Problem 3 - A Complete Resource Book in Chemistry for JEE Main

Question

The maximum valency of an element having atomic number seven is (a) 1 (b) 3 (c) 5 (d) 7

Step-by-Step Solution

Answer

The maximum valency of nitrogen (atomic number 7) is 5.

Step 1: Identify the Element

The atomic number given is 7. The atomic number determines the number of protons, and for neutral atoms, also the number of electrons. Thus, the element with atomic number 7 is nitrogen (N).

Step 2: Write the Electron Configuration

The electronic configuration of an element provides insight into the arrangement of electrons across different shells. For nitrogen, with atomic number 7, its electron configuration is \[1s^2 2s^2 2p^3\] This means nitrogen has 5 electrons in its outer shell (2s and 2p).

Step 3: Determine the Maximum Valency

Valency is the combining capacity of an element. Maximum valency is realized when all the outer shell electrons participate in bonding. For nitrogen, it can gain 3 electrons to complete its octet or it can lose/share its 5 outer electrons while bonding. Hence, the maximum valency is 5.

Key Concepts

Atomic Number

The atomic number is a crucial concept in chemistry, as it uniquely identifies each element on the periodic table. It represents the number of protons found in the nucleus of an atom. For neutral atoms, the atomic number also equals the number of electrons, because positively charged protons balance negatively charged electrons. This essential property determines an element's chemical behavior and its place on the periodic table.
For example, an atomic number of 7 corresponds to nitrogen, which means nitrogen atoms contain 7 protons and, thus, 7 electrons. Understanding the atomic number allows us to predict an element's electron configuration and, consequently, its chemical properties and reactions.

Electron Configuration

The electron configuration of an atom describes how electrons are distributed in its atomic orbitals. This is important because the arrangement of electrons determines the chemical properties and reactivity of the element.
Nitrogen, with an atomic number of 7, has an electron configuration of \[1s^2 2s^2 2p^3\]. This means that nitrogen's electrons fill the lower energy levels first—the "1s" orbital, followed by "2s," and then the "2p" orbitals.

• "1s" orbital is filled by 2 electrons.
• "2s" orbital is also filled by 2 electrons.
• "2p" orbital contains 3 electrons.

The outermost shell, known as the valence shell, is key in bonding because these are the electrons available for forming chemical bonds. In nitrogen, there are 5 valence electrons (2s and 2p combined), which play a significant role in its bonding behavior.

Chemical Bonding

Chemical bonding involves the interaction of atoms to achieve stable electron configurations. Nitrogen, with its 5 valence electrons in the \[2s^2 2p^3\] configuration, can achieve stability by forming chemical bonds, either by gaining, losing, or sharing electrons.

• Nitrogen often forms covalent bonds by sharing its valence electrons.
• To complete its octet, it can gain 3 additional electrons, often observed when nitrogen forms anions in ionic compounds.
• Alternatively, it can share its 5 valence electrons with other atoms, achieving a maximum valency of 5.

The maximum valency of an element corresponds to the number of valence electrons it can either gain, lose, or share in a chemical reaction. For nitrogen, this is particularly versatile, allowing it to participate in a wide range of chemical compounds and reactions.