Question

What are valence electrons? For main group elements, the number of valence electrons of an element is equal to its group number. Show that this is true for the following elements: \(\mathrm{Al}, \mathrm{Sr}, \mathrm{K}, \mathrm{Br}, \mathrm{P}, \mathrm{S}, \mathrm{C}\)

Short answer

For main group elements, the number of valence electrons is equal to their group number, which matches for Al, Sr, K, Br, P, S, and C as per their group placement.

Step-by-step solution

Understand Valence Electrons

Valence electrons are the electrons in the outermost electron shell of an atom. For main group elements, these are the electrons that are involved in chemical bonding. The number of valence electrons determines the chemical properties of an element.

Identify Group Numbers

Locate each element in the periodic table to identify its group number. Main group elements have their valence electrons equal to the group number in the periodic table.

Check Valence Electrons for Each Element

- **Aluminum (Al):** Group 13, so it has 3 valence electrons. - **Strontium (Sr):** Group 2, so it has 2 valence electrons. - **Potassium (K):** Group 1, so it has 1 valence electron. - **Bromine (Br):** Group 17, so it has 7 valence electrons. - **Phosphorus (P):** Group 15, so it has 5 valence electrons. - **Sulfur (S):** Group 16, so it has 6 valence electrons. - **Carbon (C):** Group 14, so it has 4 valence electrons.

Key concepts

Main Group Elements

The term 'main group elements' refers to the s- and p-block elements on the periodic table. These elements are crucial as they include all nonmetals, alkali metals, and alkaline earth metals, among others. They range from groups 1 and 2 on the left to groups 13 through 18 on the right.
These elements play a huge role in chemical biology and industrial processes due to their varied chemical properties and readiness to form various compounds. Their valence electrons are especially easy to understand—these electrons determine how they will bond chemically, bringing us to the next topic.

Periodic Table

The periodic table is like a high school seating chart of elements, offering a wealth of information at a glance. Each column is called a group, and each row is called a period. The elements are arranged in increasing atomic number, which is the number of protons in their nucleus.
Groups in the periodic table for main group elements are labeled from 1 to 18. This arrangement helps us easily determine properties like the number of valence electrons. By simply knowing an element's position, you can gather a simple yet thorough understanding of its chemical characteristics.

Chemical Bonding

Chemical bonding is the interaction that holds atoms together for the formation of compounds. The main types of chemical bonds are ionic, covalent, and metallic bonds. Valence electrons play an essential role in the process.
In covalent bonds, atoms share valence electrons, leading to molecule formation. In ionic bonds, atoms tend to give or take electrons to achieve a full valence shell, sometimes called an 'octet'. Understanding bonding helps in predicting how and why molecules are formed, and how they interact with each other.

Group Number

Group numbers are essentially labels for the columns of the periodic table. For main group elements, the group number is equal to the number of valence electrons in a neutral atom of that element. This holds true across several groups:

• For Group 1 elements, they have 1 valence electron.
• For Group 14 elements like Carbon, they have 4 valence electrons.
• For Group 17 like Bromine, they have 7 valence electrons.

This predictable pattern allows chemists to understand and predict the element's chemical properties based merely on its position on the table.

Chemical Properties

The chemical properties of an element refer to its propensity to undergo chemical changes or react with other elements. These properties are primarily determined by the number of valence electrons, which explain an element's tendency to gain, lose, or share electrons.
Knowing these properties, we can predict possible chemical reactions and understand the logical grouping of elements in the periodic table. For example, elements in Group 1 are highly reactive metals, while elements in Group 18 are noble gases, known for their lack of reactivity due to full valence shells.