Question

(a) What are "valence electrons"? (b) What are "core electrons"? (c) What does each box in an orbital diagram represent? (d) What object is represented by the half arrows in an orbital diagram? What does the direction of the arrow signify?

Short answer

(a) Valence electrons are the outermost electrons in an atom, present in the highest-energy orbitals, and are responsible for the chemical properties and reactivity of an element. (b) Core electrons are the inner electrons, not involved in forming chemical bonds, but help in shielding the positive charge of the nucleus. (c) Each box in an orbital diagram represents an atomic orbital, which can hold a maximum of two electrons with opposite spins. (d) The half arrows in an orbital diagram represent electrons with a specific spin state, where 'up' arrow signifies spin +1/2 and 'down' arrow signifies spin -1/2.

Step-by-step solution

(a) What are "valence electrons"?

Valence electrons are the outermost electrons in an atom, which are present in the highest-energy orbitals. These electrons are responsible for the chemical properties of an atom and are involved in forming chemical bonds with other atoms. The number of valence electrons determines the reactivity of an element and their placement within the periodic table.

(b) What are "core electrons"?

Core electrons are the inner electrons of an atom, which are not involved in forming chemical bonds. These electrons are present in lower energy levels or orbitals and are closer to the nucleus than the valence electrons. Core electrons play a vital role in shielding the positive charge of the nucleus from the outer electrons, allowing valence electrons to be less strongly attracted to the nucleus and, therefore, more reactive.

(c) What does each box in an orbital diagram represent?

In an orbital diagram, each box represents an atomic orbital. An atomic orbital is a region of space around the nucleus of an atom where there is a high probability of finding an electron. Orbitals can have different shapes and energy levels depending on the type of orbital (s, p, d, or f) and the principal quantum number (n). Each box in the diagram can hold a maximum of two electrons with opposite spins.

(d) What object is represented by the half arrows in an orbital diagram? What does the direction of the arrow signify?

The half arrows in an orbital diagram represent electrons within the orbitals. The direction of the arrow signifies the electron's spin, which is a quantum mechanical property. There are two possible spin states for an electron, referred to as 'up' and 'down' or 'spin +1/2' and 'spin -1/2'. An 'up' arrow represents an electron with a spin of +1/2, while a 'down' arrow represents an electron with a spin of -1/2. In each orbital, there can only be one electron with a spin +1/2 and one electron with a spin -1/2 due to the Pauli Exclusion Principle, which states that no two electrons in the same atom can have identical quantum numbers.

Key concepts

Valence Electrons

Valence electrons are crucial when it comes to understanding the behavior of elements. These electrons are located in the outermost shell of an atom. Because they are the highest energy electrons, they have the easiest access to the outside world.
They directly influence an atom's ability to bond with other atoms. Consequently, valence electrons determine the chemical properties and reactivity of the element.

• The number of valence electrons can vary from 1 to 8 across different elements.
• For instance, oxygen has six valence electrons.

Getting a full set of valence electrons often leads to more stable configurations, which is why elements bond with each other – to achieve that octet formation seen in noble gases. Known as the octet rule, it further showcases the valence electrons' role in dictating chemical behavior.

Core Electrons

Core electrons can be thought of as the backbone of an atom. These are the electrons that reside in the inner shells or energy levels and are not involved in an atom's chemical bonding.

• They are closest to the nucleus and help shield the valence electrons from the strong positive charge within the nucleus.
• For example, in sodium, the 10 electrons in the first and second energy levels are considered core electrons.

This shielding effect reduces the effective nuclear charge experienced by valence electrons, making them more available for bonding. Understanding core electrons helps one grasp why and how valence electrons behave the way they do.

Orbital Diagram

An orbital diagram is a visual representation of the electron configurations of atoms. Each box or slot in these diagrams represents an atomic orbital, which is a region where there's a high probability of finding electrons.

• These orbitals can differ not only in shape but also in energy level.
• The four types of orbitals, s, p, d, and f, offer a diverse perspective on how atoms hold their electrons.

Each orbital can house up to two electrons, but those electrons must have opposite spins due to the Pauli Exclusion Principle. Hence, when drawing orbital diagrams, it's common to see two half arrows facing in opposite directions, portraying electrons within the same orbital.

Electron Spin

Electron spin is a fundamental property of electrons, akin to their charge and mass. This property doesn't correlate to a physical spinning of the electron but is rather an intrinsic attribute described in quantum mechanics.

• Spin comes in two possible states: 'up' (spin +1/2) and 'down' (spin -1/2).
• This duality is depicted in orbital diagrams using half arrows pointing up or down.

In an orbital, two electrons must have opposite spins, again due to the Pauli Exclusion Principle. This principle ensures that no two electrons in an atom can share the same set of quantum numbers, which helps define the unique structure and energy states of atoms in various elements.