Problem 57 - Chemistry The Central Science In Si Units

Question

Write a molecular formula for each compound, and indicate the oxidation state of the group 15 element in each formula: (a) hexafluoroantimonate(V) ion, (b) calcium phosphate, (c) potassium dihydrogen phosphate, (d) arsenic trioxide, (e) tetraphosphorus hexaoxide, (f) arsenic trifluoride.

Step-by-Step Solution

Answer

(a) \([\text{SbF}_6]^−\), Sb +5; (b) \(\text{Ca}_3(\text{PO}_4)_2\), P +5; (c) \(\text{KH}_2\text{PO}_4\), P +5; (d) \(\text{As}_2\text{O}_3\), As +3; (e) \(\text{P}_4\text{O}_6\), P +3; (f) \(\text{AsF}_3\), As +3.

Step 1: Understanding the Molecular Formula for Hexafluoroantimonate(V) Ion

Identify the components: 'hexafluoro' refers to six fluorine atoms and 'antimonate(V)' refers to an antimony ion with an oxidation state of +5. The molecular formula is \( [\text{SbF}_6]^− \). The oxidation state of the antimony (Sb) is +5.

Step 2: Understanding the Molecular Formula for Calcium Phosphate

Calcium phosphate consists of calcium ions \( ext{Ca}^{2+} \) and the phosphate ion \( \text{PO}_4^{3-} \). The compound formula is \( \text{Ca}_3(\text{PO}_4)_2 \). The oxidation state of phosphorus in the phosphate ion is +5.

Step 3: Understanding the Molecular Formula for Potassium Dihydrogen Phosphate

Potassium dihydrogen phosphate involves potassium \( ext{K}^+ \), hydrogen phosphate \( \text{H}_2\text{PO}_4^- \). The formula is \( \text{KH}_2\text{PO}_4 \). The oxidation state of phosphorus (P) is +5.

Step 4: Understanding the Molecular Formula for Arsenic Trioxide

In arsenic trioxide, arsenic atoms are bonded with oxygen, with a formula \( \text{As}_2\text{O}_3 \). The oxidation state of arsenic (As) here is +3.

Step 5: Understanding the Molecular Formula for Tetraphosphorus Hexaoxide

Tetraphosphorus hexaoxide is essentially tetraphosphorus heptoxide with a missing oxygen atom: \( \text{P}_4\text{O}_6 \). The oxidation state of phosphorus in this compound is +3.

Step 6: Understanding the Molecular Formula for Arsenic Trifluoride

Arsenic trifluoride is composed of one arsenic and three fluorine atoms: \( \text{AsF}_3 \). The oxidation state of arsenic (As) in \( \text{AsF}_3 \) is +3.

Key Concepts

Oxidation States

Oxidation states, also known as oxidation numbers, are a crucial concept in chemistry that help us understand how electrons are distributed in compounds. They essentially indicate the degree of oxidation of an atom compared to its elemental state. Each element can exhibit multiple oxidation states, depending on the compound it is part of.

• Positive oxidation states arise when an element in a compound loses electrons (oxidation).
• Negative oxidation states occur when an element gains electrons (reduction).

For example, in the compound hexafluoroantimonate(V) ion, antimony (Sb) has an oxidation state of +5. This means it has lost five electrons compared to its neutral state. It is important to note that the sum of oxidation states in a compound must equal the overall charge of the compound. This principle helps us figure out the oxidation states of elements in compounds.

Group 15 Elements

The group 15 elements, also sometimes called the nitrogen family, include nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi). These elements are known for their ability to form stable compounds with different oxidation states, typically ranging from -3 to +5. This range allows them to create a variety of chemical compounds.

• Nitrogen: Common oxidation states of nitrogen include -3, in compounds like ammonia ( H_3) and +5, as seen in nitric acid ( HNO_3).
• Phosphorus: Phosphorus commonly shows oxidation states of -3, 0, +3, and +5. For example, in phosphorus pentoxide ( P_4O_10), phosphorus is in the +5 state.
• Arsenic: Arsenic is similarly versatile, as shown in compounds like arsenic trioxide ( As_2O_3) and arsenic trifluoride ( AsF_3), where arsenic has an oxidation state of +3.

These elements often form compounds with each other and with other elements, especially due to their ability to form covalent bonds.

Chemical Compounds

Chemical compounds are formed when two or more different elements combine in fixed proportions. These compounds can be categorized into molecular and ionic compounds.

• Molecular Compounds: Composed of molecules formed by atoms sharing electrons. An example is arsenic trifluoride ( AsF_3), where arsenic shares electrons with fluorine.
• Ionic Compounds: Created by transferring electrons from metal to non-metal atoms. Calcium phosphate ( Ca_3(PO_4)_2) is a good example, where calcium ions ( Ca^{2+}) combine with phosphate ions ( PO_4^{3-}).

The formulas of these compounds give vital information about the constituent elements and their quantities. For instance, the formula of tetraphosphorus hexaoxide ( P_4O_6) reveals that the compound consists of four phosphorus atoms bonded with six oxygen atoms.

Inorganic Chemistry

Inorganic chemistry is a branch that focuses on compounds that are not based on carbon-hydrogen (C-H) bonds, unlike organic chemistry. It covers a vast array of compounds, including salts, metals, minerals, and organometallic compounds.

• Inorganic compounds often contain elements from all parts of the periodic table, ranging from metals to non-metals and metalloids.
• They typically have high melting points and are usually not flammable.
• Inorganic chemistry is deeply rooted in studying how elements interact to form compounds like calcium phosphate or arsenic trioxide, which are crucial in various industrial applications.

While organic chemistry revolves more around carbon-based compounds, inorganic chemistry delves into understanding the diverse reactions and structures of compounds formed by elements like those in Group 15.