IB DP Chemistry S 2.4 From models to materials IB Style Question Bank SL Paper 1

Markscheme: A

1. Absorption Spectrum (Spectrum A):

   • When light passes through a cold gas cloud, certain wavelengths of light are absorbed by the atoms or molecules in the gas.
   • These absorptions occur at specific, discrete wavelengths, creating dark lines or bands in the spectrum. These dark lines represent the energy levels of the atoms or molecules in the gas cloud.
   • The absorbed wavelengths are characteristic of the elements present in the gas, and by analyzing the absorption spectrum, scientists can identify the composition of the gas.

2. Emission Spectrum (Spectrum B):

   • When a gas cloud is hot, the atoms or molecules in the gas can gain energy.
   • As these excited atoms or molecules return to lower energy states, they release the excess energy in the form of light.
   • The emitted light consists of specific, discrete wavelengths, producing bright lines or bands in the spectrum. These lines are characteristic of the elements in the gas cloud.
   • By studying the emission spectrum, scientists can identify the elements present and gain information about the temperature and density of the gas.

In summary:

• Absorption Spectrum (Spectrum A): Dark lines due to absorption of specific wavelengths by the cold gas.
• Emission Spectrum (Spectrum B): Bright lines due to the emission of specific wavelengths by the hot gas.