Question

Refer to the periodic table and write the predicted electron configuration for each of the following elements: (a) B (b) Ti (c) Na (d) O (e) Ge (f) Ba (g) Pd (h) \(\mathrm{Kr}\)

Short answer

The electron configurations are: (a) B: \(1s^2 2s^2 2p^1\), (b) Ti: \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^2\), (c) Na: \(1s^2 2s^2 2p^6 3s^1\), (d) O: \(1s^2 2s^2 2p^4\), (e) Ge: \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^2\), (f) Ba: \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^6 6s^2\), (g) Pd: \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 4d^{10}\), (h) Kr: \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6\).

Step-by-step solution

Understand Electron Configuration Basics

Electron configurations are a way to represent the distribution of electrons in an atom's orbitals. Electrons fill orbitals in the order of increasing energy levels, following the pattern dictated by the Aufbau principle, Hund's rule, and the Pauli exclusion principle.

Recall the Order of Orbital Filling

The order of filling for orbitals can be summarized as: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p. This order is often visualized using a diagonal rule or an orbital filling diagram.

Electron Configuration for B

Boron (B) has an atomic number of 5. Its electron configuration is determined by filling the orbitals in the order of energy level format until all 5 electrons are used: \[ \text{B:}\ 1s^2\ 2s^2\ 2p^1 \]

Electron Configuration for Ti

Titanium (Ti) has an atomic number of 22. Its electrons fill up in the following order: \[ \text{Ti:}\ 1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^6\ 4s^2\ 3d^2 \]

Electron Configuration for Na

Sodium (Na) has an atomic number of 11. Its configuration is given by: \[ \text{Na:}\ 1s^2\ 2s^2\ 2p^6\ 3s^1 \]

Electron Configuration for O

Oxygen (O) has an atomic number of 8. The electron filling is:\[ \text{O:}\ 1s^2\ 2s^2\ 2p^4 \]

Electron Configuration for Ge

Germanium (Ge) has an atomic number of 32. Its configuration follows the order: \[ \text{Ge:}\ 1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^6\ 4s^2\ 3d^{10}\ 4p^2 \]

Electron Configuration for Ba

Barium (Ba) has an atomic number of 56. Its configuration is presented as: \[ \text{Ba:}\ 1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^6\ 4s^2\ 3d^{10}\ 4p^6\ 5s^2\ 4d^{10}\ 5p^6\ 6s^2 \]

Electron Configuration for Pd

Palladium (Pd) has an atomic number of 46. Its unique filling results in the configuration: \[ \text{Pd:}\ 1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^6\ 4s^2\ 3d^{10}\ 4p^6\ 4d^{10} \]

Electron Configuration for Kr

Krypton (Kr) has an atomic number of 36. Filling orbitals give: \[ \text{Kr:}\ 1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^6\ 4s^2\ 3d^{10}\ 4p^6 \]

Key concepts

Periodic Table

The periodic table is much like a map that guides us to understand the properties of elements, including their electron configurations. Each element on the periodic table is arranged according to its atomic number, which represents the number of protons—and fundamentally, the number of electrons—in a neutral atom. By observing the periodic table, we can predict the order in which electrons fill the orbitals of an element. This is due in part to its structured layout along periods (horizontal rows) and groups (vertical columns).
When we look at an element's position, we can determine the order of its electron configuration using a periodic approach. For instance, reading from top to bottom across each period indicates how electrons populate an element's orbitals, following a set sequence. In essence, the periodic table provides a blueprint for constructing the electron configuration of elements, showcasing patterns such as electronegativity, atomic size, and obviously, electron configuration as we move across or down the table.

Aufbau Principle

The Aufbau Principle is a fundamental concept in chemistry used to determine the electron configuration of atoms. The principle, which means "building-up" in German, describes how electrons fill the lowest energy orbitals first before progressing to higher energy levels. Think of it as filling a set of seats in a room, where seats (orbitals) closest to the door (lower energy) are filled first.
According to this principle, electrons are added one by one to the atom as we move to the next proton in the nucleus. By following the order of orbital filling, such as 1s before 2s, and 3p before 4s, this principle guides us in arranging electrons in a stable, low-energy configuration. The sequence of orbital filling uses the diagonal rule, where arrows indicate the pathway along which orbitals are filled. Consequently, the Aufbau Principle ensures that an atom's configuration is both grounded in reality and optimal energetically.

Hund's Rule

Hund's Rule helps us understand how electrons arrange themselves within an atom’s orbitals. While the Aufbau Principle tells us the order of filling, Hund's Rule offers insight on how electrons distribute across orbitals of equal energy, known as degenerate orbitals. This rule states that every orbital in a subshell is first singly occupied by electrons before any orbital is doubly occupied.
Imagine you have to seat passengers in a train with many empty seats of equal status—passengers tend to occupy separate seats unless compelled to share due to space constraints. Similarly, electrons prefer to spread out across different orbitals to minimize repulsion between negatively charged electrons. This maximizes the atom’s stability. Consequently, this rule is crucial for accurately predicting the electron configuration of elements, especially when dealing with elements in the p, d, and f blocks of the periodic table.

Pauli Exclusion Principle

The Pauli Exclusion Principle is key in understanding why electrons behave a certain way within atoms. Formulated by Wolfgang Pauli, this principle posits that no two electrons within an atom can have the same set of four quantum numbers. This effectively means that an orbital, which can host only two electrons, must have electrons with opposite spins.
Think of it like a bedroom where only two people can sleep, and they can only share if they have different needs—like one prefers the top bunk while the other prefers the bottom. This exclusion rule ensures that each electron in an atom maintains a unique identity by having a distinct set of characteristics. This principle is critical for determining the limit of electrons per orbital and influences how elements are organized on the periodic table. By ensuring no duplication in electron quantum numbers, the Pauli Exclusion Principle maintains the integrity and diversity of elements in chemistry.