Problem 88 - Introductory Chemistry Atoms First

Question

In which period and group in the periodic table are these atoms found? (a) \(1 s^{2} 2 s^{2} 2 p^{3}\) (b) \(1 s^{2} 2 s^{2} 2 p^{6} 3 s^{1}\) (c) \(1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{6} 4 s^{2} 3 d^{10} 4 p^{5}\)

Step-by-Step Solution

Answer

The elements with the given electronic configurations can be found in the following periods and groups: (a) 2nd period, 15th group (b) 3rd period, 1st group (c) 4th period, 17th group

Step 1: (a) Find period and group of \(1 s^{2} 2 s^{2} 2 p^{3}\)

To determine the period, identify the highest electron shell in the configuration, which in this case is the second shell (n = 2). The atom is in the 2nd period. To find the group, count the number of valence electrons. Valence electrons are the electrons in the outermost shell: \(2 s^{2} 2 p^{3}\) There are 2 electrons in the 2s orbital and 3 in the 2p orbital. Valence electrons: 2 + 3 = 5. The atom falls in the 15th group (as groups 13 - 18 correspond to p-block elements with 3 - 8 valence electrons)

Step 2: (b) Find period and group of \(1 s^{2} 2 s^{2} 2 p^{6} 3 s^{1}\)

To determine the period, identify the highest electron shell in the configuration, which in this case is the third shell (n = 3). The atom is in the 3rd period. For the group, count the number of valence electrons. Valence electrons are the electrons in the outermost shell: \(3 s^{1}\) There is 1 electron in the 3s orbital. Valence electrons: 1. The atom falls in the 1st group (as it has 1 valence electron)

Step 3: (c) Find period and group of \(1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{6} 4 s^{2} 3 d^{10} 4 p^{5}\)

To determine the period, identify the highest electron shell in the configuration, which in this case is the fourth shell (n = 4). The atom is in the 4th period. For the group, count the number of valence electrons. Valence electrons are the electrons in the outermost shell, which contains the 4s, 3d, and 4p orbitals. \( 4 s^{2} 3 d^{10} 4 p^{5}\) Valence electrons: 2 (from 4s) + 5 (from 4p) = 7. The atom falls in the 17th group (as groups 13 - 18 correspond to p-block elements with 3 - 8 valence electrons)

Key Concepts

Valence Electrons

Valence electrons are the electrons located in the outermost shell of an atom. They play a vital role in determining how an element reacts chemically with other elements. Knowing the number of valence electrons can help predict the molecule's chemical properties. For example:

• The more valence electrons an element has, the more likely it is to gain electrons in a reaction.
• If an element has fewer valence electrons, it is more likely to lose them.

In electron configurations, these electrons are situated in the highest electron shell. For instance, the configuration \(2s^2 2p^3\) shows that there are five valence electrons because the electrons are in the second shell (n=2).
Valence electrons also determine which group an element belongs to within the periodic table. For many p-block elements, the group number corresponds to the sum of the s and p electrons in their outermost shell. Understanding valence electrons is crucial for identifying chemical bonding and location in the periodic table groups.

Periodic Table Groups

Groups in the periodic table are vertical columns where elements share similar chemical and physical properties because they have the same number of valence electrons. These groups are numbered from 1 to 18, which helps in quickly identifying properties of elements, based on their group. Some key points about periodic table groups include:

• Group 1 elements are known as alkali metals and possess a single valence electron, making them highly reactive.
• Group 17 elements, called halogens, have seven valence electrons and are very reactive, often forming salts with group 1 elements.

Group numbers, particularly in the p-block (groups 13 to 18), represent the sum of s and p valence electrons. For instance, if an element falls into the 15th group, it will generally have five valence electrons. Recognizing the connection between valence electrons and groups can aid in predicting the behavior of elements.

Periodic Table Periods

Periods in the periodic table are the horizontal rows where elements have their valence electrons in the same principal energy level or shell. This row structure helps identify various properties and trends across the periodic table. The number of a period indicates how many electron shells an atom of an element in that period has. Consider these important characteristics of periods:

• Elements in the same period gradually change properties from metallic to non-metallic as you move across from left to right.
• As you move down a group to the next period, an additional electron shell is added, significantly affecting the size and reactivity of the elements.

In the periodic table, knowing an element belongs to a specific period helps determine the highest energy level of its valence electrons. For example, an element in the third period has its valence electrons in the third electron shell, represented by n=3, denoting higher energy levels.