Question

Refer to the periodic table and write the predicted electron configuration for each of the following elements: (a) $\mathrm{Li}$ (b) F (c) $\mathrm{Mg}$ (d) $P$ (f) $\mathrm{Mn}$ (g) Ga (h) $\mathrm{Rb}$

Short answer

The electron configurations are: Li: $1s^{2}2s^1$, F: $1s^{2}2s^{2}2p^5$, Mg: $1s^{2}2s^{2}2p^{6}3s^2$, P: $1s^{2}2s^{2}2p^{6}3s^{2}3p^3$, Mn: $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^5$, Ga: $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^1$, Rb: $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}5s^1$.

Step-by-step solution

Understand Electron Configuration

Electron configuration describes the distribution of electrons among different atomic orbitals in an atom. Elements fill orbitals starting from the lowest energy level, following the Aufbau principle, Pauli-exclusion principle, and Hund's rule.

Electron Configuration for Lithium (Li)

Lithium has 3 electrons. Following the order of filling, we fill the 1s orbital with 2 electrons and the 2s with 1 electron: $1s^{2}2s^1$.

Electron Configuration for Fluorine (F)

Fluorine has 9 electrons. The configuration is filled as follows: $1s^{2}2s^{2}2p^5$.

Electron Configuration for Magnesium (Mg)

Magnesium has 12 electrons. It fills the orbitals in the order: $1s^{2}2s^{2}2p^{6}3s^2$.

Electron Configuration for Phosphorus (P)

Phosphorus, with 15 electrons, fills the orbitals in this sequence: $1s^{2}2s^{2}2p^{6}3s^{2}3p^3$.

Electron Configuration for Manganese (Mn)

Manganese has 25 electrons. The electron configuration is: $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^5$.

Electron Configuration for Gallium (Ga)

Gallium has 31 electrons. Its electron configuration is: $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^1$.

Electron Configuration for Rubidium (Rb)

Rubidium has 37 electrons. The electron configuration is: $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}5s^1$.

Key concepts

Periodic Table

The periodic table is like a map for chemistry. It arranges all known chemical elements in a systematic way based on their atomic numbers, electron configurations, and recurring chemical properties.
This organization helps scientists understand the behavior of elements and predict how they might react in different situations.

• Rows and Columns: The horizontal rows are called periods and the vertical columns are called groups or families.
• Element Groups: Elements in the same group often have similar chemical properties because they have the same number of valence electrons.
• Atomic Number: As you move from left to right across a period, the atomic number increases, which means more protons and electrons are added.

The periodic table is essential for determining an element’s electron configuration because it shows the order in which atomic orbitals are filled. Each period begins filling a new principal energy level, which results in predictable patterns for electron configurations.

Aufbau Principle

The Aufbau principle is a crucial guideline in chemistry to determine the electron configurations of atoms.
The word "Aufbau" comes from German, meaning "building up" or "construction," which is fitting because it explains how electrons are added to atomic orbitals.

• Lowest to Highest Energy Levels: According to the Aufbau principle, electrons fill orbitals starting from the lowest available energy level before moving to higher levels.
• Order of Filling: The typical order is: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, and so on.
• Exceptions: Some transition metals exhibit exceptions to this rule due to similar energy levels between sub-shells, leading to special stability in half-filled or fully-filled d orbitals.

By following this principle, we can predict and write the electron configuration for most elements accurately. When combined with the periodic table, it allows for a clear roadmap of orbital filling.

Atomic Orbitals

Atomic orbitals are regions around a nucleus where electrons are most likely to be found. Each orbital can hold a maximum of two electrons with opposite spins.
These orbitals are part of the quantum mechanical model of atoms.

• Types of Orbitals: There are several types of orbitals: s, p, d, and f. The s-orbital is spherical, while p-orbitals are dumbbell-shaped. The d and f orbitals have even more complex shapes.
• Quantum Numbers: The position and energy of an electron within an atom are described using quantum numbers, which indicate the principal energy level, shape, and orientation of an orbital.
• Electron Shells and Subshells: Shells are made up of subshells. Each type of subshell can hold a specific number of electrons: s (2), p (6), d (10), and f (14).

Understanding orbitals helps explain the distribution of electrons in an atom, which in turn affects how an element interacts with others. This knowledge is foundational for predicting and understanding chemical reactions and bonding behaviors.