Atomic Model/Mass Spectroscopy/Flame Tests/AAS

Name the 5 key contributors to the modern atomic model (in order)

John Dalton, J.J. Thomson, Ernest Rutherford, Niels Bohr, James Chadwick

What were John Dalton’s main contributions to atomic theory?

• All matter is composed of indivisible atoms

• Atoms of the same element are identical

What were J.J. Thomson’s main contributions to atomic theory?

• Discovered electrons using cathode ray tube

• Plum Pudding model - represents an atom as a positively charged sphere with negatively charged electrons embedded throughout

What was Ernest Rutherford’s main contribution to atomic theory?

• Gold foil experiment - discovery of the positively charged, small, dense nucleus in the centre of the atom, and surrounding orbiting electrons.

What was Niels Bohr’s main contribution to atomic theory

• Bohr Model - electrons in distinct energy levels/shells surrounding the nucleus, and can jump from one level to another, absorbing/emitting energy in the form of light

What were James Chadwick’s main contribution to atomic theory?

• Discovered the neutron, accounting for the existence of isotopes and the missing mass in atoms

• Completing the basic atomic structure

How did each model improve on the previous one?

Addressed limitations of previous models and incorporated new experimental evidence.

What atomic model do we use today?

The quantum mechanical model

Explain the Bohr model and how electrons move between energy levels.

Energy shells closest to the nucleus have the least energy and are the furthest apart

Electrons move between energy shells by emitting or absorbing energy in the form of light

What does a mass spectrometer do?

Measures the mass and abundance of isotopes in a sample of an element.

What are the 4 steps of a mass spectrometer?

Vaporisation/Ionisation, Acceleration, Deflection, Detection

How does vaporisation work in a mass spectrometer?

Solid/liquid samples are converted into gases in a vacuum chamber

How does ionisation work in a mass spectrometer?

Electrons are shot at the gas, knocking valence electrons off the atoms, leaving cations.

How does acceleration work in a mass spectrometer?

Cations are sped up by a electric field so they all have the same EK. Produces a high-speed ion beam directed towards the electromagnet.

How does deflection work?

• Electromagnet changes ion’s path based on mass and charge.

• The lighter and more charged an ion, the more its path is deflected.

• Ions of different masses and charges are directed toward different parts of the detector

How does detection work in a mass spectrometer?

Because of their differing paths, ions of each isotope are detected at a different part of the detector. It counts how many ions hit each part to calculate the abundance.

How do flame tests work?

A sample is placed over a flame and turns a specific colour. Energy from the flame excites the electrons, which absorb energy and jump to a higher shell. When they drop back down, they emit the previously absorbed energy in the form of visible light. Because different elements absorb/emit different amounts of energy, the colour of light produced is specific to that element.

How does atomic absorption spectroscopy work?

• Sample is vaporised to form free atoms

• A hollow cathode lamp emits a wavelength of light specific to the metal in the sample

• The atoms absorb the light

• The detector measures the decrease in light intensity (absorbance)

What is a calibration curve?

A graph showing the relationship between the absorbance of light and the concentration of metal in a sample.