Question

Draw the electron dot formula for each of the following elements: (a) He (b) \(\mathrm{Pb}\) (c) Se (d) Ne (e) \(\mathrm{Cs}\) (f) Ga (g) Sb (h) Br

Short answer

He: ∶He, Pb: ∶Pb:, Se: ∶Se:, Ne: ∶Ne:, Cs: Cs∶, Ga: Ga:, Sb: ∶Sb:, Br: ∶Br:

Step-by-step solution

Understand Electron Dot Notation

Electron dot formulas, or Lewis dot structures, represent an element's valence electrons as dots around the symbol of the element. Each dot stands for one valence electron. We will determine the number of valence electrons for each element to draw their electron dot formula.

Determine Valence Electrons for Each Element

Identify the group number for each element in the periodic table to find the number of valence electrons. - Helium (He) is in Group 18 with 2 valence electrons. - Lead (Pb) is in Group 14 with 4 valence electrons. - Selenium (Se) is in Group 16 with 6 valence electrons. - Neon (Ne) is in Group 18 with 8 valence electrons. - Cesium (Cs) is in Group 1 with 1 valence electron. - Gallium (Ga) is in Group 13 with 3 valence electrons. - Antimony (Sb) is in Group 15 with 5 valence electrons. - Bromine (Br) is in Group 17 with 7 valence electrons.

Draw the Electron Dot Formula for Each Element

Use the number of valence electrons determined in Step 2 to place dots around the symbol for each element: - (a) 2 dots for He: ∶He - (b) 4 dots for Pb: ∶Pb: - (c) 6 dots for Se: ∶Se: - (d) 8 dots for Ne: ∶Ne: - (e) 1 dot for Cs: Cs ∶ - (f) 3 dots for Ga: Ga: - (g) 5 dots for Sb: ∶Sb: - (h) 7 dots for Br: ∶Br:

Key concepts

Valence Electrons

Valence electrons are the outermost electrons of an atom and play a crucial role in chemical bonding. Because these electrons are on the outer shell, they are the ones involved in forming bonds with other atoms. Valence electrons determine an element's chemical properties. To find the number of valence electrons, you often look at the group number of the element in the periodic table.
For instance, helium (He), being in Group 18, has 2 valence electrons, even though elements in Group 18 usually have 8 valence electrons. This exception is because helium is a noble gas with only one shell. Lead (Pb) in Group 14 has 4 valence electrons, while bromine (Br) in Group 17 has 7 valence electrons. Each of these elements, given their unique number of valence electrons, will form bonds to achieve a stable electronic arrangement often similar to the nearest noble gas.

Periodic Table Groups

The periodic table is divided into columns known as groups. Each group contains elements that share similar characteristics and, often, the same number of valence electrons. This is because the elements in a group have the same or similar outer electron configurations.

• Group 1, also known as the alkali metals, has elements like cesium (Cs) with a single valence electron.
• Group 14 contains elements like lead (Pb) with 4 valence electrons.
• Group 16, also known as the chalcogens, includes selenium (Se) which has 6 valence electrons.
• Group 18, known as the noble gases, includes helium (He) and neon (Ne), which are characterized by a complete outer shell.

Understanding the group of an element helps predict its chemical behavior and the types of reactions it will undergo.

Lewis Structures

Lewis structures, also known as electron dot structures, are diagrams that represent the valence electrons of an atom as dots around the element's symbol. These structures help visualize the molecular structure and the arrangement of electrons, allowing us to predict bonding patterns and molecular shapes.
When drawing a Lewis structure:

• Each dot represents one valence electron.
• Dots are placed one by one around the symbol, starting from any position and moving clockwise, pairing up as needed.
• For example, with 4 valence electrons, as seen with lead (Pb), you would have dots on all four sides of the symbol: :Pb:.
• With 8 valence electrons, such as in neon (Ne), the goal is to have dots completely surround the symbol, indicating a full stable outer shell: ∶Ne:.

Lewis structures are essential tools for understanding how molecules form and predict how they interact in chemical reactions.