Problem 9 - Chemistry: The Central Science

Question

Write the electron configuration for phosphorus. Identify the valence electrons in this configuration and the nonvalence electrons. From the standpoint of chemical reactivity, what is the important difference between them?

Step-by-Step Solution

Answer

The electron configuration of phosphorus (atomic number 15) is 1s² 2s² 2p⁶ 3s² 3p³. There are 5 valence electrons (3s² 3p³) and 10 nonvalence electrons (1s² 2s² 2p⁶). The important difference in chemical reactivity between valence and nonvalence electrons is that valence electrons are more accessible and play a more significant role in chemical reactions and bonding, while nonvalence electrons are less likely to participate in chemical reactions due to their tighter bond to the nucleus.

Step 1: Write the electron configuration of phosphorus

To write the electron configuration of phosphorus, we must first know the atomic number of phosphorus, which is 15. This means there are 15 electrons in a neutral atom of phosphorus. Using the periodic table and the electron filling order (1s, 2s, 2p, 3s, 3p, 4s, 3d, ...), we can write the electron configuration. - 1s orbital can hold 2 electrons → 1s² - 2s orbital can hold 2 electrons → 2s² - 2p orbital can hold 6 electrons → 2p⁶ - 3s orbital can hold 2 electrons → 3s² - 3p orbital can hold the remaining 3 electrons → 3p³ Therefore, the electron configuration of phosphorus is 1s² 2s² 2p⁶ 3s² 3p³.

Step 2: Identify valence and nonvalence electrons

Valence electrons are the electrons in the outermost energy level (shell), while nonvalence electrons are located within the inner energy levels (shells). In our electron configuration for phosphorus (1s² 2s² 2p⁶ 3s² 3p³), the outermost energy level is n = 3. Thus, the valence electrons are in the 3s and 3p orbitals, which have 5 electrons in total (3s² 3p³). The nonvalence electrons are those in the inner energy levels (1s² 2s² 2p⁶), with a total of 10 electrons.

Step 3: Describe the important difference in chemical reactivity between valence and nonvalence electrons

The important difference between valence and nonvalence electrons when it comes to chemical reactivity is that valence electrons are more accessible because they are located in the outermost energy level. As a result, valence electrons play a more significant role in chemical reactions and bonding, as they can be easily gained, lost, or shared between atoms. On the other hand, nonvalence electrons are found in inner energy levels and are less likely to participate in chemical reactions, as they are more tightly bound to the nucleus and harder to remove from the atom.

Key Concepts

Electron Configuration

Electron configuration refers to the way electrons are arranged around the nucleus of an atom. Understanding the electron configuration of an atom like phosphorus helps reveal how electrons are distributed across different energy levels.
Phosphorus has an atomic number of 15, which signifies 15 electrons in a neutral phosphorus atom. Electrons are filled into different orbitals according to specific rules starting from the lowest energy level. Here are key steps in writing electron configurations:

• First, fill the 1s orbital, which holds up to 2 electrons: 1s².
• Next, fill the 2s orbital with 2 more electrons: 2s².
• The 2p orbital comes next and can contain up to 6 electrons: 2p⁶.
• The third energy level begins with the 3s orbital, holding 2 electrons: 3s².
• Finally, place the remaining 3 electrons into the 3p orbital: 3p³.

Thus, the electron configuration for phosphorus becomes 1s² 2s² 2p⁶ 3s² 3p³. This sequence details the arrangement of electrons, where each number and letter indicates the number of electrons and the type of orbital they occupy.

Chemical Reactivity

Chemical reactivity is largely influenced by the presence of valence electrons, which reside in the outermost shell of an atom and are crucial in forming chemical bonds. These electrons determine how an atom interacts with others.
Valence electrons can be gained, lost, or shared, meaning they play a pivotal role in chemical reactions. For example, phosphorus in the electron configuration 1s² 2s² 2p⁶ 3s² 3p³ has 5 valence electrons in the n=3 level (3s² 3p³).

• These 5 valence electrons define its reactivity and bonding with other elements.
• An atom like phosphorus tends to seek stability by filling its outer shell, leading to reactions where it might gain, lose, or share electrons.

In contrast, nonvalence electrons, nestled in inner shells, contribute less to chemical reactivity due to their proximity to the atom's nucleus, which binds them more strongly. Thus, their role in chemical bond formation is minimal.

Periodic Table

The periodic table is an essential tool in chemistry, organizing elements in a way that showcases recurring properties and trends. Understanding the placement of an element like phosphorus on the periodic table helps to predict its behavior, including electron configuration and chemical reactivity.
Phosphorus is located in period 3 and group 15 (or group VA), providing insights into its electron configuration and number of valence electrons. Here's how the periodic table aids in understanding elements:

• The period an element is in indicates the highest energy level an electron occupies, which for phosphorus is 3.
• The group number (in the main group elements) can show the number of valence electrons. Phosphorus, being in group 15, typically has 5 valence electrons.
• Elements in the same group often have similar reactivity due to having the same number of valence electrons.

Therefore, the periodic table isn't just a list of elements; it's also a map that aids in predicting chemical behavior and understanding elemental properties.