Problem 1 - Chemical Principles in the Laboratory

Question

First you need to find the number of valence electrons in \(\mathrm{NHCl}_{2}\). For counting purposes with Lewis structures, the number of valence electrons in an atom of a main group clement is equal to the last digit in the group number of that clement in the periodic table. \(\mathrm{N}\) is in Group __________ H is in Group __________ Cl is in Group __________ In \(NHCl_{2}\)there is a total of __________ valence electrons.

Step-by-Step Solution

Answer

NHCl2 has 20 valence electrons.

Step 1: Identifying the Periodic Table Groups

First, identify the group numbers for each element in the periodic table. Nitrogen (N) is in Group 15, Hydrogen (H) is in Group 1, and Chlorine (Cl) is in Group 17.

Step 2: Counting Nitrogen Valence Electrons

Since nitrogen is in Group 15, it has 5 valence electrons (15 minus 10, or simply use the last digit, 5).

Step 3: Counting Hydrogen Valence Electrons

Hydrogen, being in Group 1, has 1 valence electron.

Step 4: Counting Chlorine Valence Electrons

Chlorine, in Group 17, has 7 valence electrons (17 minus 10, or use the last digit, 7).

Step 5: Adding Up Total Valence Electrons

Now, add the valence electrons. NHCl2 has one nitrogen atom, one hydrogen atom, and two chlorine atoms: \[5 ( ext{from } N) + 1 ( ext{from } H) + 2 \times 7 ( ext{from } Cl) = 5 + 1 + 14 = 20\] Thus, the total number of valence electrons in \(NHCl_2\) is 20.

Key Concepts

Lewis structures

Lewis structures allow us to visualize the arrangement of atoms and the distribution of electrons within a molecule. These diagrams are helpful when it comes to understanding the bonding between atoms. Each dot in a Lewis structure represents a valence electron.
For example, by representing nitrogen, hydrogen, and chlorine, you can see how the electrons are shared or transferred between these atoms in a molecule like \( NHCl_2 \). Not only do these structures show single, double, or triple bonds by the number of lines between atoms, but they also help predict the shape and reactivity of the molecule.

• Each atom is typically surrounded by dots representing its valence electrons.
• The goal is to fulfill the octet rule, where atoms bond in such a way so they attain eight electrons in their valence shell.
• Exceptions occur for hydrogen which is stable with two valence electrons.

Understanding these structures helps us in calculating properties like molecular shape and polarity, making them essential tools in chemistry.

periodic table groups

The periodic table is arranged in a way that elements are grouped based on their similar properties. Each column is a group, and elements within a group often share the same number of valence electrons.
Nitrogen is in Group 15, indicating that it has 5 valence electrons, as the group's last digit signifies the number of valence electrons for main-group elements. This pattern, however, repeats until Group 18.

• Group 1: Typically contains alkali metals; they have 1 valence electron.
• Group 17: Known as halogens; they possess 7 valence electrons.
• Group 18: Known for noble gases with a full valence shell of 8 electrons.

Understanding these group numbers is crucial. It allows scientists and students to predict the chemical behavior of elements, such as how they bond or react, with greater accuracy.

molecular composition

Molecular composition refers to the types and numbers of atoms present in a molecule. By using the formula \( NHCl_2 \) as an example, we can deduce the molecule’s composition has one nitrogen atom, one hydrogen atom, and two chlorine atoms. This composition is key to determining the structure and properties of the molecule.
Understanding a molecule's composition is foundational for exploring:

• How atoms are arranged and connected, influencing molecular geometry.
• Types of bonds that form and their respective strengths.
• Molecule's chemical behavior and interactions with other substances.

By combining this with Lewis structures and periodic table insights, one can predict not only the molecular structure but also how a molecule might participate in complex reactions.