Question

Predict the empirical formulas of the ionic compounds formed from the following pairs of elements. Name each compound. a. \(\mathrm{Al}\) and \(\mathrm{Cl}\) c. \(\mathrm{Sr}\) and \(\mathrm{F}\) b. \(\mathrm{Na}\) and \(\mathrm{O}\) d. Ca and Se

Short answer

The empirical formulas and names of the ionic compounds formed from the given pairs of elements are: a. Aluminum and Chlorine: AlCl3, called "aluminum chloride." b. Sodium and Oxygen: Na2O, called "sodium oxide." c. Strontium and Fluorine: SrF2, called "strontium fluoride." d. Calcium and Selenium: CaSe, called "calcium selenide."

Step-by-step solution

a. Al and Cl

1. Determine the charges: Based on the periodic table, Al (aluminum) is a Group 3 element and commonly forms a 3+ ion, while Cl (chlorine) is a Group 7 element and commonly forms a 1- ion. 2. Combine to form a neutral compound: To balance the charges, we will need 3 Cl- ions to balance the 3+ charge on the Al ion. Thus, the empirical formula for the aluminum chloride compound will be AlCl3. 3. Name the compound: The compound formed from aluminum and chlorine is named "aluminum chloride."

b. Na and O

1. Determine the charges: Based on the periodic table, Na (sodium) is a Group 1 element and commonly forms a 1+ ion, while O (oxygen) is a Group 6 element and commonly forms a 2- ion. 2. Combine to form a neutral compound: To balance the charges, we will need 2 Na+ ions to balance the 2- charge on the O ion. Thus, the empirical formula for the sodium oxide compound will be Na2O. 3. Name the compound: The compound formed from sodium and oxygen is named "sodium oxide."

c. Sr and F

1. Determine the charges: Based on the periodic table, Sr (strontium) is a Group 2 element and commonly forms a 2+ ion, while F (fluorine) is a Group 7 element and commonly forms a 1- ion. 2. Combine to form a neutral compound: To balance the charges, we will need 2 F- ions to balance the 2+ charge on the Sr ion. Thus, the empirical formula for the strontium fluoride compound will be SrF2. 3. Name the compound: The compound formed from strontium and fluorine is named "strontium fluoride."

d. Ca and Se

1. Determine the charges: Based on the periodic table, Ca (calcium) is a Group 2 element and commonly forms a 2+ ion, while Se (selenium) is a Group 6 element and commonly forms a 2- ion. 2. Combine to form a neutral compound: The charges on Ca and Se ions are equal and opposite. We just need one ion of each to balance the charges. Thus, the empirical formula for the calcium selenide compound will be CaSe. 3. Name the compound: The compound formed from calcium and selenium is named "calcium selenide."

Key concepts

Ionic Compounds

Ionic compounds are formed when metals transfer electrons to nonmetals, creating charged particles called ions. Metals typically lose electrons and become positively charged, while nonmetals gain those electrons and become negatively charged. This transfer leads to the formation of a stable, neutral compound.

For instance:

• Aluminum (Al) loses 3 electrons to form a 3+ ion.
• Chlorine (Cl) gains 1 electron to form a 1- ion.

Combining these elements, three chloride ions are needed to balance the charge of one aluminum ion, resulting in the compound aluminum chloride (AlCl₃).
Ionic compounds often form crystalline solids with high melting points due to the strong electrostatic forces between the ions.

Chemical Naming

Naming ionic compounds follows a simple method based on the elements involved. The metal (cation) name is stated first, followed by the nonmetal (anion) with its ending changed to '-ide'. This systematic approach helps in clearly identifying compounds.

Examples include:

• AlCl₃ is named aluminum chloride, combining aluminum and chlorine.
• Na₂O is called sodium oxide, reflecting sodium combined with oxygen.

This naming convention is consistent across most simple ionic compounds, providing a straightforward way of understanding their composition.

Periodic Table

The periodic table is a powerful tool in predicting how elements will interact to form compounds. Elements are grouped based on their properties, with predictable patterns of behavior.

For ionic compounds:

• Group 1 elements, like sodium (Na), form 1+ ions.
• Group 2 elements, such as calcium (Ca), form 2+ ions.
• Nonmetals in Group 6, like oxygen (O), form 2- ions.
• Group 7 elements, including fluorine (F) and chlorine (Cl), form 1- ions.

These trends help determine the ratio of ions needed to form neutral compounds, making predictions about empirical formulas clearer.

Charge Balance

For an ionic compound to be stable, the total positive charges must balance the total negative charges, resulting in no overall charge. This principle of charge balance ensures stability.

Consider these examples:

• In SrF₂, strontium (Sr) forms a 2+ ion, requiring two 1- fluoride ions to balance it.
• CaSe shows calcium (Ca) and selenium (Se) both forming 2+ and 2- ions respectively, naturally balancing each other.

Understanding charge balance helps predict the necessary ratio of ions and is fundamental in writing correct empirical formulas for ionic compounds.