in this bond led to the formation of the negative hydroxide ion and positive hydrogen ion.
b. Write the equation for the reversible reaction.
c. What happened to the hydrogen ions to explain the formation of hydrogen gas? Include a half reaction to show the change. Was the hydrogen ion oxidized or reduced?
9. Use collisions between hydrogen ions and the metal to explain what happened in the reaction. Use the term effective collision and ionization energy in your explanation.
10. In addition to the sodium, lithium and potassium also reacted with the water.
a. Write the balanced equations for these reactions.
b. Lithium. Draw the electron configuration before and after the reaction. Explain the change based upon the electron configuration and stability. Write the half-reaction.
c. Potassium. Draw the electron configuration before and after the reaction. Explain the change based upon the electron configuration and stability. Write the half-reaction.
11. Lithium, sodium and potassium were all oxidized when they reacted with water.
a. List the elements from least reactive to the most reactive. Support with your observations of the reactions.
b. Explain the difference in reactivity based upon the location of the last electron in each element. Use effective collisions, ionization energy and electrical force in your explanation.
12. All the reactions were exothermic.
a. Support this claim with evidence from your observations of the reaction.
b. The energy content increases or decreases in the reaction? The net change in energy is therefore positive or negative?
c. Which metal will have the greatest activation energy on the energy graph? Relate this to the rate of the reaction.
d. Sketch an energy graph for each reaction to show the change in energy.
PART V. Reactions of Elements in Column IIA(alkali earth metals):
E. Predict whether calcium or magnesium will react faster with water. Explain your reasoning.
F. Predict whether calcium or potassium will react faster with water. Explain your reasoning.
G. Observe the reaction of magnesium and calcium (column IIA) with water.
Record your observations of the reactions.
13. Compare the reaction of potassium (from IA) and calcium (from IIA) with water.
a. Explain why potassium loses one electron in the reaction with water, while calcium loses two electrons. Include stability and the locations of electrons in orbitals to explain.
b. Based upon your observation of the reactions, which reacts faster with water: potassium or calcium? Which reaction must have a lower activation energy? Explain your reasoning using effective collisions.
c. Which metal must have a lower first ionization energy? Explain based upon electrical force and the location of the last electron.
14. Compare the reaction of magnesium and calcium with water.
a. Which metal reacted faster?
b. Does this fit with your prediction? Explain any changes you need to make in your thinking.
c. Draw the electron configuration of each atom. Explain why they both lose two electrons.
15. Recall the previous reactions with sodium, magnesium and aluminum.
a. Remember each of these metals was placed in water. Which was the most reactive with water? Explain this prior observation now in terms of their electron configurations.
b. Remember that both magnesium and aluminum were added to hydrochloric acid. Compare the reactivity of magnesium and aluminum with hydrochloric acid. Explain this prior observation now in terms of their electron configurations.
PART VI. The Reactivity of Oxygen from Column VIA:
E. Describe the reactivity of atomic oxygen. Describe your observations of the reaction.
16. Draw the electron configuration of the atomic oxygen.
What happened to the oxygen atom to become stable?
17. Draw the electron configuration of the oxygen molecule. What kind of bond holds together the two atoms in the oxygen molecule?
18. Explain the reaction. What happened? What was the form of the oxygen before and after the reaction? When was it more stable? Why was it so reactive?
PART VII More Patterns on the Periodic Table:
19. Atomic Radii.
a. Within a period (horizontally), what happens to the radii of the atoms? Explain why.
b. Within a family (vertically), what happens to the radii of the atoms? Explain why.
c. Explain the effect on the radius of an atom when an ion is formed. Relate the ionic radii of the metals and nonmetals to what happened to the electrons.
20. Ionization Energy.
a. Within a period (horizontally), what happens to the ionization energy of the atoms? Explain why. Support with evidence.
b. Within a family (vertically), what happens to the ionization energy of the atoms? Explain why. Support with evidence.
21. Electron Affinity and Electronegativity.
a. Within a period (horizontally), what happens to the electronegativity of the atoms?
Explain why.
b. Within a family (vertically), what happens to the electronegativity of the atoms?
Explain why.
Conclusions:
Explain why atoms react to form bonds with other atoms. Use electron configuration and stability in your explanation.