Question

Write the full electron configuration \(\left(1 s^{2} 2 s^{2},\right.\) etc. \()\) for each of the following elements. a. bromine, \(Z=35\) b. xenon, \(Z=54\) c. barium, \(Z=56\) d. selenium, \(Z=34\)

Short answer

a. Bromine: \(\mathrm{1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{5}}\) b. Xenon: \(\mathrm{1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}5s^{2}4d^{10}5p^{6}}\) c. Barium: \(\mathrm{1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}5s^{2}4d^{10}5p^{6}6s^{2}}\) d. Selenium: \(\mathrm{1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{4}}\)

Step-by-step solution

a. Bromine (Z=35)

According to the Aufbau Principle, we can build the electron configuration of bromine by filling the subshells in the respective order until all the 35 electrons are accounted for. Bromine electron configuration: \(\mathrm{1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{5}}\)

b. Xenon (Z=54)

Following the Aufbau Principle, we can add electrons to appropriate subshells for Xenon until all 54 electrons have been assigned. Xenon electron configuration: \(\mathrm{1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}5s^{2}4d^{10}5p^{6}}\)

c. Barium (Z=56)

Using the Aufbau Principle, we can determine the full electron configuration for Barium by filling the subshells in order until all 56 electrons are in place. Barium electron configuration: \(\mathrm{1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}5s^{2}4d^{10}5p^{6}6s^{2}}\)

d. Selenium (Z=34)

Following the Aufbau Principle, we will distribute the 34 electrons of Selenium among the subshells. Selenium electron configuration: \(\mathrm{1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{4}}\)

Key concepts

Aufbau Principle

The Aufbau Principle is a foundational concept that lays the ground rules for building up the electron configuration of an atom. It is based on the principle that electrons occupy the lowest energy orbitals first. In simpler terms, think of it as a rule where electrons fill up 'seats' in an auditorium starting from the front rows (lower energy levels) before moving to the back rows (higher energy levels).

According to the Aufbau Principle, subshells are filled in a specific sequence: 1s, 2s, 2p, 3s, and so on. The 's', 'p', 'd', and 'f' indicate different shapes of the orbitals and the numbers represent the energy levels. Electrons are added one at a time, following certain rules like the Pauli exclusion principle and Hund's rule, ensuring that no orbital has more than two electrons and that they are added to different orbitals of the same subshell in a way that maximizes the number of unpaired electrons.

For example, the electron configuration of Bromine (Br) with an atomic number of 35 follows this principle step-by-step until every orbital up to 4p has been filled to accommodate all 35 electrons.

Periodic Table

The periodic table is not just a chart; it's the ultimate cheat sheet for understanding atomic structure and predicting chemical behaviors. Each element in the periodic table is arranged according to its atomic number, which is the number of protons in its nucleus. Rows, or periods, tell us the number of electron shells in an atom, and columns, known as groups, indicate the number of electrons in the outer shell.

For those delving into electron configurations, the periodic table provides a visual roadmap. Elements are grouped into 'blocks'—'s', 'p', 'd', and 'f'—corresponding to the last subshell that was filled with electrons. The position of an element thus gives you clues to write its electron configuration. As you move across a period, electrons are added one after another to these subshells. The noble gases, for instance, all end with a full 'p' subshell, which makes them particularly stable, a fact reflected in their lack of reactivity.

Atomic Structure

Diving deep into atomic structure is like exploring a tiny universe. At the center is the nucleus, composed of protons and neutrons, around which electrons move in defined regions called orbitals. In contrast to older models that depicted electrons circling the nucleus like planets around the sun, modern quantum mechanics describes orbitals as areas where there is a high chance to find an electron.

Electrons are arranged in shells around the nucleus, and each shell can hold a set number of electrons. When the first shell is full, it resembles a simple sphere. As additional electrons are added to an atom, they go into more complex orbitals in each new shell, creating an intricate and layered atomic structure.

Fundamental to understanding the atomic structure is mastering the concepts of subatomic particles and electron configurations, which foreshadow the bonding and interactions that explain the vast majority of chemical phenomena. For instance, selenium (Se) with an atomic number of 34 organizes its electrons in several shells up to the 4p orbital, which shapes its properties and how it interacts with other elements.