Question

Write Lewis dot symbols for the following ions: (a) \(\mathrm{Li}^{+}\), (b) \(\mathrm{Cl}^{-}\) (c) \(\mathrm{S}^{2-}\) (d) \(\mathrm{Sr}^{2+}\) (e) \(\mathrm{N}^{3-}\).

Short answer

\( \mathrm{Li}^{+} \) has no dots; \( \mathrm{Cl}^{-} \), \( \mathrm{S}^{2-} \), and \( \mathrm{N}^{3-} \) have eight dots; \( \mathrm{Sr}^{2+} \) has no dots.

Step-by-step solution

Understanding Lewis Dot Symbols

Lewis dot symbols represent the valence electrons of atoms and ions as dots around the symbol of the element. Each dot represents one valence electron. For ions, we need to consider the loss or gain of electrons corresponding to their charge.

Example (a): Writing Lewis Dot Symbol for \( \mathrm{Li}^{+} \)

Lithium has one valence electron in its neutral state. As a \( \mathrm{Li}^{+} \) ion, it has lost one electron, resulting in no electrons to show. Therefore, the Lewis dot symbol for \( \mathrm{Li}^{+} \) is simply Li with no dots: \( \text{Li}^+ \).

Example (b): Writing Lewis Dot Symbol for \( \mathrm{Cl}^{-} \)

Chlorine has seven valence electrons in its neutral state. As a \( \mathrm{Cl}^{-} \) ion, it gains one electron to complete its octet. The Lewis dot symbol will have eight dots (an octet) around the symbol Cl: \( \text{:Cl:}^{-} \).

Example (c): Writing Lewis Dot Symbol for \( \mathrm{S}^{2-} \)

Sulfur has six valence electrons in its neutral state. As a \( \mathrm{S}^{2-} \) ion, it gains two electrons, making a total of eight valence electrons. The Lewis dot symbol will have eight dots around the symbol S: \( \text{:S:}^{2-} \).

Example (d): Writing Lewis Dot Symbol for \( \mathrm{Sr}^{2+} \)

Strontium in its neutral state has two valence electrons. As a \( \mathrm{Sr}^{2+} \) ion, it loses both these electrons. Therefore, the Lewis dot symbol is just Sr with no dots: \( \text{Sr}^{2+} \).

Example (e): Writing Lewis Dot Symbol for \( \mathrm{N}^{3-} \)

Nitrogen has five valence electrons in its neutral state. As a \( \mathrm{N}^{3-} \) ion, it gains three electrons, making the total number of valence electrons eight. The Lewis dot symbol for \( \mathrm{N}^{3-} \) will have eight dots: \( \text{:N:}^{3-} \).

Key concepts

Valence Electrons

Valence electrons are the outermost electrons in an atom and play a crucial role in chemical bonding. These electrons are located in the highest energy level of an atom and are the easiest to remove or share during chemical reactions.
The number of valence electrons determines an atom's reactivity and the types of bonds it can form.

• In the periodic table, elements in the same group have the same number of valence electrons.
• For atoms, the number of valence electrons can be predicted by their group number in the periodic table.
• For example, lithium (Li) is in group 1 and has 1 valence electron, so in its ionized form (\( ext{Li}^+ \) ), it loses this electron.

Understanding valence electrons is key to drawing Lewis dot symbols, as these diagrams focus on representing the valence electrons.

Ionic Charge

Ionic charge refers to the electrical charge that an atom acquires when it loses or gains electrons. Atoms strive for a full valence shell, often achieving this by becoming ions.
By losing or gaining electrons, atoms transform into positively or negatively charged ions.

• Positive ions, or cations, form when an atom loses electrons, decreasing their overall negative charge. For example, Sr in its neutral state has 2 valence electrons, and when it loses these electrons, it forms a Sr\(^{2+}\) ion.
• Negative ions, or anions, form when an atom gains electrons, increasing their negative charge; thus, Cl gains an electron to form Cl\(^-\).

To write Lewis dot symbols for ions, consider whether the ion has gained or lost electrons and adjust the number of dots accordingly

Electron Configuration

Electron configuration describes the distribution of electrons in an atom's atomic orbitals. Each atom has a unique electron configuration that influences its chemical properties and reactivity.
It follows a specific order based on energy levels and subshells, such as \(1s\), \(2s\), \(2p\), etc.

• The electron configuration of an atom can be determined using the periodic table; for instance, nitrogen’s neutral electron configuration is \(1s^2 2s^2 2p^3\).
• When an atom becomes an ion, its electron configuration changes. For example, when nitrogen becomes \( ext{N}^{3-} \), it gains 3 electrons, completing its outermost 2p orbitals with a total of \(2s^2 2p^6\).

The electron configuration helps to understand how atoms will interact with each other in chemical reactions.

Element Symbols

Element symbols are one or two-letter abbreviations that represent an element in the periodic table. They serve as a universal shorthand in chemistry.
The symbol is usually derived from the element’s name, either in English or in Latin.

• One-letter symbols, such as H for hydrogen and N for nitrogen, use a single uppercase letter.
• Two-letter symbols, like Na for sodium and Cl for chlorine, use one uppercase followed by a lowercase letter.
• Element symbols are central to writing chemical equations, creating compound formulas, and drawing Lewis structures.

Recognizing these symbols helps easily identify the elements being referenced, which is essential for drawing accurate Lewis dot structures.