Question

How many electrons does an Se atom have to gain to have a complete octet in its valence shell?

Short answer

A selenium atom needs 2 electrons to complete its octet.

Step-by-step solution

Understand the Octet Rule

The octet rule states that atoms gain, lose, or share electrons to have full sets of eight valence electrons like noble gases. An atom is stable when its outer shell is filled with eight electrons.

Identify Valence Electrons for Selenium

A selenium (Se) atom has an atomic number of 34, meaning it has 34 electrons in a neutral state. The electron configuration of Se is \(1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^2\, 3d^{10}\, 4p^4\). Its valence shell is the 4th shell, containing the 4s and 4p orbitals, which have a total of 6 electrons already.

Determine Electrons Needed for Full Octet

Since Se already has 6 electrons in its valence shell (4s^2, 4p^4), it needs 2 more electrons to fill the 4p orbital to achieve a complete octet (8 electrons).

Conclusion

To achieve a complete octet, a selenium atom must gain 2 more electrons to fill its valence shell.

Key concepts

Valence Electrons

Valence electrons are the outermost electrons of an atom and are crucial in determining how an element will react chemically. They are usually found in the outermost electron shell of an atom. These electrons are important because they interact in bonds, whether by sharing, gaining, or losing electrons, to fulfill the octet rule.

The octet rule is an essential guideline in chemistry that states atoms strive to have eight electrons in their valence shell, resembling the electron configuration of noble gases, which are inherently stable. For elements in groups 1 through 7 of the periodic table, having a complete set of eight valence electrons means reaching a low-energy, stable state.

Understanding valence electrons helps us predict the behavior of elements in chemical reactions. When you know how many valence electrons an atom has, you can easily determine whether an atom will donate, receive, or share electrons to achieve a full outer shell.

Electron Configuration

Electron configuration describes the arrangement of electrons in an atom. This configuration follows specific rules, filling energy levels and sublevels in a certain order. The rules are based on the principles of energy minimization, which ensures stability.

Each electron shell is divided into subshells labeled as s, p, d, and f. These subshells fill in a specific manner. For instance, s subshells can hold 2 electrons, p can hold 6, d can hold 10, and f can hold up to 14 electrons.

For selenium, with an atomic number of 34, the electron configuration is:

• (1s^2)
• (2s^2)
• (2p^6)
• (3s^2)
• (3p^6)
• (4s^2)
• (3d^{10})
• (4p^4)

This illustrates that selenium's valence shell is made up of the fourth shell containing electrons in the 4s and 4p orbitals. The focus is on the outermost 4s and 4p electrons because these are involved in chemical bonding.

Selenium Atom

A selenium atom, symbolized as Se, is a nonmetal element located in group 16 of the periodic table, often referred to as the oxygen family or chalcogens. Selenium has an atomic number of 34, which means it has 34 protons and, in its neutral state, an equal number of electrons.

The electronic configuration for selenium is important in understanding its chemical properties. Selenium’s configuration reveals that it has 6 valence electrons in its outer shell, given by the 4s and 4p orbitals. That is why it often forms compounds by gaining or sharing electrons to complete its octet. This characteristic aligns with the typical behavior of elements in the same group, like oxygen and sulfur.

In its natural state, selenium seeks to gain electrons to achieve a stable electron configuration. It requires 2 additional electrons to complete its octet, making it more likely to engage in reactions where it can accept electrons, such as in forming selenides with metals or in organic selenium compounds.