Chapter 3: Problem 48
Predict the empirical formulas of the ionic compounds formed from the following pairs of elements. Name each compound. a. Al and Cl b. Na and O c. Sr and F d. Ca and Se
Short Answer
Expert verified
a. AlCl₃ - Aluminium chloride
b. Na₂O - Sodium oxide
c. SrF₂ - Strontium fluoride
d. CaSe - Calcium selenide
Step by step solution
01
a. Al and Cl
1. Determine the charges of the ions:
Aluminium (Al) forms a +3 ion, while chlorine (Cl) forms a -1 ion.
2. Balance the charges:
To obtain a neutral compound, we require 3 Cl ions for each Al ion. This gives us the empirical formula:
AlCl₃
3. Name the compound:
The compound is named using the names of the two ions: Aluminium chloride.
02
b. Na and O
1. Determine the charges of the ions:
Sodium (Na) forms a +1 ion, while oxygen (O) forms a -2 ion.
2. Balance the charges:
To obtain a neutral compound, we require 2 Na ions for each O ion. This gives us the empirical formula:
Na₂O
3. Name the compound:
The compound is named using the names of the two ions: Sodium oxide.
03
c. Sr and F
1. Determine the charges of the ions:
Strontium (Sr) forms a +2 ion, while fluorine (F) forms a -1 ion.
2. Balance the charges:
To obtain a neutral compound, we require 2 F ions for each Sr ion. This gives us the empirical formula:
SrF₂
3. Name the compound:
The compound is named using the names of the two ions: Strontium fluoride.
04
d. Ca and Se
1. Determine the charges of the ions:
Calcium (Ca) forms a +2 ion, while selenium (Se) forms a -2 ion.
2. Balance the charges:
To obtain a neutral compound, one Ca ion combines with one Se ion. This gives us the empirical formula:
CaSe
3. Name the compound:
The compound is named using the names of the two ions: Calcium selenide.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Empirical Formula
The empirical formula of an ionic compound represents the simplest whole-number ratio of each type of ion in the compound. For example, when forming a compound from aluminum and chlorine, we get the formula \( \text{AlCl}_3 \). This shows that for every one aluminum ion, three chloride ions are present.
To arrive at this simplest ratio, consider the charges of the ions involved, as ions combine to form a neutral compound. If one element's ion has a different charge magnitude, you need multiples to achieve a zero net charge.
This concept is central to determining the composition of compounds, ensuring the compound's overall charge is neutral. Using the empirical formula, you can also deduce relative quantities of each ion in diverse chemical reactions.
To arrive at this simplest ratio, consider the charges of the ions involved, as ions combine to form a neutral compound. If one element's ion has a different charge magnitude, you need multiples to achieve a zero net charge.
This concept is central to determining the composition of compounds, ensuring the compound's overall charge is neutral. Using the empirical formula, you can also deduce relative quantities of each ion in diverse chemical reactions.
Ion Charges
Ionic compounds are made of positive and negative ions. Each ion carries a specific charge, and this charge determines how they combine.
For instance, aluminum forms a +3 ion (\( \text{Al}^{3+} \)) while chlorine forms a -1 ion (\( \text{Cl}^- \)). These charges arise from atoms either losing or gaining electrons to achieve a stable electron arrangement.
Understanding these charges is vital because the total charge of the compound must be zero. For example, in the compound \( \text{SrF}_2 \), strontium (\( \text{Sr}^{2+} \)) combines with two fluoride ions (\( \text{F}^- \)) to balance the charges and ensure neutrality.
For instance, aluminum forms a +3 ion (\( \text{Al}^{3+} \)) while chlorine forms a -1 ion (\( \text{Cl}^- \)). These charges arise from atoms either losing or gaining electrons to achieve a stable electron arrangement.
Understanding these charges is vital because the total charge of the compound must be zero. For example, in the compound \( \text{SrF}_2 \), strontium (\( \text{Sr}^{2+} \)) combines with two fluoride ions (\( \text{F}^- \)) to balance the charges and ensure neutrality.
- Positive ions (cations) form when atoms lose electrons.
- Negative ions (anions) form when atoms gain electrons.
Naming Compounds
Naming ionic compounds involves combining the names of the metal (positive ion) and the non-metal (negative ion).
For example, in \( \text{Na}_2\text{O} \), the compound is named sodium oxide. Here, 'sodium' refers to the metal ion and 'oxide' is derived from oxygen, the non-metal ion.
The naming convention initially states the name of the metal ion first, followed by the non-metal with its ending replaced by 'ide', such as chloride, oxide, or selenide.
This systematic method helps convey both the component ions and the proportions in which they appear, ensuring clear communication in chemical discussions.
For example, in \( \text{Na}_2\text{O} \), the compound is named sodium oxide. Here, 'sodium' refers to the metal ion and 'oxide' is derived from oxygen, the non-metal ion.
The naming convention initially states the name of the metal ion first, followed by the non-metal with its ending replaced by 'ide', such as chloride, oxide, or selenide.
This systematic method helps convey both the component ions and the proportions in which they appear, ensuring clear communication in chemical discussions.
Neutral Compound Balance
Achieving a neutral compound balance in ionic compounds ensures the total positive charge equals the total negative charge. This equilibrium is vital in formulating the empirical formula of ionic compounds.
Consider the compound formed by mixing calcium and selenium: \( \text{CaSe} \). Here, calcium is a +2 ion (\( \text{Ca}^{2+} \)) and selenium is a -2 ion (\( \text{Se}^{2-} \)), thus one ion of each forms a neutral compound.
Importantly, balance requires considering the charge of each participating ion. In \( \text{Na}_2\text{O} \), two sodium ions, each with a +1 charge, balance one oxide ion's -2 charge.
Consider the compound formed by mixing calcium and selenium: \( \text{CaSe} \). Here, calcium is a +2 ion (\( \text{Ca}^{2+} \)) and selenium is a -2 ion (\( \text{Se}^{2-} \)), thus one ion of each forms a neutral compound.
Importantly, balance requires considering the charge of each participating ion. In \( \text{Na}_2\text{O} \), two sodium ions, each with a +1 charge, balance one oxide ion's -2 charge.
- Start by identifying the charge of each ion.
- Next, find the least common multiple of their charges to determine the smallest whole number of each ion.