Question

Write the ground-state electron configuration, both full notation and noble gas abbreviation, and indicate the number of valence electrons for: (a) \(\mathrm{Al}\) (b) I (c) \(\mathrm{Rb}\) (d) \(\overline{\mathrm{Ar}}\) (e) \(\mathrm{Mg}\)

Short answer

(a) Al: Full electron configuration: \(1s^2 2s^2 2p^6 3s^2 3p^1\), Noble gas abbreviation: \(\mathrm{[Ne]} 3s^2 3p^1\), Valence electrons: 3. (b) I: Full electron configuration: \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^5\), Noble gas abbreviation: \(\mathrm{[Xe]} 5s^2 4d^{10} 5p^5\), Valence electrons: 7. (c) Rb: Full electron configuration: \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^1\), Noble gas abbreviation: \(\mathrm{[Kr]} 5s^1\), Valence electrons: 1. (d) Ar: Full electron configuration: \(1s^2 2s^2 2p^6 3s^2 3p^6\), Noble gas abbreviation: \(\mathrm{[Ar]}\), Valence electrons: 8. (e) Mg: Full electron configuration: \(1s^2 2s^2 2p^6 3s^2\), Noble gas abbreviation: \(\mathrm{[Ne]} 3s^2\), Valence electrons: 2.

Step-by-step solution

Full electron configuration for Al

Locate Al in the periodic table. It has the atomic number 13 which means it has 13 electrons. The electron configuration is: \[1s^2 2s^2 2p^6 3s^2 3p^1\]

Noble gas abbreviation

Find the nearest noble gas with fewer electrons than Al (Neon). Its electron configuration is: \[1s^2 2s^2 2p^6\] So the noble gas abbreviation for Al is: \[\mathrm{[Ne]} 3s^2 3p^1\]

Valence electrons

Valence electrons are found in the outermost shell. For Al, there are 3 valence electrons (3s^2 3p^1). (b) Iodine (I)

Full electron configuration for I

Locate I in the periodic table. It has the atomic number 53 which means it has 53 electrons. The electron configuration is: \[1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^5\]

Noble gas abbreviation

Find the nearest noble gas with fewer electrons than I (Xenon). Its electron configuration is: \[1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^6\] So the noble gas abbreviation for I is: \[\mathrm{[Xe]} 5s^2 4d^{10} 5p^5\]

Valence electrons

Valence electrons are found in the outermost shell. For I, there are 7 valence electrons (5s^2 5p^5). (c) Rubidium (Rb)

Full electron configuration for Rb

Locate Rb in the periodic table. It has the atomic number 37 which means it has 37 electrons. The electron configuration is: \[1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^1\]

Noble gas abbreviation

Find the nearest noble gas with fewer electrons than Rb (Krypton). Its electron configuration is: \[1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2\] So the noble gas abbreviation for Rb is: \[\mathrm{[Kr]} 5s^1\]

Valence electrons

Valence electrons are found in the outermost shell. For Rb, there is 1 valence electron (5s^1). (d) Argon (Ar)

Full electron configuration for Ar

Locate Ar in the periodic table. It has the atomic number 18 which means it has 18 electrons. The electron configuration is: \[1s^2 2s^2 2p^6 3s^2 3p^6\]

Noble gas abbreviation

Since Ar is a noble gas itself, the electron configuration serves as its own abbreviation: \[\mathrm{[Ar]}\]

Valence electrons

Valence electrons are found in the outermost shell. For Ar, there are 8 valence electrons (3s^2 3p^6). (e) Magnesium (Mg)

Full electron configuration for Mg

Locate Mg in the periodic table. It has the atomic number 12 which means it has 12 electrons. The electron configuration is: \[1s^2 2s^2 2p^6 3s^2\]

Noble gas abbreviation

Find the nearest noble gas with fewer electrons than Mg (Neon). Its electron configuration is: \[1s^2 2s^2 2p^6\] So the noble gas abbreviation for Mg is: \[\mathrm{[Ne]} 3s^2\]

Valence electrons

Valence electrons are found in the outermost shell. For Mg, there are 2 valence electrons (3s^2).

Key concepts

Valence Electrons

Valence electrons are the electrons found in the outermost shell of an atom, which determine its chemical properties and reactivity. These electrons play a crucial role in the bonding process since they can be lost, gained, or shared with other atoms to form chemical bonds. For example, in the case of aluminum (Al), which has the electron configuration \(1s^2 2s^2 2p^6 3s^2 3p^1\), the valence electrons would be those in the 3s and 3p orbitals, adding up to a total of three valence electrons.

Understanding the number of valence electrons an element has is key to predicting how it will interact with other elements. Elements in the same group of the periodic table have the same number of valence electrons, which accounts for the similarities in their chemical behavior. For instance, all noble gases have eight valence electrons (except for helium, which has two), making them very stable and unreactive.

Noble Gas Abbreviation

The noble gas abbreviation is a shorthand way to represent electron configurations of atoms, which simplifies the notation by substituting the core electron configuration with that of the nearest noble gas with fewer electrons. For example, rubidium (Rb) has the electron configuration \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^1\), but its noble gas abbreviation is \([Kr] 5s^1\), as krypton (Kr) is the noble gas that precedes Rb. This method is particularly useful for elements with many electrons, as it provides a more compact and readable format.

When using this abbreviation, it is assumed that the reader knows the electron configuration of the noble gases; hence only the electrons beyond that point are listed. This simplifies learning and writing configurations for elements, especially when dealing with transition metals or elements in higher periods which contain more subshells and electrons.

Periodic Table

The periodic table is a tabular display of all known chemical elements, organized by atomic number, electron configuration, and recurring chemical properties. Elements are arranged in order of increasing atomic number in rows called periods and columns known as groups or families. The periodic table is a powerful tool for predicting the chemical behavior of an element, as it categorizes elements with similar valence electron configurations into the same group.

For instance, elements in the first column, or Group 1, are known as the alkali metals and have one valence electron. Elements in Group 17 are the halogens, with seven valence electrons, which correspond to their high reactivity. The beauty of the periodic table lies in its ability to help us quickly deduce useful information such as valence electrons or the type of ion an element is likely to form based on its position, making it an essential reference for chemistry students and professionals alike.