Question

Which compounds are not likely to occur: \(\mathrm{CaKr}, \mathrm{Na}_{2} \mathrm{S}\) \(\mathrm{BaCl}_{3}, \mathrm{MgF} ?\) Explain your choices.

Short answer

The compounds CaKr, \(\mathrm{BaCl}_3\), and MgF are not likely to occur because noble gases, such as Krypton (Kr), rarely bond with other elements and the charges in \(\mathrm{BaCl}_3\) and MgF are unbalanced. The compound \(\mathrm{Na}_2\mathrm{S}\) is likely to occur since it follows the rules for ionic compound formation, with balanced charges between Sodium (Na) and Sulfur (S).

Step-by-step solution

Identify the Types of Elements

Look at each compound and determine if each element in the compound is a metal, non-metal, or noble gas. - Calcium (Ca) is an alkaline earth metal, while Krypton (Kr) is a noble gas. - Sodium (Na) is an alkali metal, and Sulfur (S) is a non-metal. - Barium (Ba) is an alkaline earth metal, and Chlorine (Cl) is a halogen (non-metal). - Magnesium (Mg) is an alkaline earth metal, and Fluorine (F) is a halogen (non-metal). Notice that CaKr has a noble gas, while the others are composed of one metal element and one non-metal element.

Examine the Charges and Formation of Ionic Compounds

Evaluate whether the charges of the elements bond correctly in an ionic compound formation. 1. CaKr: Noble gases inherently have a full valence electron shell and thus are unlikely to bond with other elements. Therefore, CaKr is not likely to occur. 2. \(\mathrm{Na}_2\mathrm{S}\): Sodium has a charge of +1, and Sulfur has a charge of -2. To balance the charges, we need two Sodium ions for every Sulfur ion. Thus, \(\mathrm{Na}_2\mathrm{S}\) is a balanced ionic compound and is likely to occur. 3. BaCl\(_3\): Barium has a charge of +2, and Chlorine has a charge of -1. To balance the charges in this compound, we would need one Barium ion and two Chloride ions. So the compound \(\mathrm{BaCl}_2\) would be correct, but \(\mathrm{BaCl}_3\) is not likely to occur due to an unbalanced charge. 4. MgF: Magnesium has a charge of +2, and Fluorine has a charge of -1. Following similar logic as before, the balanced ionic compound would be \(\mathrm{MgF}_2\). Therefore, the compound MgF is not likely to occur. Based on examining the types of elements and their charges, we can conclude that the compounds CaKr, \(\mathrm{BaCl}_3\) and MgF are not likely to occur due to either the presence of a noble gas or incorrect balancing of charges. The compound \(\mathrm{Na}_2\mathrm{S}\) is likely to occur because it follows the rules for ionic compound formation.

Key concepts

Chemical Bond Types

Understanding the different types of chemical bonds is crucial for explaining why certain compounds are less likely to form than others. In essence, chemical bonds are the attractive forces that hold atoms together in a compound. There are three primary types of chemical bonds: ionic, covalent, and metallic.

Ionic bonds occur between metals and non-metals. Metals tend to lose electrons and become positively charged ions, known as cations, while non-metals tend to gain electrons and become negatively charged ions, known as anions. The electrostatic attraction between these oppositely charged ions forms an ionic bond.

Covalent bonds, on the other hand, involve the sharing of valence electrons between two non-metals. Unlike ionic bonds, there is no transfer of electrons but rather a mutual sharing to achieve a full valence shell.

Metallic bonds are found in solid metals and alloys where electrons are free to move within a 'sea' of delocalized electrons around positive metal ions. This unique bonding leads to properties like conductivity and malleability.

Knowing the nature of these bonds helps to explain why a compound like CaKr would not likely form. Noble gases, such as Krypton, are unique in that they typically do not form chemical bonds due to having a full valence electron shell, making the proposed CaKr compound improbable.

Valence Electrons

Valence electrons are the electrons that reside in the outermost shell of an atom and are crucial in determining how an atom will chemically react. These electrons are responsible for the formation of chemical bonds as they are lost, gained, or shared between atoms during reactions.

An atom is most stable when its outer shell is complete. For most elements, a full outer shell means having eight valence electrons, which is known as the octet rule. Elements will either lose, gain, or share electrons to reach this state of stability.

Metals, such as Sodium (Na) and Magnesium (Mg), which are involved in our exercise, have one to three valence electrons that they can readily lose to achieve a full shell. Conversely, non-metals like Sulfur (S) and Fluorine (F) are close to having a full valence shell and tend to gain electrons to satisfy the octet rule.

When analyzing potential compounds, the number of valence electrons and the ability for elements to reach stable electron configurations are key. For example, Sodium (Na) can lose one electron to form Na+, and Sulfur (S) can gain two electrons to form S2-, leading to the formation of a stable compound, Na₂S. This illustrates the importance of valence electrons in predicting compound formation.

Ionic Charges

Ionic charges play a pivotal role in the formation of ionic compounds. An ionic charge is the electric charge an atom acquires when it gains or loses electrons to achieve a stable electron configuration.

When elements form ionic compounds, they tend to achieve noble gas electron configurations. Metals, with fewer valence electrons, will typically lose these electrons and become positively charged. Alternatively, non-metals, which need additional electrons to complete their valence shell, will gain electrons and become negatively charged. The resulting ions have opposite charges, and this difference in charge is what drives the formation of ionic bonds.

For stable ionic compound formation, the total positive charge must balance the total negative charge. As the exercise suggests, a compound like BaCl₃ is improbable because the charges do not balance. Barium (Ba) has a charge of +2, while Chlorine (Cl) has a charge of -1. The appropriate compound that exhibits a balance of charges would be BaCl₂, where one Ba²⁺ ion pairs with two Cl^- ions. This balance is what ultimately dictates which ionic compounds are likely to form and which are not.