Question

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

Short answer

Hydrogen has 1 valence electron; bromine has 7 valence electrons.

Step-by-step solution

Understanding Valence Electrons

Valence electrons are the electrons present in the outermost shell of an atom. These electrons are important because they are involved in bonding with other atoms.

Identifying Hydrogen's Electron Configuration

Hydrogen has an atomic number of 1, which means it has 1 electron. This electron is located in the first and outer shell, making it the valence electron. Therefore, hydrogen has 1 valence electron.

Identifying Bromine's Electron Configuration

Bromine has an atomic number of 35. The electron configuration is \[ 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^5 \]. The outermost shell for bromine is the 4th shell, which contains the electrons from the subshells 4s and 4p. The total number of valence electrons is the sum of electrons in these subshells: \[ 4s^2 + 4p^5 = 7 \]. Therefore, bromine has 7 valence electrons.

Key concepts

Electron Configuration

Electron configuration is a way of understanding how electrons are distributed in an atom. Electrons fill the orbitals, or energy levels, in a specific order based on the principles of quantum mechanics. This arrangement helps us understand the chemistry and bonding behavior of an atom.

• Electrons fill from lower to higher energy levels. Starting with the 1s orbital, they move to 2s, 2p, and so forth.
• Each orbital can hold a certain number of electrons; for example, s orbitals can hold 2, while p orbitals can hold up to 6.
• Knowing the configuration allows us to determine valence electrons, which are crucial for predicting how an atom interacts in chemical reactions.

For example, the electron configuration of oxygen is \(1s^2\, 2s^2\, 2p^4\), indicating it has 6 valence electrons in its outer shell. This ability to label and visualize the electron arrangement in atoms sets the stage for understanding concepts like bonding, molecular geometry, and more.

Hydrogen Atom

Hydrogen is unique because it's the simplest and lightest atom. It has an atomic number of 1, which means there is just one proton in the nucleus accompanied by one electron outside it. This single electron stays in the lowest energy level, the 1s orbital, making the electron configuration very straightforward: \(1s^1\).
Due to this simple structure:

• Hydrogen has 1 valence electron, which can easily interact with other elements to form bonds. This makes hydrogen quite reactive, despite its simplicity.
• Hydrogen can form covalent bonds, where it shares its valence electron with another atom to create a molecule, like in water (H₂O).
• Hydrogen is also capable of losing its single electron to form a positive ion, known as a proton, which plays a significant role in acid-base chemistry.

These characteristics of hydrogen make it foundational in the study of chemistry and essential in numerous chemical processes.

Bromine Atom

Bromine is a heavier and more complex atom compared to hydrogen. With an atomic number of 35, bromine's electrons fill several energy levels. Understanding its electron configuration helps us see why bromine behaves the way it does chemically. The electron configuration for bromine is \[1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^2\, 3d^{10}\, 4p^5\].

• Focus on the 4th energy level, which is the outermost for bromine. It contains the electrons in the 4s and 4p orbitals.
• The 4s orbital holds 2 electrons, and the 4p orbital has 5, making a total of 7 valence electrons.
• Having 7 valence electrons makes bromine highly reactive, often seeking to gain an electron to achieve a stable octet configuration. This desire influences its reactivity and places bromine within the halogen group on the periodic table.

Bromine's chemistry, with its ability to readily form compounds, is integral to both organic and inorganic chemical reactions, emphasizing why understanding its electron configuration is so beneficial.