Question

Write full electron configurations for each element. (a) \(\mathrm{Sr}\) (b) Ge (c) \(\mathrm{Li}\) (d) \(\mathrm{Kr}\)

Short answer

The electron configurations are: (a) Sr: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2, (b) Ge: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p2, (c) Li: 1s2 2s1, (d) Kr: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6.

Step-by-step solution

- Identifying the Atomic Number

Determine the atomic number of each element from the periodic table: Sr (strontium) is 38, Ge (germanium) is 32, Li (lithium) is 3, Kr (krypton) is 36.

- Filling Atomic Orbitals

Using the Aufbau principle, fill the atomic orbitals in the order of increasing energy: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p. Continue until the number of electrons equals the atomic number of the element.

- Writing Electron Configurations for Sr

Sr (atomic number 38) fills orbitals in this order until all 38 electrons are placed: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2.

- Writing Electron Configurations for Ge

Ge (atomic number 32) fills orbitals in this order until all 32 electrons are placed:1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p2.

- Writing Electron Configurations for Li

Li (atomic number 3) fills orbitals in this order until all 3 electrons are placed: 1s2 2s1.

- Writing Electron Configurations for Kr

Kr (atomic number 36) fills orbitals in this order until all 36 electrons are placed:1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6.

Key concepts

Aufbau Principle

Understanding the Aufbau principle is essential for grasping how electrons fill atomic orbitals. Aufbau, German for 'building up', refers to the rule that electrons occupy the lowest energy orbital available before moving to higher energy levels.

Think of this like filling up a hotel from the lower to the upper floors. Each room represents an orbital, and electrons are the guests. The 1s orbital is the first 'room' to be filled, akin to the ground floor. Electrons will fill this room before moving to the second floor (2s), then to the second floor's larger suite (2p), and so on.

Following this process will give you the electron configuration of an element, which shows where the electrons are within an atom. By knowing the electron configuration, one can predict chemical reactivity and bonding behavior.

Atomic Orbitals

Atomic orbitals are the 'rooms' in our metaphorical hotel where electrons reside. They are not just boxes to check off, but complex shapes that describe where an electron is likely to be found in an atom. The shapes—spherical (s), dumbbell (p), cloverleaf (d), and complex (f)—correspond to various energy levels.

Basic Types of Orbitals

• s-Orbitals: Spherical shape, one per energy level.
• p-Orbitals: Dumbbell shape, three orientations per energy level (after the 1s).
• d-Orbitals: Cloverleaf shape, five orientations (starting from the 3rd energy level).
• f-Orbitals: More complex shapes, seven orientations (starting from the 4th energy level).

It's the interplay of these orbitals' shapes and energies that dictate how electrons fill them according to the rules of the Aufbau principle and other electron configuration principles, like Pauli exclusion principle and Hund's rule.

Periodic Table

The periodic table is not just a chart; it's a powerful tool that summarizes the entire discipline of chemistry. It organizes elements by increasing atomic number—that is, the number of protons in an atom's nucleus, which also tells us the number of electrons in a neutral atom. The layout of the table is designed to showcase patterns in electron configuration and hence in chemical behavior.

The rows, known as periods, indicate the number of electron shells. Moving from left to right across a period, each element has one more electron and is one step further in filling its outer shell. Meanwhile, the columns, called groups or families, possess similar electron configurations in their outer shell, which accounts for their similar chemical properties.

Atomic Number

An element's atomic number is the cornerstone to understanding its electron configuration. Simply put, the atomic number is the number of protons in an atom's nucleus, and by extension, it's the number of electrons in a neutral atom.

So, if you're peeking at the periodic table and you see hydrogen with an atomic number of 1, it has one electron to place in orbitals. Uranium, on the other hand, with an atomic number of 92, has a total of 92 electrons to distribute according to the rules of electron configuration. The atomic number not only locates an element on the periodic table but also guides us through the process of writing out the electron configuration, from the humble hydrogen to the complex heavy elements.