Problem 54 - Chemistry Matter and Change

Question

Discuss the formation of the barium ion.

Step-by-Step Solution

Answer

In summary, the barium ion (Ba^2+) is formed when barium, an alkaline earth metal with atomic number 56 and electron configuration \[1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 4s^{2} 3d^{10} 4p^{6} 5s^{2} 4d^{10} 5p^{6} 6s^{2}\], loses its two valence electrons in the 6s orbital to achieve a stable electron configuration similar to that of the noble gas xenon (\[1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 4s^{2} 3d^{10} 4p^{6} 5s^{2} 4d^{10} 5p^{6}\]). This results in a +2 cation denoted as Ba^2+.

Step 1: Electron configuration of Barium (Ba)

Barium is an alkaline earth metal with an atomic number of 56. In its ground state, barium has 56 electrons. The electron configuration of barium is \[1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 4s^{2} 3d^{10} 4p^{6} 5s^{2} 4d^{10} 5p^{6} 6s^{2}\]. Notice that the outermost shell, 6s, contains two valence electrons.

Step 2: Barium's tendency to form ions

Atoms tend to form ions in order to achieve a stable electron configuration, usually resembling that of the nearest noble gas. For barium, the nearest noble gas is xenon (Xe) with an electron configuration of \[1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 4s^{2} 3d^{10} 4p^{6} 5s^{2} 4d^{10} 5p^{6}\]. Barium can achieve this stable electron configuration by losing the two valence electrons in its 6s orbital.

Step 3: The ionization process

During ionization, barium loses its two valence electrons. The loss of these electrons results in more protons than electrons in the atom, creating a positive charge. Since barium loses two electrons, it forms a +2 cation (positively charged ion), which we denote as Ba^2+.

Step 4: The electron configuration of the barium ion (Ba^2+)

After losing two valence electrons, the electron configuration of the barium ion (Ba^2+) resembles that of the noble gas xenon. The electron configuration of Ba^2+ is \[1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 4s^{2} 3d^{10} 4p^{6} 5s^{2} 4d^{10} 5p^{6}\]. In summary, barium forms the barium ion (Ba^2+) by losing its two valence electrons to achieve a stable electron configuration similar to that of the noble gas xenon.

Key Concepts

Electron Configuration

The electron configuration of an atom is a representation of the arrangement of its electrons in orbitals around the nucleus. For Barium (Ba), with an atomic number of 56, the electrons are arranged in layers or shells that increase in energy from the innermost to the outermost. The configuration is noted as \[1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 4s^{2} 3d^{10} 4p^{6} 5s^{2} 4d^{10} 5p^{6} 6s^{2}\], which follows a specific sequence according to the Aufbau principle, the Pauli exclusion principle, and Hund's rule. These rules govern the sequence in which orbitals are filled. The 6s orbital, being the outermost layer, contains the valence electrons for Barium.

Ionization Process

The ionization process refers to the removal of one or more electrons from an atom, which results in the creation of an ion. For Barium, the ionization process involves the loss of two valence electrons to achieve a more stable state. Since Barium starts with 56 electrons and loses 2, the resulting barium ion has 54 electrons, making it a positively charged Ba^2+ ion. This occurs because the number of protons in the nucleus (56) now exceeds the number of remaining electrons (54), causing a net positive charge. The ionized Barium thus achieves an electron configuration that is identical to the noble gas Xenon, which is known for its stability.

Alkaline Earth Metals

Alkaline earth metals are a group in the periodic table that includes Barium, and they occupy the second group or column. These metals, which also encompass Beryllium, Magnesium, Calcium, Strontium, and Radium, all have two valence electrons in their outermost shell. This pair of electrons is typically lost or shared when they react, leading these elements to often carry a +2 charge in ionic compounds. Alkaline earth metals are known for their shiny, silvery-white appearance and their low electron affinity and low electronegativity, which is why they readily lose electrons during reactions.

Valence Electrons

Valence electrons are the outermost electrons of an atom and play a crucial role in chemical bonding and reactions. In the case of Barium (Ba), there are two valence electrons, both located in the 6s orbital. These are the electrons that are involved in bond formation and are also the electrons lost when Barium ionizes to form the Ba^2+ ion. The ease with which Barium loses these valence electrons to achieve a noble gas configuration makes it highly reactive and an agent for chemical bonding.