Final answer:
The Bohr model describes the arrangement of electrons in the first 18 elements, where helium, neon, and argon of Group 18 have filled valence shells for stability, while others have partially filled shells and try to gain or lose electrons to stabilize. Initially successful for hydrogen, it fell short for larger atoms, paving the way for quantum mechanics.
Step-by-step explanation:
The Bohr model is a representation of atomic structures that illustrates how electrons are arranged in principal energy levels or shells around the nucleus. According to the Bohr model, the first 18 elements have electrons that fill these shells in a specific pattern. For example, the first shell can hold up to 2 electrons, while the second can contain up to 8 electrons.
Elements of Group 18, such as helium, neon, and argon, exhibit a full outer or valence shell. This full valence shell is known for being the most stable electron configuration. On the contrary, elements in other groups have partially filled valence shells, and they tend to gain or lose electrons to achieve stability, a concept crucial for understanding chemical bonding.
Historically, the Bohr model played a significant role as it marked the inception of early quantum theory with its explanation of the energy levels within the hydrogen atom. While successful in explaining hydrogen's emission spectrum, it failed to account for larger atoms, leading to the development of more advanced quantum mechanics. The distinct, fixed energy levels, or quantized orbits, proposed by Bohr are fundamental to the understanding of how absorption and emission spectra are formed.