Question

How many inner, outer, and valence electrons are present in an atom of each of the following elements? (a) \(\mathrm{O}\) (b) Sn (c) Ca (d) Fe (e) Se

Short answer

O: Inner: 2, Outer: 6, Valence: 6; Sn: Inner: 46, Outer: 4, Valence: 4; Ca: Inner: 18, Outer: 2, Valence: 2; Fe: Inner: 18, Outer: 8, Valence: 2; Se: Inner: 28, Outer: 6, Valence: 6

Step-by-step solution

Determine the atomic number of each element

The atomic number represents the number of protons (and electrons in a neutral atom). For the elements given: (a) O: 8 (b) Sn: 50 (c) Ca: 20 (d) Fe: 26 (e) Se: 34

Write the electron configuration for each element

Expand each atomic number into its full electron configuration to see the distribution of electrons into orbitals. O: 1s² 2s² 2p⁴ Sn: [Kr] 4d¹⁰ 5s² 5p² Ca: [Ar] 4s² Fe: [Ar] 3d⁶ 4s² Se: [Ar] 3d¹⁰ 4s² 4p⁴

Identify the inner and outer electrons

Inner electrons are those that are not in the outermost principal energy level; outer electrons are in the outermost principal energy level. O: Inner: 2 (1s²), Outer: 6 (2s² 2p⁴) Sn: Inner: 46 ([Kr]), Outer: 4 (5s² 5p²) Ca: Inner: 18 ([Ar]), Outer: 2 (4s²) Fe: Inner: 18 ([Ar]), Outer: 8 (3d⁶ 4s²) Se: Inner: 28 ([Ar] 3d¹⁰), Outer: 6 (4s² 4p⁴)

Determine the number of valence electrons

Valence electrons are the electrons involved in bonding, typically the outermost s and p electrons. O: Valence: 6 (2s² 2p⁴) Sn: Valence: 4 (5s² 5p²) Ca: Valence: 2 (4s²) Fe: Valence: 2 (4s²) or 8 including 3d electrons Se: Valence: 6 (4s² 4p⁴)

Key concepts

Inner Electrons

Inner electrons are those electrons that reside in the energy levels closer to the nucleus of an atom, effectively shielded from the external environment. They don't participate in chemical bonding. Inner electrons are also called core electrons. For instance, in an oxygen (O) atom with an electron configuration of 1s² 2s² 2p⁴, the inner electrons occupy the 1s orbital. This means oxygen has 2 inner electrons.
Elements often have several core electrons, depending on their position in the periodic table. Understanding inner electrons helps in differentiating them from valence and outer electrons, giving a clearer picture of an element's electron configuration.

Outer Electrons

Outer electrons are located in the outermost energy levels or shells of an atom. They are crucial in defining the atom's chemical properties and reactivity as they are more exposed to other atoms and can participate in forming chemical bonds. For example, in selenium (Se) with an electron configuration of [Ar] 3d¹⁰ 4s² 4p⁴, the electrons in the 4s² and 4p⁴ orbitals are considered outer electrons.
These outer electrons are more likely to interact during chemical reactions, providing important insight when predicting an element's behavior in various situations. Outer electrons are essential for understanding the external behaviors of atoms.

Valence Electrons

Valence electrons are the outermost electrons of an atom and are involved in forming bonds with other atoms. They determine an element's valency, which directly impacts chemical reactivity and bonding patterns. These electrons are usually found in the outermost s and p orbitals. For example, tin (Sn) with an electron configuration [Kr] 4d¹⁰ 5s² 5p², has 4 valence electrons, as the electrons in these outermost orbitals are crucial in chemical bonding.
Understanding valence electrons is paramount for predicting how elements combine to form compounds. It's the basis for creating chemical equations and understanding molecular structures.

Atomic Number

The atomic number of an element is the number of protons in the nucleus of an atom, and it's unique for each element. It also tells us the number of electrons in a neutral atom. For example, calcium (Ca) with an atomic number of 20, has 20 protons and, in its neutral state, also has 20 electrons.
By identifying the atomic number, one can determine the exact position of an element on the periodic table and infer its basic chemical properties. It plays a crucial role in understanding electron configurations and the overall structure of an atom.

Electron Distribution

Electron distribution refers to how electrons are distributed within an atom's different orbitals. It follows a specific order often described by the electron configuration notation. For example, iron (Fe) with an electron configuration of [Ar] 3d⁶ 4s², shows that its electrons are distributed in both the 3d and 4s orbitals after filling the Argon core.
Properly understanding electron distribution helps predict an element's chemical behavior. It illustrates how electrons fill available orbitals and helps in visualizing the arrangement of electrons around the nucleus, which is crucial for interpreting an element’s reactivity and bonding characteristics.