Problem 1 - General Chemistry: Principles and Modern Applications

Question

Write Lewis symbols for the following atoms. (a) \(\mathrm{Kr}\); (b) Ge; (c) \(\mathrm{N} ;\) (d) Ga; (e) As; (f) Rb.

Step-by-Step Solution

Answer

(a) \(\mathrm{Kr}: . . . . . . . .\) (eight dots evenly spread and paired around Kr symbol). (b) \(\mathrm{Ge}: . . . .\) (four dots around Ge symbol forming a square). (c) \(\mathrm{N}: . . . . .\) (three paired and two unpaired dots around N). (d) \(\mathrm{Ga}: . . .\) (three unpaired dots around Ga). (e) \(\mathrm{As}: . . . . . \) (three paired and two unpaired dots around As). (f) \(\mathrm{Rb}: .\) (one dot next to Rb).

Step 1: Understand Lewis Symbols

Lewis symbols or Lewis dot diagrams are diagrams that show the bonding between atoms of a molecule, and the lone pairs of electrons that may exist in the molecule. Each dot represents a valence electron, each line represents a bonded pair of electrons and each pair of dots or line represents a single electron pair.

Step 2: Identify atomic numbers

Identify the atomic numbers respective to given atoms. (a) Kr (krypton) has an atomic number of 36. (b) Ge (germanium) has an atomic number of 32. (c) N (nitrogen) has an atomic number of 7. (d) Ga (gallium) has an atomic number of 31. (e) As (arsenic) has an atomic number of 33. (f) Rb (rubidium) has an atomic number of 37.

Step 3: Identify number of valence electrons

Based on atomic number determine the number of valence electrons. Kr has 8, Ge has 4, N has 5, Ga has 3, As has 5, and Rb has 1 valence electron.

Step 4: Draw Lewis symbols

Draw Lewis symbols. Since each dot represents a valence electron, draw corresponding dots around the element's symbol to represent its valence electrons. Arrange the first four dots around the symbol to denote one electron in each of the four sides (up, right, down, left), then start pairing until the number of dots equal the number of valence electrons for that atom.

Key Concepts

Valence Electrons

Valence electrons are the outermost electrons of an atom that participate in chemical bonding. They play a vital role in determining the chemical properties of an element. Understanding valence electrons helps us predict how atoms will bond with each other. For example, elements in the same group of the periodic table have the same number of valence electrons, which gives them similar chemical properties.

These electrons are represented as dots around the symbol of an element in Lewis dot diagrams. This helps visualize how atoms bond in a molecule. The more valence electrons an atom has, the more an atom is likely to form stable bonds with other atoms. Let's illustrate this with a few examples:

• Krypton (Kr), found in group 18, has 8 valence electrons, making it very stable.
• Germanium (Ge), located in group 14, has 4 valence electrons and can make up to 4 bonds.
• Nitrogen (N), part of group 15, possesses 5 valence electrons, usually making 3 bonds to complete its octet.

Each case showcases how valence electrons guide the formation of molecules.

Atomic Numbers

The atomic number of an element tells us the number of protons in its nucleus. This number is unique for each element and defines the identity of the element in the periodic table. Additionally, in a neutral atom, the atomic number gives the total number of electrons, providing insights into its electronic configuration.

To determine the number of valence electrons, knowledge of the atomic numbers is essential. Here are some examples from the exercise:

• Krypton (Kr) has an atomic number of 36, placing it in group 18 with 8 valence electrons.
• Germanium (Ge) has an atomic number of 32, positioning it in group 14 with 4 valence electrons.
• Rubidium (Rb), with an atomic number of 37, belongs to group 1 with just 1 valence electron.

Understanding atomic numbers allows us to predict how an element will react chemically and helps in drawing accurate Lewis symbols.

Electron Pairs

Electron pairs consist of two electrons occupying the same orbital or bond and can either be bonding pairs or lone pairs. When atoms form a chemical bond, their valence electrons pair up, either as shared pairs (covalent bonds) or as lone pairs remaining on individual atoms.

Lewis symbols are particularly useful in showing how electron pairs are formed around atoms. Each pair of dots or lines between symbols represents these electron pairs. For instance, the steps to illustrate the electron pairs include:

• Placing the initial four dots around the atom symbol, each dot representing one electron on each side.
• Pairing up the electrons as needed until the number of dots equals the number of valence electrons.

This gives a visual depiction of how bonds form and helps identify the presence of lone pairs, which are significant in determining the shape and reactivity of molecules.