Question

Write the group number and the electron arrangement for each of the following: a. magnesium b. chlorine C. beryllium d. argon

Short answer

Mg: Group 2, 2,8,2; Cl: Group 17, 2,8,7; Be: Group 2, 2,2; Ar: Group 18, 2,8,8.

Step-by-step solution

- Identify the atomic number

Find the atomic number for each element from the periodic table. Magnesium (Mg) has an atomic number of 12, chlorine (Cl) is 17, beryllium (Be) is 4, and argon (Ar) is 18.

- Determine the electron configuration

Use the atomic number to determine the electron arrangement for each element. For instance, magnesium has 12 electrons arranged as 2, 8, 2; chlorine has 17 electrons arranged as 2, 8, 7; beryllium has 4 electrons arranged as 2, 2; argon has 18 electrons arranged as 2, 8, 8.

- Identify the group number

Locate each element in the periodic table to find the group number. Magnesium (Mg) is in group 2, chlorine (Cl) is in group 17, beryllium (Be) is in group 2, and argon (Ar) is in group 18.

Key concepts

Atomic Number

The atomic number of an element is a fundamental property that tells us the number of protons in an atom's nucleus. For example, magnesium has an atomic number of 12. This means every magnesium atom has 12 protons in its nucleus.
The atomic number also determines the element's identity and its position on the periodic table.

• Atomic number = number of protons
• Defines the element
• Determines position on the periodic table

Knowing the atomic number is crucial to understanding other properties of the element, like its electron configuration.

Periodic Table

The periodic table organizes elements in a way that showcases their similarities and trends. It is organized in rows and columns based on their atomic number.
Each row is called a period, and each column is called a group.

• Rows = Periods
• Columns = Groups
• Elements are ordered by increasing atomic number

The table also shows how elements with similar properties are aligned vertically, making it clearer to see patterns in reactivity and other chemical properties. This arrangement helps in easily finding the atomic number and group number for any element.

Group Number

The group number of an element is found at the top of each column in the periodic table. Elements in the same group have similar chemical properties.
For example, magnesium and beryllium are both in group 2 and share similar properties because they have the same outer shell electron configuration.

• Magnesium (Mg) in group 2
• Chlorine (Cl) in group 17
• Beryllium (Be) in group 2
• Argon (Ar) in group 18

Group numbers are essential for predicting the behavior of an element in chemical reactions, as they indicate the number of electrons in the outermost shell.

Electron Configuration

The electron configuration describes how electrons are distributed in an atom's orbitals.
It follows a specific order, filling from the lowest energy level to the highest. For example, magnesium (with an atomic number of 12) has an electron configuration of 2, 8, 2. This means it has:

• 2 electrons in the first shell
• 8 electrons in the second shell
• 2 electrons in the third shell

Understanding electron configurations helps explain an element's placement in the periodic table and its chemical properties. Each shell can hold a certain number of electrons, influencing how elements bond and interact.