This unit covers chemical bonding, focusing on ionic and covalent compounds, their properties, and how they interact—especially in water. Below is a breakdown of each major concept.
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Part 1: Classifying Compounds
How to tell if a compound is ionic or covalent:
* Ionic compounds form between metals (+) and nonmetals (–). Electrons are transferred, creating ions (e.g., NaCl, CaCl₂).
* Covalent (molecular) compounds form between nonmetals only. Electrons are shared (e.g., H₂O, CO₂).
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Part 2: Writing Formulas
Ionic Compounds:
* Naming: Metal first, then nonmetal with "-ide" (e.g., sodium chloride = NaCl).
* Polyatomic ions: Groups like carbonate (CO₃²⁻) or hydroxide (OH⁻) stay together (e.g., potassium carbonate = K₂CO₃).
Covalent Compounds:
* Use prefixes (mono-, di-, tri-) to indicate atom counts (e.g., nitrogen trichloride = NCl₃).
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Part 3: Drawing Structures
Lewis Structures (Covalent Bonds):
* Show shared electron pairs as lines and lone pairs as dots.
* Example: CO₂ (O=C=O, linear, no lone pairs on carbon).
Ionic Structures (e.g., CaF₂):
* No sharing! Instead, ions in a lattice (Ca²⁺ surrounded by F⁻ ions).
Diatomic Molecules:
* 7 elements that exist as two-atom molecules in nature:
H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂ (BrINClHOF).
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Part 4: Electronegativity and Polarity
Polar vs. Nonpolar Bonds:
* Polar covalent: Electrons are unequally shared (e.g., H₂O, where oxygen pulls electrons harder).
* Nonpolar covalent: Electrons are equally shared (e.g., O₂, Br₂).
Determining Polarity:
* Check electronegativity difference:
* >1.7 = Ionic (electron transfer)
* 0.5–1.7 = Polar covalent (unequal sharing)
* <0.5 = Nonpolar covalent (equal sharing)
* Molecular shape matters too!
* Symmetrical molecules (e.g., CO₂) can be nonpolar even with polar bonds.
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Part 5: Water is Amazing!
Why is water polar?
* Oxygen is highly electronegative, pulling electrons away from hydrogen → partial charges (δ⁺ on H, δ⁻ on O).
Hydrogen Bonding:
* Weak attraction between δ⁺ H of one water molecule and δ⁻ O of another.
* Explains high boiling point, surface tension, and capillary action.
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Part 6: Comparing Ionic and Covalent Compounds
Properties:
Ionic
Covalent (Polar/Nonpolar)
High melting point
Low melting point
Conducts when dissolved
Nonconductive (except acids)
Soluble in water
Nonpolar = insoluble in water
Example Clues:
* White crystal that conducts when dissolved? Likely ionic (e.g., NaCl).
* Gas at room temp? Likely nonpolar covalent (e.g., O₂).
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Part 7: Molarity Math
Molarity (M) = moles of solute / liters of solution
* Example: If 4.5 moles of NaCl are dissolved in 3 L → M = 4.5/3 = 1.5 M.
* Conductivity depends on ions: More ions = better conductor (e.g., NaCl > sugar).
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Part 8: Science Sketches
1. Nonpolar Substance Melting:
* Weak London dispersion forces break easily when heated → particles move freely.
2. Ionic Dissociation in Water:
* Water molecules surround ions:
* Oxygen (δ⁻) faces positive ions (Na⁺).
* Hydrogen (δ⁺) faces negative ions (Cl⁻).
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Summary:
* Ionic = metal + nonmetal (electrons transferred).
* Covalent = nonmetals only (electrons shared).
* Polarity depends on electronegativity and shape.
* Water’s hydrogen bonding gives it unique properties.
* Molarity measures solution concentration.