Question

Write full electron configurations and indicate the valence electrons and the core electrons for each element. (a) \(\mathrm{Kr}\) (b) \(\mathrm{Ge}\) (c) \(\mathrm{Cl}\) (d) \(\mathrm{Sr}\)

Short answer

Kr: 1s^22s^22p^63s^23p^64s^23d^104p^6 (Valence: 4p^6, Core: 1s^2 to 3d^10); Ge: 1s^22s^22p^63s^23p^64s^23d^104p^2 (Valence: 4s^2 4p^2, Core: 1s^2 to 3d^10); Cl: 1s^22s^22p^63s^23p^5 (Valence: 3s^2 3p^5, Core: 1s^2 to 2p^6); Sr: 1s^22s^22p^63s^23p^64s^23d^104p^65s^2 (Valence: 5s^2, Core: 1s^2 to 4p^6).

Step-by-step solution

Writing the electron configuration for Krypton (\text{Kr})

Identify the atomic number of Krypton from the periodic table, which is 36. Write down its electron configuration as follows: 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6. Core electrons are the ones in fully filled shells (1s to 3d), and the valence electrons are those in the highest energy shell, which for Krypton is the 4p electrons, even though they are also completely filled.

Writing the electron configuration for Germanium (\text{Ge})

Find the atomic number of Germanium, which is 32. The electron configuration is 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^2. The core electrons include fully filled shells up to 3d, and the valence electrons include the 4s and 4p electrons.

Writing the electron configuration for Chlorine (\text{Cl})

Chlorine's atomic number is 17, and its electron configuration is written as 1s^2 2s^2 2p^6 3s^2 3p^5. The core electrons are those from the 1s to the 2p level, and the valence electrons are in the 3s and 3p orbitals.

Writing the electron configuration for Strontium (\text{Sr})

Strontium has an atomic number of 38. Its electron configuration is 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6 5s^2. Core electrons include electrons up to 4p, while the valence electrons are those in the 5s orbital.

Key concepts

Valence Electrons

Valence electrons are the outermost electrons of an atom and are essential to understanding chemical reactions and bonds. These electrons have the highest energy levels and are typically found in the outer shell of an atom. They are crucial in determining an atom’s chemical properties, including how it interacts or bonds with other atoms. For example, in the element Chlorine (Cl), which has 17 electrons, the valence electrons are the 7 electrons in the 3s and 3p orbitals. These are the electrons involved when Chlorine forms bonds, such as in the creation of table salt (sodium chloride).

In general, elements in the same group of the periodic table have the same number of valence electrons, which explains why they often exhibit similar chemical behavior. For instance, all halogens (the group containing Chlorine) have seven valence electrons and typically form bonds by gaining an additional electron to achieve a full valence shell.

Core Electrons

In contrast to valence electrons, core electrons are the electrons in an atom that are not part of the outermost shell. These electrons are found in the inner shells and are not normally involved in chemical reactions or bonding. Core electrons serve an important role in shielding the positive charge of the nucleus from the valence electrons. This shielding effect influences how strongly the nucleus holds onto the valence electrons.

For example, in Strontium (Sr) with an atomic number of 38, the core electrons are the 36 electrons that fill up the orbitals from 1s up to 4p. The remaining two electrons in the 5s orbital are considered valence electrons. Core electrons essentially define the element's identity and are reflective of its position on the periodic table to the left of the valence electrons.

Periodic Table

The periodic table is a tabular arrangement of elements, organized on the basis of their atomic numbers, electron configurations, and recurring chemical properties. Elements are presented in order of increasing atomic number in rows known as periods. The columns, called groups or families, contain elements with similar properties and the same number of valence electrons. For instance, Group 1 elements are known as alkali metals and have a single valence electron, while Group 18 elements are noble gases with full valence shells.

The position of an element on the periodic table allows you to predict its chemical behavior, including how it bonds and interacts with other elements. Understanding the layout of the periodic table is key to knowing how to write electron configurations for different elements, as it provides a map that mirrors the filling order of the electron shells.

Atomic Number

The atomic number of an element is a fundamental concept in chemistry that represents the number of protons in the nucleus of an atom. This number is unique to each element and determines its position on the periodic table. For example, Krypton (Kr) has an atomic number of 36, meaning it has 36 protons in its nucleus.

Atomic numbers also tell us the number of electrons in a neutral atom, which in turn helps decipher the electron configuration. In all the elements, like Germanium (Ge) with its atomic number of 32, the atomic number guides us in knowing that there are 32 electrons arranged in occupied energy levels according to the rules of electron configurations. Therefore, the atomic number is paramount in identifying an element and understanding its chemical properties.