Question

Use the periodic table to write electron configurations for each element. (a) Se (b) \(\mathrm{Sn}\) (c) \(\mathrm{Pb}\) (d) \(\mathrm{Cd}\)

Short answer

[Ar]4s2 3d10 4p4 for Se, [Kr]5s2 4d10 5p2 for Sn, [Xe]6s2 4f14 5d10 6p2 for Pb, and [Kr]5s2 4d10 for Cd.

Step-by-step solution

- Identify the Atomic Number

Find the atomic number of the element Se (selenium) on the periodic table. The atomic number corresponds to the number of protons and, in a neutral atom, also the number of electrons.

- Write Electron Configuration for Se

For Se with atomic number 34, the electron configuration is found by filling electrons in the order of the energy levels and sublevels: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p. Se fills up to the 4p level: df1:[Ar]4s23d104p4The notation [Ar] is used to signify the electron configuration of argon, which precedes selenium on the periodic table.

- Identify the Atomic Number for Sn

Find the atomic number of Sn (tin) on the periodic table to determine the number of electrons that need to be configured.

- Write Electron Configuration for Sn

For Sn with atomic number 50, the electron configuration will fill up to the 5p sublevel: [Kr]5s24d105p2Like with Se, [Kr] represents the electron configuration up to krypton.

- Identify the Atomic Number for Pb

Locate Pb (lead) on the periodic table to find its atomic number and determine the number of electrons.

- Write Electron Configuration for Pb

For Pb with atomic number 82, the electron configuration up to the 6p sublevel is: [Xe]6s24f145d106p2Here [Xe] denotes the electron configuration for xenon.

- Identify the Atomic Number for Cd

Search for Cd (cadmium) on the periodic table to know its atomic number which indicates the number of electrons to be placed in orbitals.

- Write Electron Configuration for Cd

For Cd with atomic number 48, the electrons are placed up to the 4d sublevel as follows: [Kr]5s24d10This makes use of the [Kr] configuration up to krypton.

Key concepts

The Periodic Table

The periodic table of elements is an essential tool for understanding the building blocks that make up matter. It is an organized chart where elements are arranged based on their atomic number, electron configurations, and recurring chemical properties. Each element is listed in a specific order, starting from the top left corner with the simplest (hydrogen) and increasing in complexity towards the bottom right.

Elements on the periodic table are placed into rows called periods and columns known as groups or families, which share common characteristics. For instance, elements within the same group typically share a similar number of valence electrons, influencing their chemical reactivity and bonding behaviors. As students navigate the periodic table, they gain insight into the patterns that govern the behavior of elements, such as trends in atomic radius, ionization energy, and electron affinity.

Atomic Number

The atomic number is a fundamental property of an element that defines its identity. It is equal to the number of protons found in the nucleus of an atom. Since protons carry a positive charge, the atomic number also determines the charge of the nucleus. In a neutral atom, the atomic number defines the total number of electrons orbiting the nucleus, as the number of electrons equals the number of protons to balance the electric charge.

This knowledge is crucial when writing electron configurations, as it tells you how many electrons you need to distribute among the energy levels. For instance, understanding that selenium (Se) has an atomic number of 34 means that a neutral Se atom contains 34 electrons that need to be arranged as per the rules governing electron configurations.

Energy Levels

Energy levels, often referred to as shells, are the probable locations around an atom's nucleus where electrons reside, governed by the quantum mechanical nature of electrons. An atom's electrons are arranged in these levels according to increasing energy, starting from the level closest to the nucleus.

The first energy level is closest to the nucleus and can hold up to 2 electrons. Subsequent levels can hold more, following a specific order dictated by quantum mechanics: 2, 8, 18, 32, etc. This pattern reflects the increasing complexity and energy of the orbitals that make up these levels. Electrons fill the lowest available energy levels before occupying higher ones. In writing electron configurations, correctly filling each energy level is imperative to accurately represent an atom's electron distribution.

Sublevels

Sublevels, also known as orbitals, are divisions within energy levels and further categorize where electrons are likely to be found. They come in four types: s, p, d, and f. Each type of sublevel can hold a different maximum number of electrons: s can hold 2, p can hold 6, d can hold 10, and f can hold 14.

Understanding the sequence of these sublevels is important when writing electron configurations. The order in which electrons fill these sublevels is defined by their increasing energy and is not necessarily sequential by energy level. For instance, the 4s sublevel is filled before the 3d sublevel, even though the latter comes first numerically. This means that when configuring selenium or tin, for example, one must ensure that the 4s sublevel is appropriately filled before progressing to the 3d.