Question

Write symbols, both with and without electron dots, for the ions formed by the following processes: (a) Gain of two electrons by selenium (b) Loss of two electrons by barium (c) Gain of one electron by bromine

Short answer

(a) Se²⁻: [:Se:] (with 2 extra dots), (b) Ba²⁺: [:Ba:], (c) Br⁻: [:Br:] (with one extra dot).

Step-by-step solution

Understanding Ion Formation

To form an ion, an atom gains or loses electrons. In (a), selenium gains electrons, becoming negatively charged. In (b), barium loses electrons, becoming positively charged. In (c), bromine gains an electron, becoming negatively charged.

Electron Configuration Review

For selenium (Se), the atomic number is 34, meaning it has 34 electrons when neutral. Barium (Ba) has an atomic number of 56. Bromine (Br) has an atomic number of 35.

Determine Charged Electrons

When selenium gains two electrons, it becomes Se^{2-}. Barium loses two electrons to become Ba^{2+}. When bromine gains one electron, it becomes Br^-.

Show Selenium Ion with Electron Dots

In Se^{2-}, selenium gains two electrons, adding them to the outer shell to achieve a filled electron configuration. The dot structure will show the additional two dots representing the extra electrons: [:Se:] with two additional electron dots for the added electrons.

Show Barium Ion with Electron Dots

Ba^{2+} loses two electrons, resulting in no valence electrons. The symbol for Ba^{2+} in electrons dots is [:Ba:], but without any additional dots, as it loses its valence electrons.

Show Bromine Ion with Electron Dots

Br^- gains one electron, achieving a full outer shell. The bromine ion is depicted with the symbol [:Br:], plus the additional electron dot to represent the gained electron.

Key concepts

Electron Configuration

Electron configuration describes how electrons are distributed in an atom's orbitals. It's like an address for electrons, helping us understand their arrangement around the nucleus.
For neutral atoms, the configuration is determined by the atomic number, which indicates the number of electrons. When atoms form ions, this configuration changes.

• For selenium (Se), with atomic number 34, the electron configuration is \([Ar] 3d^{10} 4s^2 4p^4\).
• When it gains two electrons to form \(Se^{2-}\), its new configuration becomes \([Ar] 3d^{10} 4s^2 4p^6\).
• Barium (Ba), with atomic number 56, has the configuration \([Xe] 6s^2\).
• After losing two electrons to form \(Ba^{2+}\), it becomes \([Xe]\), reflecting the removal of electrons from the outer shell.
• Bromine (Br) has \([Ar] 3d^{10} 4s^2 4p^5\), and gaining one electron turns it into \(Br^{-}\), with the configuration \([Ar] 3d^{10} 4s^2 4p^6\).

Ion Symbols

Ion symbols represent charged atoms, indicating how many electrons have been gained or lost. An ion symbol comprises the element's symbol, a superscript for the charge, and the number of electrons added or removed.

• For instance, \(Se^{2-}\) signifies selenium after gaining two electrons, becoming negatively charged.
• \(Ba^{2+}\) indicates barium losing two electrons, hence a positive charge.
• \(Br^{-}\) means bromine has gained one electron, acquiring a negative charge.

The superscripts clearly show whether the ion is positive or negative, aiding in understanding the changes in electron numbers during ion formation.

Valence Electrons

Valence electrons are the outermost electrons of an atom, crucial in forming chemical bonds and ions. These electrons determine the element's reactivity and ability to gain or lose electrons.

• Selenium has six valence electrons before gaining two more, resulting in a filled outer shell with eight electrons when it forms \(Se^{2-}\).
• Barium has two valence electrons initially, but losing both results in \(Ba^{2+}\) having no valence electrons.
• Bromine's seven valence electrons gain one more to complete its outer shell, forming \(Br^{-}\).

Understanding valence electrons can help predict how ions form during chemical reactions.

Electron Dot Structures

Electron dot structures, or Lewis dot diagrams, help visualize an element's valence electrons. These diagrams use dots around the element symbol to represent electrons.

• For \(Se^{2-}\), the structure is \(:Se:\), showing two extra dots added to selenium's usual six valence electrons, completing the outer shell with eight dots.
• \(Ba^{2+}\) is depicted as \(:Ba:\), without additional dots, as it has lost its valence electrons.
• \(Br^{-}\) appears as \(:Br:\), with one extra dot to illustrate the added electron completing the outer shell.

These visuals make understanding electron distribution in ions much simpler, aiding in the comprehension of chemical bonding and reactions.