Question

Write the Lewis structure for each of the following atoms. a. He \((Z=2)\) b. Br \((Z=35)\) c. \(\operatorname{Sr}(Z=38)\) d. Ne \((Z=10)\) e. I \((Z=53)\) f. \(\operatorname{Ra}(Z=88)\)

Short answer

a. He Lewis structure: \(\mathrm{:He:}\) b. Br Lewis structure: \(\mathrm{.Br:}\) c. Sr Lewis structure: \(\mathrm{.Sr}\) d. Ne Lewis structure: \(\mathrm{:Ne:}\) e. I Lewis structure: \(\mathrm{.I:}\) f. Ra Lewis structure: \(\mathrm{.Ra}\)

Step-by-step solution

Finding the valence electrons for each atom

Use the atomic number (Z) to determine the number of protons in each atom and use the periodic table to find the group number. The group number corresponds to the number of valence electrons in each atom. a. He \((Z=2)\): Group 18 (Noble gases), 2 valence electrons. b. Br \((Z=35)\): Group 17 (Halogens), 7 valence electrons. c. \(\operatorname{Sr}(Z=38)\): Group 2 (Alkaline earth metals), 2 valence electrons. d. Ne \((Z=10)\): Group 18 (Noble gases), 8 valence electrons. e. I \((Z=53)\): Group 17 (Halogens), 7 valence electrons. f. \(\operatorname{Ra}(Z=88)\): Group 2 (Alkaline earth metals), 2 valence electrons.

Drawing the Lewis structures for each atom

Draw the element symbol and place dots representing the valence electrons around the symbol. For elements not in group 18, distribute the valence electrons with a maximum of two electrons in each direction until all valence electrons are placed. a. He: He is in Group 18 with 2 valence electrons. Its Lewis structure is: \[\mathrm{:He:}\] b. Br: Br is in Group 17 with 7 valence electrons. Its Lewis structure is: \[\mathrm{.Br:}\] c. Sr: Sr is in Group 2 with 2 valence electrons. Its Lewis structure is: \[\mathrm{.Sr}\] d. Ne: Ne is in Group 18 with 8 valence electrons. Its Lewis structure is: \[\mathrm{:Ne:}\] e. I: I is in Group 17 with 7 valence electrons. Its Lewis structure is: \[\mathrm{.I:}\] f. Ra: Ra is in Group 2 with 2 valence electrons. Its Lewis structure is: \[\mathrm{.Ra}\]

Key concepts

Valence Electrons

Valence electrons are the electrons located in the outermost shell of an atom, which can be involved in forming chemical bonds with other atoms. These electrons play a critical role in determining an atom's chemical properties and its ability to interact with other atoms.

For example, elements in the same group of the periodic table typically have the same number of valence electrons, which is why they often exhibit similar chemical behavior. For instance, helium (He), neon (Ne), and argon (Ar) are all noble gases with a full valence shell, contributing to their overall lack of reactivity.

To find the number of valence electrons in an atom, you can refer to the atom's group number for elements in Groups 1-2 and 13-18. These groups correspond directly to the number of valence electrons. For elements in Groups 3-12, which are transition metals, the determination of valence electrons is more complex due to their unique electron configurations.

Atomic Number

The atomic number, represented by the symbol (Z), is a fundamental property of an element and defines the number of protons in the nucleus of an atom. This number also determines the identity of the element: for example, hydrogen always has an atomic number of 1, while carbon always has an atomic number of 6.

The atomic number not only indicates the number of protons but also the number of electrons an atom has when it is neutral (no overall charge). Since the number of electrons equals the number of protons, the atomic number can be used to figure out the electron arrangement for a particular element. This arrangement includes the valence electrons, which dictate many of the element's chemical properties.

When working on exercises related to the Lewis structure, the atomic number is a key starting point as it enables students to quickly identify the number of valence electrons they need to represent around the symbol of the element.

Periodic Table

The periodic table is an essential tool for understanding the relationships between elements. It's arranged in such a way that elements with similar properties fall into the same columns, known as groups or families. Furthermore, the rows, called periods, indicate the number of shells an atom has.

The table is designed to highlight periodic trends, such as electronegativity, atomic radius, and ionization energy, which all change predictably across and down the table. These trends help in predicting how an element will behave in chemical reactions.

For drawing Lewis structures, the periodic table acts as a valuable reference to determine the number of valence electrons. By looking up the group number, you can easily find this information for most elements. The table also helps to understand why elements within the same group have similar Lewis structures due to their identical valence electron counts. In educational content, clarifying students' understanding of the periodic table can significantly aid in their mastery of depicting and comprehending Lewis structures.