Question

(a) What are "valence electrons"? (b) What are "core electrons"?(c) What does each box in an orbital diagram represent? (d) What quantity is represented by the direction (up or down) of the half-arrows in an orbital diagram?

Short answer

(a) Valence electrons are the electrons in the outermost energy level of an atom, determining its chemical properties and participation in chemical bonding. (b) Core electrons are the inner electrons that do not participate in chemical bonding but shield the nucleus's positive charge. (c) Each box in an orbital diagram represents an orbital, a region with high probability of finding an electron, and can hold a maximum of two electrons with opposite spins. (d) The direction of half-arrows in an orbital diagram represents the electron's spin, which can be either up (+1/2) or down (-1/2), following the Pauli Exclusion Principle.

Step-by-step solution

(a) Valence electrons)

Valence electrons are the electrons in the outermost energy level of an atom. They are important because they determine the chemical properties of an element and participate in chemical bonding with other elements. The number of valence electrons can be determined from the element's position in the periodic table. As we move across a period from left to right, the number of valence electrons increases.

(b) Core electrons)

Core electrons are the electrons that are not in the outermost energy level of an atom. They are found in the inner energy levels, closer to the nucleus, and do not participate in chemical bonding. Core electrons play a crucial role in shielding the positive charge of the nucleus, making it more difficult for valence electrons to be attracted by other atoms.

(c) Each box in an orbital diagram)

In an orbital diagram, each box represents an orbital, which is a region of space around an atom's nucleus where there is a high probability of finding an electron. An orbital can hold a maximum of two electrons, which have opposite spins. There are four types of orbitals: s, p, d, and f. The s orbital is spherical, while the p, d, and f orbitals have more complex shapes. Each energy level has a specific number of orbitals, and the different orbital types fill in a specific order according to increasing energy.

(d) Half-arrows in an orbital diagram)

In an orbital diagram, half-arrows represent individual electrons and their direction (up or down) represents the electron's spin. Spin is a quantum property of electrons, and it can either be up (+1/2) or down (-1/2). The Pauli Exclusion Principle states that no two electrons in an atom can have the same set of quantum numbers, which means that each orbital can hold a maximum of two electrons with opposite spins.

Key concepts

Understanding Core Electrons

Discovering the role of core electrons is crucial for students delving into atomic structure and chemistry. Unlike valence electrons which reside in the atom's outermost shell and engage in chemical reactions, core electrons inhabit the inner shells. These fundamental particles are key to an atom's identity, as they remain constant across chemical reactions, maintaining the atom's essence.

• Shielding effect: Core electrons play a pivotal part in the shielding effect, which helps to mitigate the pull of the positively charged nucleus on the valence electrons, influencing an atom's reactivity.
• Atomic stability: The presence of core electrons contributes to the stability of the atom, as they help to balance the positive charge of protons in the nucleus.

A reliable way to determine the number of core electrons is to subtract the number of valence electrons from the atom's total electron count. This understanding helps explain why core electrons are less involved in chemical bonding compared to their valence counterparts, due to their lower energy levels and proximity to the nucleus.

Deciphering the Orbital Diagram

An orbital diagram serves as a visual tool in quantum chemistry to depict the specific location of electrons around an atom's nucleus. The concept of orbitals is vital for grasping how atoms forge bonds and interact to form molecules.

• Energy levels and orbitals: Each energy level in an atom contains one or more sublevels, which in turn comprise orbitals. Orbitals are arranged in order of increasing energy: s, p, d, and f.
• Orbital capacity: An individual orbital can house up to two electrons. The s orbitals are spherical while p orbitals are dumbbell-shaped, and the more complex d and f orbitals have even more intricate geometries.

This orderly arrangement and maximum capacity rule stem from quantum mechanics principles. When filling in an orbital diagram, the lowest energy orbitals are filled first, progressing to higher energies. Hund's rule also advises that every orbital in a sublevel is singly occupied before any orbital is doubly filled, and all electrons in singly occupied orbitals have the same spin.

Electron Spin: A Quantum Phenomenon

The term electron spin may evoke the image of electrons spinning around an axis like planets; however, it's more abstract. In quantum mechanics, spin refers to a fundamental particle property related to its magnetic moment. This intrinsic property is central to understanding the behavior of electrons in atoms.

• Spin values: Electron spin is quantized and can have one of two possible values, typically represented as +1/2 (spin-up) or -1/2 (spin-down).
• Pauli Exclusion Principle: An important rule governing electron spin is this principle, which prohibits electrons within the same orbital from having identical quantum states. As a consequence, electrons paired in an orbital must have opposite spins.

The visualization of electron spin in an orbital diagram is achieved with up and down half-arrows. These half-arrows help one grasp the concept of electron pairing and the magnetic interactions in an atom. Recognizing the direction of electron spin aids in predictions about the magnetic properties of elements and their chemical bond formations.