Problem 14 - Chemistry: The Central Science in SI Units, Global Edition

Question

Consider the elements \(\mathrm{Ba}, \mathrm{Na}, \mathrm{O}, \mathrm{B}, \mathrm{P},\) and \(\mathrm{Kr}\). From this list, select the element that (a) is most electronegative, (b) has the greatest metallic character, \((\mathbf{c})\) most readily forms a positive ion, \((\mathbf{d})\) exhibits a maximum oxidation sate of +5 , (e) exists as monoatomic gas at room temperature, (f) has multiple allotropes.

Step-by-Step Solution

Answer

\(a)\) Oxygen (O) is the most electronegative element. \(b)\) Barium (Ba) has the greatest metallic character. \(c)\) Sodium (Na) most readily forms a positive ion. \(d)\) Phosphorus (P) exhibits a maximum oxidation state of +5. \(e)\) Krypton (Kr) exists as a monoatomic gas at room temperature. \(f)\) Both boron (B) and phosphorus (P) have multiple allotropes.

Step 1: Find the element with the highest electronegativity

We can use the periodic table to identify the element with the highest electronegativity. Generally, electronegativity increases from left to right across a period and decreases down a group. Among the given elements, O (oxygen) is in Group 16 (chalcogens) and Period 2, which is the most right and up in the periodic table, so it is the most electronegative element in the list. #b) Element with the greatest metallic character#

Step 2: Find the element with the greatest metallic character

Metallic character decreases across a period and increases down a group in the periodic table. Ba (barium) is in Group 2 (alkaline earth metals) and Period 6, which is the most left and down in the periodic table, so it has the greatest metallic character among the given elements. #c) Element that most readily forms a positive ion#

Step 3: Find the element that most readily forms a positive ion

Elements that easily form positive ions usually have low ionization energies. Metallic elements generally have lower ionization energies than nonmetals. Among the given elements, Na (sodium) is an alkali metal (Group 1) and will lose one electron easily to form a positive ion (Na+). So, Na most readily forms a positive ion. #d) Element that exhibits a maximum oxidation state of +5#

Step 4: Find the element with a maximum oxidation state of +5

Elements in Group 15 tend to have a maximum oxidation state of +5 due to the presence of 5 valence electrons. In our given list, P (phosphorus) is in Group 15, and thus it exhibits a maximum oxidation state of +5. #e) Element that exists as monoatomic gas at room temperature#

Step 5: Find the monoatomic gas element at room temperature

Noble gases are the only elements that exist as monoatomic gases at room temperature due to their stable electron configurations and are placed in Group 18 of the periodic table. In our given list, Kr (krypton) is a noble gas and exists as a monoatomic gas at room temperature. #f) Element with multiple allotropes#

Step 6: Find the element with multiple allotropes

Allotropy is a phenomenon in which an element can exist in two or more different forms with different physical and sometimes chemical properties. B (boron) and P (phosphorus) are both known to have several allotropes. For example, B has two main allotropes: α-boron and β-boron, and P has multiple allotropes, including white, red, and black phosphorus.

Key Concepts

Electronegativity

Electronegativity is a term you might encounter often in chemistry. It describes an element's ability to attract and hold onto electrons. As you move across a period in the periodic table from left to right, electronegativity tends to increase. This is because the atoms become smaller and the positive charge of the nucleus can attract the electrons more strongly. Conversely, as you move down a group, electronegativity decreases because the atoms become larger, and the outer electrons are further from the nucleus.
Among the elements listed, oxygen (\(O\)) is known for having the highest electronegativity. It is positioned on the very top right of the periodic table (except for the noble gases which have full outer electron shells), making it highly effective at attracting electrons during chemical reactions. Understanding electronegativity helps predict how elements will interact in chemical compounds.

Metallic Character

When we talk about metallic character, we're discussing how closely an element's properties align with those of metals. Metals are characterized by their tendency to lose electrons, conduct electricity, and have a shiny luster. The metallic character of elements decreases as you move across a period from left to right and increases as you move down a group in the periodic table.
From the provided list, barium (\(Ba\)) exhibits the greatest metallic character. It is located on the bottom left side of the periodic table among the alkaline earth metals. This position signifies a strong tendency to lose electrons and hence, a pronounced metallic character. Knowing which elements exhibit metallic properties can be useful, especially when predicting the types of bonds they might form.

Oxidation States

Oxidation states are numbers that indicate the degree of oxidation or reduction of an element in a chemical compound. Essentially, it reflects the number of electrons lost or gained by an atom to form that compound. Elements in Group 15, such as phosphorus (\(P\)), can exhibit an oxidation state of +5 because they have five valence electrons.
Phosphorus is versatile, capable of participating in a range of chemical reactions due to its ability to attain this +5 oxidation state. Understanding oxidation states is crucial for balancing chemical equations and predicting reaction products.

Monoatomic Gases

Monoatomic gases are gases that consist of single atoms. The noble gases, located in Group 18 of the periodic table, are naturally found as monoatomic gases due to their stable electron configurations. Their outer electron shells are complete, making them largely non-reactive with other elements.
Krypton (\(Kr\)) is one such monoatomic gas. It is inert and exists naturally as standalone atoms at room temperature. Recognizing which gases are monoatomic is important in fields like chemistry and physics, as it can influence the behavior of gases under different conditions.

Allotropes

Allotropes are different forms of the same element, where the atoms are bonded together in different ways. This can result in varying physical and chemical properties despite being composed of the same type of atoms. For example, phosphorus (\(P\)) exhibits multiple allotropes, such as white, red, and black phosphorus, each with unique characteristics and uses.
Boron (\(B\)) is another element that has several allotropes, including α-boron and β-boron. These exist due to the different spatial arrangements of atoms in the solid state. Allotropy is a fascinating concept because it demonstrates how atomic arrangement can significantly affect an element's properties.