✍️ Free Response Questions
AP Chemistry Free Response Questions
⚛️ Unit 1 - Atomic Structure and Properties
1.1Moles and Molar Mass
1.2Mass Spectroscopy of Elements
1.3Elemental Composition of Pure Substances
1.4Composition of Mixtures
1.5Atomic Structure and Electron Configurations
1.6Photoelectron Spectroscopy & Graph Interp.
🤓 Unit 2 - Molecular and Ionic Compound Structures and Properties
2.0Unit 2 Overview: Molecular and Ionic Bonding
2.1Types of Chemical Bonds
2.2Intramolecular Force and Potential Energy
2.3Ionic Bonding and Ionic Solids
2.4Metallic Bonding and Alloys
2.5Lewis Dot Diagrams
2.6Resonance and Formal Charge
🌀 Unit 3 - Intermolecular Forces and Properties
3.0Unit 3 Overview: Intermolecular Forces and Properties
3.2Properties of Solids
3.3Solids, Liquids, and Gases
3.4The Ideal Gas Law
3.5The Kinetic Molecular Theory of Gases
3.6Deviations from the Ideal Gas Law
3.7Mixtures and Solutions
3.8Representations of Solutions
3.9Separation of Solids/Mixtures
3.10Solubility and Solubility Rules
3.11Spectroscopy and the Electromagnetic Spectrum
3.12Quantum Mechanics and the Photoelectric Effect
🧪 Unit 4 - Chemical Reactions
4.0Unit 4 Overview: Chemical Reactions
4.1Recognizing Chemical Reactions
4.2Net Ionic Equations
4.4Physical vs. Chemical Changes
4.5Stoichiometry & Calculations
4.6Titrations - Intro and Calculations
4.8Intro to Acid-Base Neutralization Reactions
👟 Unit 5 - Kinetics
5.0Unit 5 Overview: Kinetics
5.1Defining Rate of Reaction
5.2Introduction to Rate Laws
5.3Rate and Concentration Change
5.4Writing Rate Laws
5.5Collision Model of Kinetics
5.6Reaction Energy and Graphs w/ Energy
5.7Reaction Mechanisms and Elementary Steps
5.8Writing Rate Laws Using Mechanisms
🔥 Unit 6 - Thermodynamics
6.0 Unit 6 Overview: Thermochemistry and Reaction Thermodynamics
6.1Endothermic Processes vs. Exothermic Processes
6.2Energy Diagrams of Reactions
6.3Kinetic Energy, Heat Transfer, and Thermal Equilibrium
6.4Heat Capacity and Coffee-Cup Calorimetry
6.5Phase Changes and Energy
6.6Introduction to Enthalpy of Reaction
6.7Bond Enthalpy and Bond Dissociation Energy
6.8Enthalpies of Formation
⚖️ Unit 7 - Equilibrium
🍊 Unit 8 - Acids and Bases
8.0Unit 8 Overview: Acids and Bases
8.1Introduction to Acids and Bases
Unit 9 - Applications of Thermodynamics
🤺 AP Chemistry Essentials
🧐 Multiple Choice Questions
AP Chemistry Self-Study and Homeschool
⏱️ 4 min read
August 23, 2020
When atoms interact with each other, they can form molecules. Depending on how the electrons of these atoms interact, a covalent bond or ionic bond would be formed. Atoms bond in order to reach a more stable, lower energy state.
The basics of bonding were explained in key topic 1.8.
Ionic bonds are formed by the transferring of electrons from atom to atom.
Na(s) + ½ Cl2(g) → NaCl(s)
NaCl, a brittle salt with a high melting point was formed in this chemical reaction. Ionic bonds are held together not by shared electrons or a direct bond, but rather through electromagnetic forces that hold positive and negative ions together. These electromagnetic forces are so strong that it takes lots of energy to break them apart, hence the high boiling and melting points. Ionic compounds also form a crystal lattice of ions, giving them their rigidity.
Coulomb's Law again states that greater charges and smaller distances lead to strongest attractions. Two factors that affect the melting point of ionic substances are those exactly: the charge of the ion and the size of the ion.
When asked which compound would have a higher melting point, always look for differences in charge and size. The higher the charge of the ion, the stronger the negative-positive attraction is and the more energy it takes to break the bond (therefore increasing the m.p.). Same goes for size!
💡Tip - Always look for differences in charge first; they have a greater impact on melting points.
Which ionic compound would have a higher melting point: LiF or NaBr?
Since both charges are the same (+1 / -1), the main difference would have to be the size of the ions. Keeping the periodic trends in mind, Lithium and Fluorine are much smaller ions than Sodium and Bromine**. Therefore, LiF must have the higher melting point.
Which compound would have a higher melting point: MgF2 or NaF.
Looking at charge first, you would notice that Mg has a +2 charge, while Na only has a +1 charge. This automatically means that MgF2 has a higher melting point than NaF.
**Lithium and Fluorine are in period 2, while Na is in period 3 and Br is in period 4. Remember, when you go down on the periodic table, the atomic radii increase since there are more occupied electron shells. You may be asked to give a reason for this trend in free response questions🤔!
In covalent bonding, electrons are shared between two or more atoms. There are two different types of covalent bonds.
If a polar covalent bond is formed, there is an unequal distribution of charge. If a nonpolar covalent bond is formed, there is an equal distribution of charge⚖️. We'll learn more about polarity when we get into molecular geometry later in this unit.
To analyze the difference between the two types of covalent bonds, we would need to look at electronegativity. Valence electrons shared between atoms of similar electronegativity constitute a nonpolar covalent bond (Ex/ O2 in the picture above). Since the electronegativity is the same, nuclei pull on the other oxygen atom's electrons with the same strength. Think: nonpolar = balance!
Valence electrons shared between atoms of unequal electronegativity constitute a polar covalent bond (Ex/ H2O). Hydrogen has an electronegativity of 2.2 while oxygen has an En of 3.44. Therefore, oxygen attracts electrons more strongly. This unequal distribution of charge leads to oxygen developing a partial negative charge. This difference in electronegativity leads to bond dipoles, which are covered more in the next unit.
For now, just remember that greater differences in En lead to greater bond dipoles!
Image Courtesy of Socratic
δ, or the lowercase delta, presents the partial positive or partial negative.
There are two ways you can guess which bond will form:
form between two elements that have an electronegativity difference of >1.7
usually form between a metal and a nonmetal
usually form between two nonmetals
Polar covalent bonds form between two elements that have an electronegativity difference of 0.4-1.7
Nonpolar covalent bonds form between two elements that are usually the same, but the en difference is usually between 0-0.4
If a solid has a high melting point and is a good conductor of heat and electricity when dissolved in water, it is most likely an ionic compound.
If a solid has a low melting point and doesn't conduct electricity in any state, it is most likely a molecular compound (which has covalent bonds).
There is one more circumstance:
If a solid has a high melting point and doesn't conduct electricity in any state, it is a network solid made up of covalent bonds. Don't worry about this yet, it's covered in future units :).
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