Ch.2 - Atoms, Molecules, and Ions

Brown - Chemistry: The Central Science 14th Edition

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Brown 14th Edition

Ch.2 - Atoms, Molecules, and Ions

Problem 60b

Chapter 2, Problem 60b

The most common charge associated with selenium is 2-. Indicate the chemical formulas you would expect for compounds formed between selenium and (b) lithium

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Identify the charge of selenium: Selenium typically forms a 2- charge, denoted as Se^{2-}.

Identify the charge of lithium: Lithium is an alkali metal and typically forms a 1+ charge, denoted as Li^{+}.

Determine the ratio of lithium ions to selenium ions needed to balance the charges: Since selenium has a 2- charge and lithium has a 1+ charge, you will need two lithium ions to balance one selenium ion.

Write the chemical formula by combining the ions in the correct ratio: The formula will be Li_2Se, indicating two lithium ions for every one selenium ion.

Verify the charge balance: Ensure that the total positive charge from lithium (2 x 1+) equals the total negative charge from selenium (1 x 2-), confirming the compound is neutral.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Ionic Bonding

Ionic bonding occurs when atoms transfer electrons to achieve full outer electron shells, resulting in the formation of charged ions. In this case, lithium, which has a tendency to lose one electron and form a Li+ ion, will bond with selenium, which typically gains two electrons to form a Se2- ion. The resulting compound will be electrically neutral, balancing the charges of the ions.

Chemical Formula Representation

A chemical formula represents the types and numbers of atoms in a compound. For ionic compounds, the formula is derived from the ratio of the ions that balance the overall charge. In the case of lithium and selenium, the formula must reflect the 2:1 ratio of lithium ions to selenium ions to ensure charge neutrality, leading to the formula Li2Se.

Charge Balance in Compounds

Charge balance is a fundamental principle in chemistry that states that the total positive charge must equal the total negative charge in a neutral compound. For lithium (Li+) and selenium (Se2-), two lithium ions are needed to balance the charge of one selenium ion, resulting in a neutral compound. This principle is crucial for determining the correct stoichiometry in ionic compounds.

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