🧪AP Chemistry
Verified for the 2025 AP Chemistry exam•7 min read•Last Updated on June 18, 2024
Atoms come together to make molecules, right? What terms would you use for the two specific atoms that make up an ionic solid? The words you use can make or break your FRQ response, so make sure you are careful!
Ionic solids are made up of a positive cation and a negative anion. Ionic bonding typically occurs when a metal's valence electron is transferred to a nonmetal. Since the metal loses a negative electron, it becomes a cation. On the other hand, since the nonmetal gains a negative electron, it becomes an anion.
The positive cation and negative anion interact because of their opposite charges, but how much they interact depends, again, on Coulomb's Law.
As mentioned earlier, ionic interactions can produce brittle, hard solids that have high melting points. This is due to the ions being held in a 3-D array known as a crystal lattice.
The reason for this is that ions are attracted to their opposites, and so negative ions surround positive ones and vice versa. You can think of this arrangement as a way to maximize the attractive forces between the cations and anions while minimizing the repulsive forces.
Another characteristic of this arrangement is how the sizes of the ions generally fit well together. When metals ionize, they lose an electron, making them decrease in size. When nonmetals ionize, they gain an electron, making them increase in size. You could see this periodic trend above with a sodium and chlorine atom ionizing. This allows the small cations (Na+ ions) to fit between the larger anions (Cl- ions). This does not happen for all ionic solids, but it is something to note as it impacts the forces experienced.
It is important to note that particle diagrams for ionic substances look different from that of molecular substances (that have covalent bonds). Covalent substances are usually represented by a molecule (such as H2O) while ionic substances are represented by a network of positive😊 and negative😞 ions.
The lattice structure can be explained by the strong electrostatic forces that arise between cations and anions because of their opposing charges. Coulomb's law describes these exact forces, telling us that the electrostatic force between a cation and an anion is directly proportional to their charges and inversely proportional to the distance between them.
It is rather important to understand that the strength of these electrostatic forces depends on two factors:
** Remember, attractive forces between cations and anions are maximized in the lattice structure while repulsive forces are minimized. **
Ionic substances are typically solids at room temperature and are known for their very high melting and boiling points. Let's break down the general properties of ionic substances:
Lattice Energy is the energy released when ions bond to form an ionic solid. We're back to Coulomb's law! It actually relates to lattice energy too; it's kind of everywhere.
Let's ease into lattice energy...do you also remember how to find out which ionic compound would have a higher melting point? Let's review that, it'll help with lattice energy I promise!
Lattice energy depends on the same two concepts that you used in that question: charge and distance. Coulomb's Law directly relates to melting point and lattice energy so just remember:
The smaller the size and the higher the charge, the higher the lattice energy🤔. Therefore, the higher the melting point of an ionic solid, the higher the lattice energy.
Easy rule, right? Let's try a few out:
Which of the following compounds has a higher lattice energy?
The following question is from the Advanced Placement YT Channel. All credit to them.
Answer the following questions related to Mg and Sr.
(1) Looking at the periodic table and remembering electron configuration, you should get:
You cannot leave the electron configurations of Mg and Sr as your final answer! Make sure you always answer what they are asking.
I originally wrote down the electron configurations of Mg and Sr and then took off two valence electrons to get the final electron configurations of cations Mg+2 and Sr+2.
(2) This question goes back to periodic trends. Which ion has more electrons and electron shells? Sr2+ does, so it has a larger ionic radius.
Sample Response: Sr+2 has a larger ionic radius than Mg+2 because it has more occupied electron shells. The valence electrons in Sr2+ are in the 4th energy level whereas the valence electrons in Mg2+ are in the 2nd energy level. Electrons in the 4th energy level are generally farther away from the nucleus, making the ion larger.
(3) Charges are the same, so size must be accountable for the difference in lattice energy.
Sample Response: Coulomb's law states that the higher the charges of the ions and the smaller the distance between the ions, the stronger the attraction and the higher the lattice energy. Although the charges of Mg+2 and Sr+2 are the same, Sr is a much larger ion due to its greater amount of occupied energy shells. Since it is larger, the distance between Sr+2 and the chlorine ions is greater than the distance between Mg+2 and the chlorine ions. Therefore, the lattice energy of SrCl2 (s) must be less than 2300 kJ/mol.
An anion is an atom or group of atoms that has gained one or more electrons, giving it a negative charge.
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An anion is an atom or group of atoms that has gained one or more electrons, giving it a negative charge.
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An ionic solid is a type of crystalline solid composed of ions. These are held together by ionic bonds, which are formed due to the electrostatic attraction between oppositely charged ions.
Cation: A cation is a positively charged ion that has lost one or more electrons.
Anion: An anion is a negatively charged ion that has gained one or more electrons.
Ionic Bond: This is the force of attraction between oppositely charged ions in an ionic compound. It's like the roads connecting our city buildings together!
A cation is an atom or group of atoms that has lost one or more electrons, giving it a positive charge.
Ionization Energy: The amount of energy required to remove an electron from an atom or ion. It’s like how much persuasion it would take for you to leave that party early!
Metallic Bonding: Metals often lose electrons easily, forming cations which then bond together through their shared sea of electrons. It's like a group of friends (the metal atoms) all deciding to leave the party early (lose electrons) and hang out together instead.
Electrolyte: A substance that produces an electrically conducting solution when dissolved in water. Cations are often part of electrolytes, like how you might be a key player in starting a new trend at school.
An anion is an atom or group of atoms that has gained one or more electrons, giving it a negative charge.
Electron Affinity: The amount of energy released when an electron is added to a neutral atom. It’s like how happy you would feel if someone gave you free pizza at the party!
Covalent Bonding: This type of bonding happens when two atoms share electrons. In some cases, one atom pulls on the shared electron(s) harder and becomes slightly negative, acting as an anion. It's like sharing your pizza with someone else but still holding onto most of it yourself.
Salt Bridge: In electrochemistry, this is a laboratory device used to connect the oxidation and reduction half-cells of a galvanic cell (a type of battery), allowing ion flow without extensive mixing of different solutions. Anions move towards the positive electrode through this bridge – think about it as if they’re drawn towards their favorite band playing on stage!
Ionic bonding is a type of chemical bond where one atom transfers one or more electrons to another atom, resulting in positive and negative ions which attract each other.
Covalent Bonding: A type of chemical bond where atoms share electron pairs with each other instead of transferring them.
Metallic Bonding: A type of chemical bond found in metals where electrons are shared among many atoms leading to properties such as conductivity and malleability.
Valence Electrons: These are electrons located in an atom's outermost shell. They participate in forming bonds with other atoms.
Valence electrons are the outermost electrons in an atom's electron configuration and have the potential to interact with other atoms. They play a key role in chemical reactions and bonding.
Electron Configuration: This refers to the distribution of electrons of an atom or molecule in atomic or molecular orbitals.
Covalent Bonding: This type of bonding happens when pairs of valence electrons are shared by atoms.
Ionization Energy: The energy required to remove one electron from an atom.
Coulomb's Law describes the force between two charged objects. It states that this force is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.
Electric Charge: This is a fundamental property of matter that can be either positive or negative, with like charges repelling and opposite charges attracting each other.
Inverse Square Law: This law states that a specified physical quantity or intensity is inversely proportional to the square of the distance from the source of that physical quantity.
Force Field: A region around a charged particle within which a force would be exerted on other charged particles or objects.
A crystal lattice is a symmetrical, three-dimensional arrangement of atoms or ions in a crystal. It's the repeating pattern of particles that forms the solid structure of a crystal.
Lattice Energy: This is the energy required to break apart an ionic compound and convert its component atoms into gaseous ions. It's like how much effort it would take to dismantle your LEGO structure into individual bricks.
Unit Cell: This is the smallest repeating unit in a crystal lattice that shows the entire pattern of atoms. It's like identifying one small section of your LEGO structure that, if repeated, could recreate the whole thing.
Ionic Bonding: This refers to when positively charged ions (cations) and negatively charged ions (anions) are attracted to each other and form bonds. Like magnets with opposite poles attracting each other.
Particle diagrams are visual representations used in chemistry to illustrate the arrangement and interactions of particles in a substance.
Molecular Structure: The three-dimensional arrangement of atoms within a molecule.
Atomic Structure: The arrangement of protons, neutrons, and electrons within an atom.
Phase Diagrams: Graphical representations showing how phases (states) of matter can change under varying conditions of temperature and pressure.
A lattice structure refers to an orderly arrangement of atoms, ions or molecules in a crystalline material or solid.
Crystal Lattice: The symmetrical three-dimensional arrangement of atoms inside a crystal.
Unit Cell: The smallest repeating unit in a crystal lattice, which reflects the entire structure of the crystal.
Ionic Lattice: A type of lattice structure where ions are arranged in a repeating pattern.
Electrostatic forces are the attractive or repulsive forces between particles that are caused by their electric charges.
Coulomb's Law: This law describes the force between two charged objects. It states that the force is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.
Electric Field: An area around a charged particle where an electric force is exerted on other charged particles.
Ionic Bonding: A type of chemical bonding that involves the electrostatic attraction between oppositely charged ions.
Materials that allow electric charges to flow through them easily.
Resistivity: The measure of a material's ability to oppose the flow of electric current.
Insulator: A material that does not allow electric charges to move freely, acting as a roadblock on our 'electricity highway'.
Semiconductor: A material whose conductivity falls between that of conductors and insulators. It's like a smaller road or street in our 'electricity highway' analogy.
This is the energy required to break apart an ionic compound and convert its component atoms into gaseous ions.
Ionic Compound: These are compounds composed of ions, charged particles that form when an atom gains or loses electrons. In our analogy, these are the individual lego blocks.
Ionization Energy: This is the energy required to remove an electron from a neutral atom. It's like trying to take a tiny piece off one of your lego blocks.
Electron Affinity: This is the amount of energy released when an electron is added to a neutral atom. It's like if adding another small piece onto your lego block made it suddenly become more stable and release energy.
The melting point is the temperature at which a solid will turn into a liquid under standard atmospheric conditions.
Freezing Point: This is the temperature at which a liquid turns into solid under standard pressure conditions.
Phase Transition: A change from one state of matter (solid, liquid, gas) to another without changing its chemical composition.
Heat Capacity: The measurable physical quantity that shows the amount of heat energy required to change an object's temperature by a given amount.
Periodic trends are specific patterns that are present in the periodic table that illustrate different aspects of a certain element, including its size and how it bonds with other elements.
Atomic Radius: This is half the distance between two nuclei of two identical atoms bonded together. It's like measuring the width of a building to understand its size.
Ionization Energy: This is the energy required to remove an electron from an atom or ion. Imagine if each floor of a building represented an electron - ionization energy would be like the effort needed to remove one floor from our building.
Electronegativity: This is a measure of how strongly atoms attract bonding electrons to themselves. In our city analogy, this could be compared to how attractive or popular certain neighborhoods are - some areas (atoms) draw more people (electrons) than others!