Question

Given below tre the names of few elements based on their position in the periodic table. Identify the element which is not correctly placed. (a) An element which tends to lose three electrons \- Aluminium (b) An element which tends to gain two electrons \- Iodine (c) An element with valency four-Silicon (d) A transuranium element - Plutonium

Short answer

Iodine is incorrectly placed as it should tend to gain one electron, not two.

Step-by-step solution

Analyze the Tendency to Lose Electrons

Elements that tend to lose electrons are typically metals which usually have 1, 2 or 3 electrons in their outer shell. Aluminium, with three valence electrons, tends to lose three electrons to achieve a stable octet, making it correctly placed.

Analyze the Tendency to Gain Electrons

Non-metals tend to gain electrons to fill their valence shell. Iodine, being a halogen, has seven valence electrons and tends to gain one electron to complete its octet, not two. This makes (b) Iodine incorrectly placed as it should be an element from the oxygen group that tends to gain two electrons.

Determining Valency

An element with a valency of four has four electrons in its outer shell and can either lose or gain four electrons to reach stability. Silicon, which is in group 14 of the periodic table, has four valence electrons and a valency of four, which means it is correctly placed.

Checking Transuranium Elements

Transuranium elements are those with atomic numbers greater than uranium (atomic number 92). Plutonium is indeed a transuranium element with atomic number 94, so it is correctly placed.

Key concepts

Understanding Electron Configuration

Electron configuration is the arrangement of electrons in the orbitals of an atom. It’s pivotal for understanding how atoms interact and bond with each other. The simplest model for electron configuration is the shell model, which organizes electrons in concentric rings around the nucleus, referred to as energy levels or shells. The innermost shell is the lowest in energy, and it fills up with electrons before the next shell begins to fill.

Each shell is subdivided into subshells designated s, p, d, f, and so on. These subshells explain why elements in the same group (vertical columns on the periodic table) have similar chemical properties; they have the same number of electrons in their outer subshell. For instance, Aluminium, with the electron configuration of \( 1s^2 2s^2 2p^6 3s^2 3p^1 \), has three electrons in its outermost shell and tends to lose those to achieve stability.

Element Valency and Chemical Reactions

Element valency is a critical concept reflecting an atom's ability to bond with other atoms. It refers to the number of electrons an atom can lose, gain, or share to become stable. Take silicon, for example, it has four electrons in its outer shell and can achieve stability by forming four covalent bonds, which manifests its tetravalency. It is crucial for students to grasp that valency directly impacts an element's chemical properties and its reactions.

Valency also often dictates the chemical formula of compounds formed by elements. In the case given, Silicon with a valency of four might form compounds like \( SiO_2 \) or \( SiC \), in which silicon shares electrons with oxygen or carbon, respectively, to fill up its outer shell.

Transuranium Elements

Transuranium elements are fascinating as they do not naturally occur on Earth and are synthesized in laboratories. These are the elements with atomic numbers greater than 92, which is uranium's atomic number.

Plutonium, mentioned in the textbook exercise, is one such element with an atomic number of 94. It is produced in nuclear reactors and has uses ranging from power generation to space exploration. These elements are typically very unstable and radioactive. The study of transuranium elements has pushed forward our understanding of nuclear reactions and the forces that hold the nucleus together.

It's important for students to understand that the existence of transuranium elements also underscores the vast potential of what can be synthesized beyond the naturally occurring elements found on Earth.