Bond Types & Physical Properties Station Data Lab Sheet
Name ____________________________________________ Period/Block _________ Date _______________________
Objective: Elements are not usually found alone in nature. Rather, a chemical bond may form between two or more elements to make a compound. Compounds can be characterized as ionic, covalent or metallic. In this lab, you will explore the characteristics of 3 major types of bonds: ionic bonds, covalent bonds (molecular covalent & network covalent) and metallic bonds. Procedure: Visit each station and perform the following. 1. Read the directions provided on each station card. 2. Perform the procedure as indicated. 3. Make careful observations for the covalent, metallic and ionic substances. 4. Write a claim as well as the evidence used to support that claim which explains how ionic, covalent and metallic compounds are similar or different.
Definition of claim and evidence
Example sentence starters
Claim: A statement of what is true or believed to be true
It was determined that _________________
Evidence: Facts obtained from an experiment that relate to and support the claim
The evidence that supports this claim is____________
Stations #1 & 2: Solubility and Conductivity Background Information Solubility is the ability of a substance to dissolve in another substance. Determine if the provided substances are soluble in water. Conductivity is the ability for a substance to conduct electricity. If compounds produce ions in water (aqueous), then they will conduct electricity. Determine whether a substance conducts electricity by placing the conductivity tester in solution. Lights up BRIGHTLY = STRONG conductor;
Lights up DIMLY = WEAK conductor; DOES NOT light up = DOES NOT conduct electricity
Observations Substance(s)
Bond Type
Dissolves in Water (Yes or No)
Conducting Ability of Solution (Strong, Weak or None)
Conducting Ability of Dry Substance (Strong, Weak or None)
Ionic Ionic Molecular covalent Molecular covalent Network covalent Network covalent Metallic Metallic Claim
Evidence
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Graphic modified from Living by Chemistry, First Edition, Angelica Stacy, 2010 Key Curriculum Press, Page 133.
Do not conduct electricity
Do conduct electricity
Do conduct electricity (dry solids)
Do not conduct electricity (dry solids)
Stations #3 & 4: Crystal Structure & Brittleness/Hardness Background Information Crystal structures form from the interaction of positive ions (cations) and negative ions (anions). Observe substances under a magnifying glass & record observations. Certain bonds tend to form brittle structures. A substance is brittle, if it is hard and fractures into many pieces when it does break. To test brittleness, place a micro amount of each sample into the mortar. Gently grind with pestle and observe. If it is brittle, it should make a noise as it fractures into pieces. If it powders easily, record it as being soft. Repeat with each of the samples. CLEAN when finished (place solids into waste bins)
Observations Substance(s)
Bond Type
Crystalline Structure (Observations)
Hardness (Soft, Hard, Brittle)
Ionic Molecular covalent Network covalent Metallic Claim
Evidence
Graphic from Living by Chemistry, First Edition, Angelica Stacy, 2010 Key Curriculum Press, Page 132.
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Stations #5 & 6: Melting points Background Information Melting point is the temperature at which a solid becomes liquid. Certain types of compounds tend to have higher melting points than others. The MelTemp is set at a temperature of 200⁰C or less. If the substance melts quickly at this temperature, record the melting point as low. If it does not melt, record the melting point as high. Also use Chart 1 from Station 6 to justify your claim. Observations Claim Substance(s)
Bond Type
Melting Point (Low or High)
Ionic Ionic Molecular covalent Molecular covalent
Evidence
Comparing Melting Points for Network Covalent & Metallic Substances with the Two Types Listed Above. (Chart 2 from Station 6) Claim Evidence
Station #7: Component of compounds: Metals or Non-metals Background Information Sometimes the bond type can be determined by looking at the types of elements in a substance. To determine the type of bond in a substance, analyze whether a nonmetal is bonded to a nonmetal (NM-NM) or a metal is bonded to a nonmetal (M-NM) or a metal is bonded to a metal (M-M). Observations Claim Substance
Bond Type
Components (NM-NM or M-NM or M-M)
NaCl
Ionic
MgBr2
Ionic
CuSO4
Ionic
NaF
Ionic
Benzoic acid, C7H6O2
Molecular covalent
PO4
Molecular covalent
H2O
Molecular covalent
CO2
Molecular covalent
Copper metal, Cu
Metallic
Iron metal, Fe
Metallic
Evidence
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Station #8: Differences in Electronegativity Values Background Information Electronegativity is a measure of how strongly atoms attract bonding electrons to themselves. Compounds may be characterized by analyzing the electronegativity differences between the elements making up the compound. Subtract the two electronegativity values from each other. (Ignore subscripts when you subtract.) For example: CaCl2 - Ca: EN 1.00 Cl: EN 3.16 The difference is 3.16-1.00= 2.16 Which element has the smallest electronegativity value (the least “pulling power”)? ___________________ Which element has the largest electronegativity value (the most “pulling power”)? ___________________
Observations Substance
Claim Bond Type
NaCl
Ionic
MgBr2
Ionic
CaO
Ionic
NaF
Ionic
Cl2 (Cl-Cl)
Molecular covalent
PO4
Molecular covalent
H2O
Molecular covalent
CO2
Molecular covalent
Electronegativity Difference
Evidence
Station #9: Comparing Four Models of Bonding Background Information Each sphere in the drawing represents an atom. The gray shaded areas represent places where the negatively charged valence electrons might be found with each type of bond. Graphics from Living by Chemistry, First Edition, Angelica Stacy, 2010 Key Curriculum Press.
Examples of Substances (from sorting cards) Ionic
Molecular Covalent
Metallic
Network Covalent
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Station #10: Developing a Model: The Bond-Type Triangle Background Information Electronegativity (EN) refers to the “pulling power” that an atom has for electrons. The larger the EN value, the greater the ability of the atom to attract electrons. Calculate the average electronegativity (AvgEN) and the absolute difference in electronegativity (EN) for the bonds in the substances listed. Electronegativity (EN) Substance AvgEN Type of Bonding EN First Atom Second Atom CsF (s) 0.7 4.0 Ionic KBr (s) 0.8 2.8 Ionic NaCl (s) 0.9 3.0 Ionic Cs (s) 0.7 0.7 Metallic Mg (s) 1.2 1.2 Metallic Al (s) 1.5 1.5 Metallic F2 (g) 4.0 4.0 Covalent CO (g) 2.5 3.5 Covalent C (diamond,s) 2.5 2.5 Covalent 1) Based on the data from the chart above what type of bonding resulted from the following combinations? Medium AvgEN and High EN __________________ Low AvgEN and Low EN ______________________ High AvgEN and Low EN ______________________ 2) In the space to the right, plot each of the substances on a graph of AvgEN (x-axis) versus EN (y-axis). Label each point with the type of bonding represented by each substance. 3) Use the points for the substances CsF, F2 and Cs to generate a triangle on the graph. Why were these points chosen to make the triangle? (Refer to questions from Station 8.) _____________________________________________________ Note: The types of bonds involved between atoms are usually not this easily identified. Many compounds have properties that are intermediate between the three bond types.
Station #11: Using a Model: The Bond-Type Triangle Background Information 1) In covalent bonding, sometimes electrons are more attracted to one nucleus than another. This results in a bond where electrons are not equally shared called a polar covalent bond. In what region on the Bond-Type Triangle would you find substances with polar covalent bonding? Explain your reasoning. _________________________________________________________________________________ 2) Some substances, called semimetals or metalloids, have metallic bonds where the electrons are more tightly held. These substances have fewer metallic properties and more covalent properties. In what region on the Bond-Type Triangle would you find metalloids? List one example of a metalloid. _________________________________________________________________________________________ 3) Use the Bond-Type Triangle to determine if the bonding of these substances is ionic, metallic, semi-metallic, covalent or polar covalent.
Substance H20 (g) KF (s) Si (s) O2 (g) FeC (s) Pb (s) Cl2 (g) CaS (s)
Electronegativity (EN) First Atom Second Atom 2.2 3.5 0.82 3.98 1.9 1.9 3.44 3.44 1.83 2.55 2.33 2.33 3.16 3.16 1.00 2.58
AvgEN
EN
2.85 2.4 1.9 3.44 2.19 2.33 3.16 1.79
1.3 3.16 0 0 0.72 0 0 1.58
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Type of Bonding
Post-Experiment Questions: 1. Compare and contrast the solids in terms of their a) Ability to dissolve in water. b) Ability to conduct electricity while in water. c) Shape.
d) Hardness. e) Melting behavior.
2. Describe any patterns you identify among these solids?
3. The composition of six other solids is as follows. Refer to your Periodic Table. How can you classify the elements found in the six solids with respect to the periodic table? What type of bond exists between the elements? a) b) c) d) e) f)
Solid A is composed of K and Cl. Solid B is composed of Mg and O. Solid C is composed of C, H, and O. Solid D is composed of C, and H. Solid E is composed of Zn. Solid F is composed of Ag.
4. Name two other pairs of elements that might form a compound that is both hard and dissolves in water.
5. A compound has the chemical formula C6H12O6. What physical properties would you expect it to have? Why?
6. Why might one solid be harder to crush than another solid? 7. Why might one solid more readily melt than another solid? 8. Using grammatically correct sentences, answer the following essential questions. a. How can ionic, covalent, and metallic compounds be classified by their physical properties?
b. How can one determine if a bond between two atoms is ionic, covalent, or metallic?
c. How does atom electronegativity affect bond character?
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ELABORATE
Analysis of data for everyday substances and determine the main type of bond involved. 1.
A student pours a packet of powdered sports drink into a glass of water and stirs it until it has all dissolved. He reads that the solution contains electrolytes and that it will conduct an electric current. What is the main type of chemical bond in the powdered sports drink? Justify your answer with evidence.
2.
A student buys some rock candy and notices its pretty crystalline structure. She decides to perform a few simple tests on the rock candy. She observes that it does dissolve in water but that the solution does not conduct an electric current. What is the main type of chemical bond in the rock candy? Justify your answer with evidence.
3.
A student has a bracelet that has the word “silver” embossed on the inside of it. What data could she analyze to determine the chemical bond involved is metallic?
Concept Map
Draw a final concept map relating all the terms mentioned in the Bond Types lab.
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