The identity of any chemical element is fundamentally determined by the number of protons residing in its nucleus. This count is known as the atomic number, which serves as the unique fingerprint for every element on the periodic table. The atomic number organizes the elements sequentially, starting with hydrogen (atomic number 1). For an atom to be electrically neutral, the positive charge of its protons must be exactly balanced by the negative charge of its electrons.
Linking Electron Count to Element Identity
The atomic number (\(Z\)) is defined as the total count of protons found within an atom’s nucleus. In a neutral atom, the number of electrons must precisely match the number of protons to maintain a zero net electrical charge. Therefore, an atom possessing 35 electrons must also contain 35 protons in its nucleus.
This proton count of 35 corresponds directly to the atomic number \(Z=35\). Consulting the periodic table confirms that element 35 is Bromine (\(\text{Br}\)). If the electron count deviates from 35, the substance is no longer a neutral atom but an ion, such as the bromide ion (\(\text{Br}^-\)).
The Element with 35 Electrons: Bromine
The element Bromine (\(\text{Br}\)) is a nonmetal belonging to Group 17 of the periodic table, commonly known as the halogens. It is one of only two elements that exist as a liquid at standard room temperature and pressure, alongside mercury. Bromine presents as a dense, volatile liquid with a distinctive red-brown color and a strong, pungent odor. Its name is derived from the ancient Greek word bromos, meaning “stench.”
Bromine and its compounds are utilized across several industries.
- A major modern application is in the form of brominated compounds used as flame retardants in materials like plastics, textiles, and electronics.
- It is used in agricultural chemicals, such as pesticides and soil fumigants.
- Its derivatives are important intermediates in the synthesis of various pharmaceuticals and dyes.
- It serves as a disinfectant in water purification, often as an alternative to chlorine in pools and hot tubs.
Electron Arrangement and Chemical Behavior
The chemical behavior of Bromine is a direct consequence of the arrangement of its 35 electrons across different energy levels or shells. The shell structure for a neutral Bromine atom is 2, 8, 18, 7, meaning the outermost shell contains 7 electrons.
These seven outermost electrons are known as valence electrons, and they are responsible for nearly all of Bromine’s chemical interactions. Because the valence shell is one electron short of the stable configuration of eight electrons (an octet), Bromine exhibits a high tendency to gain a single electron. This strong drive makes Bromine a highly reactive element, characteristic of the Group 17 halogen family. When Bromine gains an electron, it forms the stable bromide ion (\(\text{Br}^-\)), achieving the same electron configuration as the noble gas Krypton.