Background to Atomic Structure Flashcards
(13 cards)
What was the accepted view of the atomic structure in 1806?
Daltons theory of atomic structure stated:
- Each element is composed of atoms.
- Atoms of a given element are all of same type
- Atoms of different elements are different.
- Atoms do not change into different atoms throughout a reaction
- Compounds are formed when atoms of two or more elements combine.
What did J.J. Thompson discover in 1897?
J.J Thompson was credited with discovering the electron when he determined the mass to charge ratio of electrons by his “cathode ray tube” experiments.
The experiments showed that electrons are a common constituent of all matter.
What did Millikan discover in 1909?
In 1909, Millikan carried out his famous oil-drop experiment and determined the charge of an electron.
What was known of the atom in 1910?
- The diameter of an atom was known to me 10<span>-10</span><span> </span>m (1 Å). The masses and charges were also known:
- Electron - single negative charge and a mass of 1/1836 atomic mass units (AMU).
- Proton - single positive charge and a mass of 1 AMU
- Neutron - zero charges and a mass of 1 AMU.
What experiment did Rutherford, Geiger and Marsden conduct in 1910?
- Fired alpha particles at thin foils of elements and looked at how they were scattered.
- They proposed that if all positive charge was concentrated in a smaller volume in the centre of the atom, this would create an electric field.
- The electric field is large enough to repel the alpha particle and to scatter it at a much larger angle.
What information was derived from Rutherford’s experiment?
- Most mass of the atom is in the central nucleus.
- Electrons surround the nucleus
- Elements are described by atomic mass, A, and their atomic number, Z.
- The periodic table orders elements by increase atomic number, Z.
What is electromagnetic radiation?
Electromagnetic radiation is made up of oscillating perpendicular magnetic and electric fields travelling through space at speed c = 3.0 x 108 ms -1
We can describe electromagnetic radiation by speed, c, frequency, v, and wavelength λ.
What is black body radiation?
- Black bodies are objects that emit or absorb energy at any wavelength.
- When objects are heated to a high enough temperature, they begin to emit visible light.
- As temperature increases, the frequency of emitted light increases to a point.
- Classical physics fails to explain the relationship between the temperature of the object and frequency of light emitted.
What did Max Planck find in 1900?
- Found that he could explain the relationship between blackbody radiation if the electromagnetic radiation could only have certain energies.
- Referred to as quantisation of energy.
- The energy of electromagnetic radiation is E = hv
- E is energy, in J, h = Planck’s constant (6.626 x 10-34 J s) and v is the frequency in s-1
What is the photoelectric effect?
- When the light of a certain frequency strikes a metal surface, electrons are ejected from the metal.
- The velocity of the ejected electrons depends on the frequency of light, not intensity.
- This is the opposite of what classical physics would state, which would state that velocity depends on the intensity.
- Electrons are only emitted if the frequency is above the threshold
What did Einstein suggest in 1905?
- Einstein suggested that light - electromagnetic radiation - was made up of particles known as “photons” of energy.
- E = hv
- The electrons emitted from the metal have kinetic energy Ek
- Ek = 1/2 (mev2) = hv - φ
What is Bohr’s Model?
Bohr’s model went against the accepted classical physics and suggested that an electron could move around the nucleus in certain circular stable orbits w/out emitting radiation.
Radiation would only be emitted as the electron moved between these orbits.
