Unit 3 Lesson 1: Investigating Chemical Compounds
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Chemistry: Unit 3, Lesson 1
Unit 3: Compounds and Mixtures
Lesson 1: Investigating Chemical Compounds
Phenomenon: Sodium and Chlorine Reaction
Observation: Sodium metal is exposed to chlorine gas.
Prediction: How do you think the properties of sodium and chlorine change when they are combined to make sodium chloride?
Sodium chloride (left) is the product of the reaction of sodium metal (center) and chlorine gas (right).
Analyzing the Properties of Compounds
Research Question: How does a compound's atomic-level structure influence its use in natural or human-designed systems?
Sodium metal, chlorine gas, and sodium chloride have different properties.
Conclusion: What can you conclude about the forces holding the atoms of these substances together?
What tests could you run to learn more about each substance?
Describing Chemical Bonds
Analogy: Systems tend to naturally change toward lower, more stable energy states, like a ball rolling down a hill.
Potential energy converts to kinetic energy as the ball rolls down to a more energetically stable position.
Chemical bond formation leads to more stable energy states.
Electronegativity: A measure of the tendency of an atom to attract electrons.
Differences in electronegativity predict the types of chemical bonds atoms will form.
Patterns in electronegativity are observed on the periodic table.
Ionic Bond: Formed by the transfer of one or more electrons.
A greater difference in electronegativity corresponds to a more complete transfer of electrons from one atom to the other.
Covalent Bond: As the electronegativity difference decreases, atoms share valence electrons.
Soap Scum: When soaps are used in hard water, ions like calcium or magnesium form soap scum.
Soap scum contains insoluble compounds like magnesium stearate, .
Question: What bond types are present in magnesium stearate? How might bond type explain the properties of the soap you are investigating in your unit project?
Describing Chemical Bonds - Salts
Lithium salts are isolated by solar evaporation of water from brine.
Salts are ionic compounds made of metal and nonmetal ions.
Salts are important for human life and activities.
Salts can be mined from deposits left by natural evaporation of ancient oceans.
As the water evaporated, the ions in solution formed new ionic bonds, producing a crystalline ionic compound.
Salts can also be produced by evaporating water from seawater.
Describing Chemical Bonds - Covalent Bonds
Covalent Bond: Neither atom exerts sufficient attractive force to cause an electron to transfer, so electrons are shared.
Molecule: A neutral group of atoms held together by covalent bonds.
A fluorine molecule is shown in the diagram.
Describing Chemical Bonds - Hands-On Lab
Analyze conductivity, solubility, and melting point to determine the bonding type present in solids.
Describing Chemical Bonds - Metallic Bonding
Metallic Bonding: Chemical bonding that results from the attraction between metal atoms and the surrounding sea of electrons.
A metal spoon can complete a circuit because the delocalized electrons move when a current is applied.
Question: What types of bonds form within a sample of sodium metal, chlorine gas, and sodium chloride crystals? How does the electron structure of each substance affect the properties of compounds that it forms?
Predicting the Structure of Compounds
Research other compounds formed when Group 2 and Group 17 atoms combine.
What do you notice about the ratio of atoms in the compound? How many bonds form, and what types of bonds?
Do other groups, like Group 1 and Group 16, show a pattern when their atoms combine?
Ionic Bond Formation: Metal atoms transfer electrons to nonmetal atoms.
A nonmetal atom accepts enough electrons to fill its outer shell, and a metal atom loses enough electrons to empty its outer shell.
This transfer determines the ratio of the elements in the ionic compound.
Chemical Formula: Indicates the relative numbers of atoms of each element in the compound, using atomic symbols and subscript numerals.
In calcium fluoride, the simplest unit contains a ratio of two fluoride ions to one calcium ion.
Predicting the Structure of Compounds- Patterns
The table shows chemical formulas for binary ionic compounds (containing one metal and one nonmetal element) from Period 3 of the periodic table.
How does the placement of the elements on the periodic table appear to relate to the numbers in the chemical formula?
Predicting the Structure of Compounds- Language Arts Connection
Elements in Group 17 (halogens) are highly reactive, whereas elements in Group 18 (noble gases) have very low chemical reactivity.
Research these two groups of elements to explain the difference in reactivity.
How do the valence electron patterns in these groups affect how elements in each group are used?
Write a summary report, including a full list of sources.
Predicting the Structure of Compounds- Math Connection
Crisscross Method: A shortcut for determining the formula of an ionic compound.
The charge for each ion becomes the subscript for the other ion in the formula.
Polyatomic Ion: A group of covalently bonded atoms that has a charge and behaves as an ion.
To determine the chemical formula for compounds containing a polyatomic ion, follow the same rules about making the compound neutral as with a single-atom ion.
Predicting the Structure of Compounds- Carbon Tetrafluoride
Model the structure of carbon tetrafluoride, a low-temperature refrigerant and greenhouse gas (one carbon atom and four fluorine atoms).
How many valence electrons are present in carbon and fluorine, and how are they shared in carbon tetrafluoride?
How many bonds are present? Why are the bonds considered covalent?
How does your model show that all the atoms in carbon tetrafluoride obtain octets by sharing electrons?
Evidence Notebook Determine the chemical formulas for sodium metal, chlorine gas, and sodium chloride. How can you use the electron-dot structures of chlorine gas and sodium metal to predict their reactivity levels and the compound they form when they react?
Modeling the Shapes of Molecules
Research Question: What shapes can molecules take on, and why is this important in understanding the behavior of substances?
How do valence electrons in sodium chloride determine its structure as an ionic compound? How does that compare to the valence electrons in the molecular structures you investigated in this lab?
Continue Your Exploration
Choose one of the paths below to continue your exploration:
Asking Questions about Minerals
More Practice with Formulas
Hands-On Lab: Types of Bonding in Solids
Teaching Types of Bonding
Can You Explain the Phenomenon?
Refer to your notes in your Evidence Notebook to explain why sodium metal and chlorine gas are dangerous and reactive on their own but combine to form the stable compound sodium chloride.
Your explanation should include a discussion of the electrical forces within and between atoms in each substance.
Claim: Make a claim about why the compound sodium chloride has properties that are so different from the properties of sodium and chlorine.
Evidence: What evidence supports your claim? For example, what differences in chemical structure could explain the differences in reactivity among the three substances?
Reasoning: Explain how the evidence you gave supports your claim about why sodium chloride is different from sodium metal and chlorine gas.