Problem 6 - A Complete Resource Book in Chemistry for JEE Main

Question

The elements with atomic numbers \(9,17,35,53\) and 85 (a) noble gases (b) light metals (c) halogens (d) heavy metals

Step-by-Step Solution

Answer

The elements are halogens.

Step 1: Identify the Category

First, identify which group in the periodic table corresponds to the atomic numbers given: 9, 17, 35, 53, and 85. These elements are listed in numerical order, corresponding to elements fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At) respectively.

Step 2: Determine the Group Properties

These elements are all in Group 17 of the periodic table. Group 17 elements are known as halogens, which are characterized by their high reactivity and are typically non-metals. Halogens are known for forming salts when they react with metals.

Step 3: Rule Out Other Groups

Noble gases (a) are in Group 18 and consist of helium, neon, argon, krypton, xenon, and radon, none of which match the given atomic numbers. Light metals (b) are typically found in Groups 1 and 2. Heavy metals (d) are often transition or post-transition metals, which are neither the elements nor characteristic of the given numbers.

Step 4: Choose the Correct Category

Based on the elemental atomic numbers and their classification as halogens, the correct category for all given elements is halogens (c).

Key Concepts

Periodic Table

The periodic table is a systematic arrangement of all known chemical elements, structured based on atomic numbers, electron configurations, and recurring chemical properties. Each element has a unique position based on these attributes. The most basic unit of this structure is the atomic number, which is simply the number of protons in an atom's nucleus.

Elements are organized into columns called groups and rows called periods. Groups contain elements that have similar properties. Each element in a group has the same number of electrons in its outermost shell, leading to similar chemical behavior. For example, all elements in Group 17, known as halogens, have similar characteristics because they all have seven valence electrons.

• Periods are horizontal rows indicating the number of electron shells around the nucleus of the elements.
• Groups are vertical columns that exhibit how elements react with other substances.

This organizational structure of the periodic table helps chemists quickly derive information about elemental properties and predict chemical reactions.

Group 17 Elements

Group 17 elements, also known as halogens, include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). These elements occupy the second-to-last column in the periodic table and exhibit very distinct and highly reactive properties due to their electron configuration. Halogens are unique in that they need just one more electron to achieve a full outer shell, making them very eager to engage in chemical reactions.

Most halogens exist in diatomic form, meaning that they occur naturally as molecules consisting of two atoms. This diatomic nature is a product of their high reactivity and desire to achieve stability.

• Fluorine and chlorine are gases at room temperature.
• Bromine is a liquid.
• Iodine and astatine are solids.

This variation in physical state at room temperature is another interesting facet of the halogens, showcasing their wide range of behaviors despite belonging to the same group.

Chemical Properties of Halogens

Halogens are best known for their strong tendency to form salts with metals, a process that results from their high reactivity and electronegativity. Electronegativity refers to an atom's ability to attract and hold onto electrons. Halogens have some of the highest electronegativity values on the periodic table, especially fluorine, which is the most electronegative element known.

Because of this tendency to attract electrons, halogens readily form ionic bonds with metals. An example of this is the formation of sodium chloride (table salt), where chlorine (a halogen) gains an electron from sodium, resulting in ions that stack together to form a solid crystal.

• They also form covalent bonds with nonmetals, sharing electrons to make molecules like hydrogen chloride (HCl).
• Halogen compounds are indispensable in industrial applications, including water purification and in the production of plastics.

Additionally, halogens often undergo displacement reactions where a more reactive halogen can displace a less reactive one from a compound. This reactivity pattern helps chemists understand trends and predict chemical behavior.