Question

Using a four-block periodic table as a guide, determine the ground-state electron configuration of krypton (Kr). Explain why it is proper for this element to be in group VIIIA.

Short answer

The ground-state electron configuration of krypton (Kr) is \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6\). Krypton belongs to Group VIIIA (noble gases) because its outermost energy level (n=4) is completely filled with electrons: \(4s^2 4p^6\), making it stable and similar to other noble gases in terms of properties.

Step-by-step solution

Identification of Krypton in the Periodic Table

Locate krypton (Kr) in the periodic table. Krypton has an atomic number of 36, meaning it has 36 electrons. It is found in Group VIIIA and Period 4.

Electron Configuration using Four-block Periodic Table

Using the four-block periodic table, the electron configuration of krypton can be determined as follows: 1s: Fill the first principal energy level (1s) with 2 electrons. \[1s^2\] 2s and 2p: Fill the second principal energy level (2s and 2p) with 8 electrons. \[2s^2 2p^6\] 3s and 3p: Fill the third principal energy level (3s and 3p) with 8 electrons. \[3s^2 3p^6\] 4s: Fill the fourth principal energy level (4s) with 2 electrons. \[4s^2\] 3d: Fill the 3d sublevel with 10 electrons. \[3d^{10}\] 4p: Fill the 4p sublevel with the remaining 6 electrons. \[4p^6\] Full electron configuration of krypton (Kr) is: \[1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6\]

Explain why Krypton is in Group VIIIA

Group elements in the periodic table have similar properties because they have the same number of electrons in their outermost energy level. The group VIIIA elements, also known as noble gases (He, Ne, Ar, Kr, Xe, and Rn), have full outer electron shells with 8 electrons (except for He, which has 2 electrons). In the case of krypton, its outermost energy level (n=4) has a full-threshold of electrons, 2 electrons in the 4s sublevel and 6 in the 4p sublevel: \[4s^2 4p^6\] This full set of outer shell electrons makes krypton stable and gives it the properties common to the elements in group VIIIA (noble gases). Thus, it is appropriate for krypton to belong to group VIIIA of the periodic table.

Key concepts

The Periodic Table

The Periodic Table is a systematic arrangement of the elements, ordered by their atomic number, electron configurations, and recurring chemical properties. Structures within the table - rows, columns, and blocks - highlight similarities between elements and are used to infer the behavior of an element, even if it's not well-studied.

Elements are arranged into periods (rows) that signify the principal energy level that is being filled with electrons, and groups or families (columns) that share similar electron configurations, particularly in their valence, or outermost, shells. The Periodic Table consists of four blocks – s, p, d, and f – which refer to the sublevel being filled with electrons in that section of elements.

Noble Gases

Noble gases make up Group VIIIA or Group 18 of the Periodic Table and are renowned for their remarkable stability. This family includes helium, neon, argon, krypton, xenon, and the radioactive radon. Unlike most other elements, noble gases possess a fully filled outer shell of electrons, allowing them very little reactivity under ordinary conditions.

The electronic configuration of noble gases is often used as a reference point in chemistry because these elements do not tend to gain or lose electrons. This complete valence shell configuration is described by the octet rule, which states that atoms are generally most stable when they have eight electrons in their valence shell. Helium is an exception, however, with only two electrons, which still constitutes a full shell for the first energy level.

Atomic Structure

At the center of atomic structure lies the nucleus, consisting of protons and neutrons. Surrounding the nucleus are electrons that exist in dizzily complex cloud-like regions called orbitals. These electrons are arranged in principal energy levels, and within those levels, further divided into sublevels (s, p, d, f).

The most stable and low energy state of an atom is called its ground state, and in this state, electrons fill orbitals starting from the lowest energy level, moving towards the highest. This is known as the Aufbau principle. The specific pattern of filling - first s, then p, then d, and finally f - provides an electron configuration that can be used to predict an element's chemical properties.

Ground-State Electron Configuration

A ground-state electron configuration is a term used to describe the arrangement of an atom's electrons into orbitals when the atom is in its lowest energy state. This configuration determines how the electrons are distributed across the different energy levels and sublevels (s, p, d, f) of the atom.

Krypton's configuration is an excellent example of how elements achieve a stable, ground-state configuration. By filling its outermost 4s and 4p sublevels, krypton attains a full octet, leading to a highly unreactive nature. Understanding the ground-state electron configuration is crucial in chemistry, as it explains an element's reactivity, formation of bonds, color, magnetism, and many other chemical properties.