Question

Write full electron configurations and indicate the valence electrons and the core electrons for each element. (a) \(\mathrm{Sb}\) (b) \(\mathrm{N}\) (c) \(\mathrm{B}\) (d) \(\mathrm{K}\)

Short answer

Full configurations: (a) Sb: [Kr]4d^105s^25p^3, Valence: 5, Core: 46. (b) N: 1s^22s^22p^3, Valence: 5, Core: 2. (c) B: 1s^22s^22p^1, Valence: 3, Core: 2. (d) K: [Ar]4s^1, Valence: 1, Core: 18.

Step-by-step solution

Determine Electron Configurations

Use the periodic table to determine the electron configurations of Sb, N, B, and K. The order of filling is based on the Aufbau principle, which follows the sequence: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, etc. Start from hydrogen and follow the periods and groups to achieve the full electron configuration.

Write Electron Configurations for Each Element

Write out the electron configurations based on the sequence obtained from the periodic table. For Sb, the atomic number is 51 and the configuration is [Kr]4d^105s^25p^3. For N with atomic number 7, the configuration is 1s^22s^22p^3. For B with atomic number 5, the configuration is 1s^22s^22p^1. For K with atomic number 19, the configuration is [Ar]4s^1.

Identify Valence Electrons

Valence electrons are the electrons in the outermost shell (highest energy level). For Sb, valence electrons are 5s^25p^3 - a total of 5. For N, valence electrons are 2s^22p^3 - a total of 5. For B, valence electrons are 2s^22p^1 - a total of 3. For K, valence electrons are 4s^1 - a total of 1.

Identify Core Electrons

Core electrons are all the electrons that are not valence electrons. For Sb, there are 46 core electrons ([Kr]4d^10). For N, there are 2 core electrons (1s^2). For B, there are 2 core electrons (1s^2). For K, there are 18 core electrons ([Ar]).

Key concepts

Valence Electrons

Understanding valence electrons is crucial for anyone studying chemistry, as they play a pivotal role in chemical reactions and bonding. Valence electrons are the outermost electrons of an atom and are responsible for the chemical properties of the element. They are located in the atom's highest energy level, or outer shell, which is what interacts with other atoms during chemical reactions.

When looking at the periodic table, you can determine the number of valence electrons an element has by its group number. For example, elements in group 1 have 1 valence electron, while group 2 elements have 2 valence electrons. In the case of transition metals, it's a bit more complex, but generally, the number of valence electrons corresponds to the number of electrons in the incomplete outermost shell. This is crucial for predicting how elements will interact with one another.

Core Electrons

In contrast to valence electrons, core electrons are the electrons that are not in the outermost shell of an atom. They are found in the energy levels below the valence shell and are not typically involved in chemical bonding or reactions. Core electrons are essentially the inner layers of 'clouds' of electrons that shield the valence electrons from the attractive force of the positively charged nucleus.

This shielding effect explains why atoms with the same number of valence electrons, but a different number of core electrons, can have quite different chemical properties. For example, sodium (Na) and potassium (K) both have one valence electron, but potassium has more core electrons, making it larger and more reactive.

Aufbau Principle

The Aufbau principle is a foundational guideline in chemistry for determining an element's electron configuration. The name 'Aufbau' is German for 'building up' as this principle involves building up the electron configuration of an element by progressively adding electrons to the lowest energy orbitals first. According to this principle, electrons occupy orbitals starting at the lowest available energy state before filling higher states.

The specific order in which subshells are filled is determined by their combined principal quantum number and orbital quantum number. The Aufbau principle, together with Pauli's Exclusion Principle and Hund's Rule, helps us predict the electronic structure of an atom. This orderly process allows chemists to understand and predict the chemical and physical properties of the elements.

Periodic Table

The periodic table is more than just a chart; it's a powerful tool that encapsulates the essence of chemistry. It organizes all known elements in a meaningful way, highlighting their properties and how they relate to one another. Each element is positioned in a specific order based on its atomic number (the number of protons in its nucleus).

The table is arranged in rows (called periods) and columns (called groups) that reveal much about an element's characteristics. Elements in the same group have similar chemical and physical properties due to having the same number of valence electrons. The periodic table is extremely valuable for predicting an element's behavior in chemical reactions, understanding trends in element properties, and defining electron configurations, as seen in the exercise provided.