Question

Using the symbol of the previous noble gas to indicate the core electrons, write the valence shell electron configuration for each of the following elements. a. phosphorus, \(Z=15\) b. chlorine, \(Z=17\) c. magnesium, \(Z=12\) d. \(\operatorname{zinc}, Z=30\)

Short answer

The valence shell electron configurations for the given elements are as follows: a. Phosphorus (Z=15): \([\textrm{Ne}](3s^2 3p^3)\) b. Chlorine (Z=17): \([\textrm{Ne}](3s^2 3p^5)\) c. Magnesium (Z=12): \([\textrm{Ne}](3s^2)\) d. Zinc (Z=30): \([\textrm{Ar}](3d^{10} 4s^2)\)

Step-by-step solution

1. Identify the Previous Noble Gas

Look in the periodic table for the noble gas that comes right before the given element. This will be the "core" electrons. Noble gases are located in Group 18.

2. Determine the Valence Shell Electrons

The electrons in the outermost shell are the valence electrons. Use the atomic number (Z) to determine the number of electrons and distribute them in the subshells (s, p, d, f) according to their order.

3. Write the Valence Shell Electron Configuration

Using the symbol of the previous noble gas and the valence shell electrons configuration, write the final electron configuration for the given element. a. Phosphorus (Z=15)

- Identify the Previous Noble Gas

(Ne) is the noble gas before phosphorus.

- Determine the Valence Shell Electrons

Phosphorus has 5 valence electrons. Distribute them in the subshells: \(3s^2 3p^3\)

- Write the Valence Shell Electron Configuration

\([\textrm{Ne}](3s^2 3p^3)\) b. Chlorine (Z=17)

- Identify the Previous Noble Gas

(Ne) is the noble gas before chlorine.

- Determine the Valence Shell Electrons

Chlorine has 7 valence electrons. Distribute them in the subshells: \(3s^2 3p^5\)

- Write the Valence Shell Electron Configuration

\([\textrm{Ne}](3s^2 3p^5)\) c. Magnesium (Z=12)

- Identify the Previous Noble Gas

(Ne) is the noble gas before magnesium.

- Determine the Valence Shell Electrons

Magnesium has 2 valence electrons. Distribute them in the subshells: \(3s^2\)

- Write the Valence Shell Electron Configuration

\([\textrm{Ne}](3s^2)\) d. Zinc (Z=30)

- Identify the Previous Noble Gas

(Ar) is the noble gas before zinc.

- Determine the Valence Shell Electrons

Zinc has 12 valence electrons. Distribute them in the subshells: \(3d^{10} 4s^2\)

- Write the Valence Shell Electron Configuration

\([\textrm{Ar}](3d^{10} 4s^2)\)

Key concepts

Noble Gases

Noble gases are a group of naturally occurring elements found in Group 18 of the periodic table. These elements include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). They are known for their stability and very low chemical reactivity. This is because noble gases have complete electron shells, making them unlikely to react with other elements.

In terms of electron configuration, a noble gas configuration describes the full outer shell of electrons. For instance, neon \(Ne\) has a configuration of \(1s^2 2s^2 2p^6\), meaning its outer shell is fully occupied. When writing electron configurations for other elements, the symbol of the nearest noble gas prior to the element in question is used to indicate the core electrons. This simplifies the electron configuration and focuses on the valence electrons, which are critical in chemical reactions.

For example, for phosphorus \(Z=15\), you would use the noble gas neon \(Ne\) as a starting point, before adding the necessary valence electrons: \([\text{Ne}]3s^2 3p^3\).

Core Electrons

Core electrons are those electrons residing in the inner shells of an atom, which are not involved in chemical bonding or reactions. These electrons are shielded from interaction by the outer shell electrons, called valence electrons. Understanding the distinction between core and valence electrons is crucial in predicting how elements will interact with each other.

In chemical notation, core electrons are often represented by the symbol of the nearest noble gas preceding the element in the periodic table. This shorthand method provides a clearer focus on the valence electrons, which are typically responsible for the chemical properties of the element.

For instance, with magnesium \(Z=12\), the symbol \(\text{Ne}\) indicates the presence of core electrons up to the configuration \(1s^2 2s^2 2p^6\). The magnesium atom has additional electrons, specifically two valence electrons that are situated in the outermost shell as \(3s^2\). This configuration impacts how magnesium would react chemically with other elements.

Periodic Table

The periodic table is a comprehensive chart that organizes all known chemical elements according to increasing atomic number, electron configuration, and recurring chemical properties. Elements are arranged in rows called periods and columns called groups, which show trends in element properties.

The periodic table provides a valuable framework for understanding element behavior. It allows you to identify elements that share common properties and predict how different elements might interact.

For example, noble gases fall into Group 18, characterized by full valence electron shells. This precise arrangement gives them their distinctive non-reactivity, whereas elements immediately before the noble gases have one less electron, making them highly reactive (e.g., fluorine in Group 17). Understanding the layout of the periodic table is crucial for mastering chemistry principles and grasping how elements vary across the tables.

Electron Subshells

Electron subshells refer to subdivisions within electron shells of an atom. Each subshell type is represented by the letters s, p, d, and f, which signify different shapes and capacities for holding electrons. The distribution of electrons across these subshells determines the atom's electron configuration.

For atoms, electrons fill lower energy subshells first before moving to higher ones. Each type of subshell has a specific capacity:

• s holds up to 2 electrons,
• p holds up to 6 electrons,
• d holds up to 10 electrons,
• and f can hold up to 14 electrons.

For instance, the electron configuration for zinc \(Z=30\) utilizes subshells up to the \(4s\) and \(3d\) subshells: \([\text{Ar}]3d^{10}4s^2\). Understanding electron subshells is vital for predicting chemical bonding and reactivity patterns in atoms.