Chemistry: Ionic Bonding and Lattice Structures
Electron transfer, crystal lattices, and properties of ionic compounds
Chemistry: Ionic Bonding and Lattice Structures
Electron transfer, crystal lattices, and properties of ionic compounds
Chemistry - Grade 9-12
- 1
Explain how an ionic bond forms between sodium and chlorine atoms. Include what happens to the electrons and name the ions that form.
Sodium is in Group 1 and chlorine is in Group 17.
Sodium transfers one valence electron to chlorine. Sodium becomes a sodium ion, Na+, and chlorine becomes a chloride ion, Cl-. The attraction between the oppositely charged ions forms an ionic bond. - 2
Write the correct chemical formula for the ionic compound formed from magnesium ions, Mg2+, and oxide ions, O2-. Explain why this formula is neutral.
The formula is MgO. One Mg2+ ion and one O2- ion have charges that add to zero, so the compound is electrically neutral. - 3
Write the correct chemical formula for the ionic compound formed from aluminum ions, Al3+, and chloride ions, Cl-. Explain how you balanced the charges.
The total positive charge must equal the total negative charge.
The formula is AlCl3. One Al3+ ion needs three Cl- ions so the total charge is 3+ plus 3-, which equals zero. - 4
A compound has the formula CaF2. Identify the ions present and state the charge on each ion.
The compound contains calcium ions, Ca2+, and fluoride ions, F-. Two fluoride ions are needed for each calcium ion to balance the 2+ charge. - 5
Draw or describe the Lewis dot process for forming lithium fluoride, LiF. State which atom loses an electron and which atom gains an electron.
Lithium needs to lose one electron, while fluorine needs one electron to complete its octet.
Lithium has one valence electron and loses it to become Li+. Fluorine has seven valence electrons and gains one electron to become F-. The resulting ions attract to form LiF. - 6
Explain why solid sodium chloride does not conduct electricity, but molten sodium chloride does conduct electricity.
Electric current in ionic substances requires moving charged particles.
Solid sodium chloride does not conduct electricity because its ions are locked in fixed positions in the crystal lattice. Molten sodium chloride conducts electricity because the ions can move and carry electric charge. - 7
Compare the lattice energy of NaCl and MgO. Which compound would you expect to have the larger lattice energy, and why?
Lattice energy increases when ionic charges increase and when ion size decreases.
MgO would have the larger lattice energy because Mg2+ and O2- have greater charges than Na+ and Cl-. Stronger attractions between higher charged ions produce a larger lattice energy. - 8
Rank these ionic compounds from lowest to highest expected melting point: NaF, MgO, KBr. Explain your ranking using ion charge and ion size.
A reasonable ranking is KBr, NaF, MgO from lowest to highest melting point. KBr has larger singly charged ions, NaF has smaller singly charged ions with stronger attraction, and MgO has 2+ and 2- ions with the strongest attraction. - 9
In a sodium chloride crystal lattice, each Na+ ion is surrounded by 6 Cl- ions, and each Cl- ion is surrounded by 6 Na+ ions. What is the coordination number for each ion?
The coordination number for Na+ is 6, and the coordination number for Cl- is also 6. Coordination number is the number of nearest oppositely charged ions around an ion. - 10
Cesium chloride has a crystal structure in which each Cs+ ion is surrounded by 8 Cl- ions. How does this coordination number compare with sodium chloride, and what does it tell you about the lattice arrangement?
Coordination number describes the number of nearest neighbors with opposite charge.
Cesium chloride has a coordination number of 8, while sodium chloride has a coordination number of 6. This means the ions in cesium chloride are arranged so that each ion has more nearest opposite-charge neighbors. - 11
Explain why ionic compounds are usually brittle rather than flexible.
Ionic compounds are brittle because shifting layers in the crystal can bring ions with the same charge next to each other. The repulsion between like charges causes the crystal to crack or shatter. - 12
A student says, "Ionic compounds are made of molecules." Correct this statement using sodium chloride as an example.
Think about what a formula unit means.
Ionic compounds are not made of separate molecules. Sodium chloride exists as a repeating crystal lattice of Na+ and Cl- ions, and the formula NaCl gives the simplest whole-number ratio of ions. - 13
Write the formula and name of the compound formed from potassium ions and sulfate ions, SO4 2-. Explain how the charges are balanced.
The formula is K2SO4, and the compound is potassium sulfate. Two K+ ions are needed to balance the 2- charge on one sulfate ion. - 14
Use Coulomb's law ideas to explain why LiF generally has stronger ionic attractions than KI.
For ions with the same charges, smaller distance means stronger attraction.
LiF generally has stronger ionic attractions because Li+ and F- are smaller ions than K+ and I-. The smaller distance between ion centers produces a stronger attraction, even though both compounds contain ions with 1+ and 1- charges. - 15
A diagram shows alternating positive and negative ions arranged in a repeating pattern. Describe two features that identify the structure as an ionic lattice.
An ionic lattice has a repeating three-dimensional pattern of ions and contains alternating positive and negative ions. Each ion is attracted to nearby ions with the opposite charge, forming a strong crystal structure.