Question

Consider the elements L.i, K, Cl, C, Ne, and Ar. From this list, select the element that (a) is most clectronegative, (b) has the greatest metallic character, (c) most readily forms a positive ion, (d) has the smallest atomic radius, (c) forms \(\pi\) bonds most readily, (f) has multiple allotropes.

Short answer

In summary: (a) Most electronegative is Cl, (b) greatest metallic character is K, (c) most readily forms a positive ion is K, (d) smallest atomic radius is Ne, (e) forms π bonds most readily is C, and (f) has multiple allotropes is C.

Step-by-step solution

(a) Most Electronegative

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. Elements with higher electronegativity are found towards the upper right corner of the periodic table, excluding noble gases. Among the given elements, Cl is in the upper right corner and has the highest electronegativity. Therefore, the most electronegative element is Cl.

(b) Greatest Metallic Character

Metallic character refers to how easily an element can lose electrons, and it decreases across a period and increases down a group in the periodic table. Among the elements given, K is farthest to the left and down, indicating the greatest metallic character. Therefore, the element with the greatest metallic character is K.

(c) Most Readily Forms a Positive Ion

An element that readily forms positive ions does so by losing electrons. As discussed in part (b), K has the greatest metallic character and is most likely to lose electrons. Therefore, the element that most readily forms a positive ion is K.

(d) Smallest Atomic Radius

Atomic radius decreases across a period (from left to right) and increases down a group (from top to bottom) in the periodic table. Among the elements given, Ne is farthest to the right and closest to the top. Therefore, the element with the smallest atomic radius is Ne.

(e) Forms π Bonds Most Readily

π (pi) bonds are typically formed by the sideways overlap of p orbitals in atoms like carbon (C). Carbon is known for its ability to form π bonds, such as in carbon-carbon double and triple bonds, essential for organic chemistry. Therefore, the element that forms π bonds most readily is C.

(f) Has Multiple Allotropes

Allotropy is the property of some chemical elements to exist in two or more different forms, known as allotropes. Among the given elements, carbon is well-known for having multiple allotropes, such as diamond, graphite, and fullerenes. Therefore, the element with multiple allotropes is C.

Key concepts

Electronegativity

Electronegativity is a key concept in chemistry that describes how strongly an atom can attract a bonding pair of electrons. This property is crucial in determining how atoms will bond with each other. Generally, electronegativity increases across a period (from left to right) and decreases down a group (from top to bottom) on the periodic table.
Elements at the top right corner of the periodic table, like chlorine (Cl), fluorine (F), and oxygen (O), are highly electronegative, whereas metals to the bottom left are less electronegative. Noble gases are typically excluded from electronegativity trends because they do not readily form bonds. Among the elements given, chlorine (Cl) is the most electronegative.
This means it has a strong tendency to attract electrons during chemical interactions, making it a potent oxidizing agent and a key player in many reactions.

Metallic Character

Metallic character is essentially the set of attributes that define metals, such as their ability to conduct electricity and heat, as well as their tendency to lose electrons. The metallic character decreases as you move across a period and increases as you go down a group in the periodic table.
For instance, alkali metals, like potassium (K), exhibit strong metallic character because they easily lose their outermost electron to form positive ions, a feature crucial for their reactivity.
In comparison with the other elements listed, potassium stands out for having the greatest metallic character, making it very reactive and good at forming positive ions in chemical processes. This understanding helps us predict how a metal will behave in reactions, which is vital for applications in industries and for understanding natural processes.

Atomic Radius

The atomic radius is an important atomic property, representing the size of an atom. Essentially, it is the distance from the nucleus to the outermost shell of an electron cloud surrounding it.
As a general trend, the atomic radius decreases across a period due to increasing nuclear charge, which pulls electrons closer to the nucleus, and increases down a group as additional electron shells are added, expanding the size of the atom.
In the set of elements provided, neon (Ne) has the smallest atomic radius. Its small size is a result of strong nuclear attraction relative to its electron count, given it's located far right and near the top of the periodic table. Knowing atomic radii helps in predicting molecule shapes, bond strengths, and reactivity, which are crucial for understanding and designing chemical processes.

Allotropes

Allotropes are different structural forms in which an element can exist. This fascinating property occurs mainly in some nonmetals, allowing the same element to display different physical and chemical properties.
For example, carbon is famous for its allotropes such as diamond, graphite, and fullerenes. Each allotrope has distinct properties due to differences in the arrangement of carbon atoms.

• Diamond is extremely hard, transparent, and is an excellent insulator.
• Graphite has a slippery, layered structure that conducts electricity.
• Fullerenes have a spherical shape and interesting electronic and thermal properties.

These differences make the study of allotropes valuable for various applications, from industrial use to the development of new materials in nanotechnology.

Pi Bonds

Pi bonds (\( \pi \) bonds) are a type of covalent bond that is formed by the side-by-side overlap of p orbitals. This occurs in addition to a sigma bond to complete double or triple bonds between atoms, making them crucial for the structure of molecules like alkenes and alkynes.
Carbon is exceptional in its ability to form \( \pi \) bonds, particularly in organic compounds. This ability to form double and triple bonds contributes to the diversity and complexity of organic chemistry.
Unlike sigma bonds, \( \pi \) bonds are generally weaker and more reactive, allowing for a variety of chemical reactions that are fundamental to different chemical processes. Understanding \( \pi \) bonds is essential for designing molecules and predicting reactivity in organic chemistry, from fundamental biology to advanced materials science.