Question

State the number of valence electrons for a hydrogen atom and a bromine atom in a covalent bond.

Short answer

Hydrogen has 1 valence electron, and bromine has 7 valence electrons.

Step-by-step solution

- Determine Valence Electrons for Hydrogen

The hydrogen atom is in Group 1 of the periodic table, which means it has one valence electron. Valence electrons are those electrons located in the outermost shell of an atom.

- Determine Valence Electrons for Bromine

Bromine is located in Group 17 of the periodic table, which means it has seven valence electrons. These are the electrons in the outermost shell of the bromine atom and are available for bonding.

- Sum of Valence Electrons in Covalent Bond

In a covalent bond, both hydrogen and bromine share their valence electrons to achieve greater stability. Since hydrogen has 1 and bromine has 7 valence electrons, together they contribute 8 valence electrons to the covalent bond.

Key concepts

Covalent Bond

When atoms form a covalent bond, they share electrons. This type of bond typically forms between nonmetals, like hydrogen and bromine. The electrons are shared to meet each atom's need for a full valence shell—usually eight electrons for elements of higher atomic numbers such as bromine (often referred to as the octet rule). In our case:

• Hydrogen, with its one valence electron, shares with bromine's seven valence electrons.
• Together, they create a stable molecule through shared electron pairs.

Understanding covalent bonds is crucial because they are fundamental to many chemical processes. The shared system not only holds the molecule together but also contributes to the fulfillment of each atom's desire for stability. This shared electron system is what creates the molecule's structure, and can vary in the number of shared electrons, producing single, double, or even triple bonds. In our example with hydrogen and bromine, a single pair (one electron from each) is shared to form a single covalent bond.

Periodic Table

The periodic table is a chemical map of the elements, organizing them by increasing atomic number. Every element is grouped by similar chemical properties, based on the number of valence electrons in the outermost shell. The importance of the periodic table in understanding covalent bonds cannot be overstated:

• Hydrogen belongs to Group 1. It has a single valence electron, making it highly reactive and capable of forming bonds with most other atoms.
• Bromine is in Group 17, known as the halogens, which naturally have seven valence electrons and are one electron short of a full shell.

Placing elements in specific groups helps predict how they might interact. This predictive ability is a powerful tool for chemists. Thus, knowing the position of an element on the periodic table allows scientists to infer its reactivity and the type of bonds it might form.

Chemical Stability

Chemical stability refers to an atom's general resistance to change in energy and reactivity when its outer shell is full. For most atoms, achieving a full outer electron shell is synonymous with achieving stability. In covalent bonds, stability is reached:

• By sharing electrons, atoms achieve a stable outer shell configuration.
• For hydrogen, reaching a configuration similar to helium provides stability.
• For bromine, sharing with hydrogen helps it attain the complete "octet."

These shared electrons stabilize the respective atoms, minimizing potential energy differences. Atoms are always striving toward a lower energy state, hence why gaining or sharing electrons to fill the valence shell is energetically favorable. This concept lays at the foundation of why molecules form, exist, and how they behave in chemical reactions. So, this intimate relationship between electron sharing and stability is fundamental to understanding chemical interactions.