Ch3: Arrangement of Electrons in the Atom Flashcards
(30 cards)
Where did Rutherford propose electrons were located? Why was this incorrect
-Electrons revolved around the nucleus
-incorrect because it is too simple, the electrons would spiral into the nucleus and the atom would collapse
Explain a continuous spectrum
When white light passes through a prism, it is broken up into a continuous array of colours
Explain an emission line spectrum
-Electric current passes through a hydrogen discharge tube and causes light to pass through a prism
-Series of narrow coloured lines were seen instead of a continuous spectrum
Distinguish between a spectroscope and spectrometer
-Spectrometer used to STUDY spectra
-Spectroscope used to OBSERVE spectra (cannot measure wavelengths of light)
What were Bohr’s observations? (loose explanation)
-Electrons revolve around the nucleus in fixed paths called orbits
-Orbits are also called energy levels
-Electrons normally occupy the ground state
-When the atom absorbs a specific amount of energy, the electrons to jump to a higher energy level (excited state)
-Electrons are unstable and fall back down to the lower energy level and release the excess energy as a photon of light.
-The frequency of the photon of light depends on the energy difference between the two energy levels (E2-E1=hf)
-Each frequency appears as a particular line of colour on the emission spectrum
What does the Emission Line Spectra provide?
It provides spectroscopic evidence for the existence of energy levels
What is an energy level?
A fixed energy value that an electron in an atom may have
-They were definite/quantised
-represented as n=___ (e.g. n=1)
What is the ground state of an atom?
Electrons occupy the lowest available energy levels
What is the excited state of an atom?
Electrons occupy higher energy levels than those available in the ground state
State and explain the 3 series in energy levels
-Lyman: Electrons fall back to n=1, ultra-violet region
-Balmer: Electrons fall back to n=2, visible region
-Paschen: Electrons fall back to n=3. infrared region
Little Black Purse
Lyman Balmer Paschen
What is the standard answer to Bohr’s Theory?
- Electrons are restricted to energy levels where they have quantised energy
- Electrons occupy the ground state
- If a fixed amount of energy is absorbed, electrons jump to a higher energy level and are now in the excited state
- The electrons are unstable in this state and fall back down to a lower energy level and emit a photon of light, of a specific frequency
- This frequency is calculated using E2-E1=hf, where.. (Explain each figure)
- Each element has a different distribution of energy levels which give rise to different electronic transitions and unique emission spectrum
What is Atomic Absorption Spectrometry (AAS) ?
It is an analytical technique used to measure the concentration of elements
How does AAS work?
-White light is passed through a gaseous sample and into a prism
-The atoms of different elements in the sample absorb characteristic wavelengths of light
-The wavelengths absorbed are absent from the spectrum
How does the absorption spectrum and emission spectrum correlate?
-They are photographic negatives of each other.
-This is because atoms in the ground state absorb the same amount of energy they emit in the excited state
What are the uses of AAS?
-Water analysis for heavy metals, e.g. Lead (Pb), Cadmium (Cd), Mercury (Hg)
-Blood analysis for toxic metals, e.g. Lead (Pb)
-Forensics for gunshot residue, e.g. Lead (Pb), Barium (Ba), Antimony (Sb)
What is a sublevel?
a subdivision of a main energy level and consists of one or more orbitals of the same energy
What evidence was suggested for the existence of sublevels?
The single lines on the emission spectra was actually a number of lines very close together
Other information about an energy sublevel
-All main energy levels, except the first, is made up of a number of sublevels close in energy
-The number of sublevels in an energy level is the value of a main energy level (n=4 has 4 sublevels)
-Named as s,p,d,f and increase in energy from s to f
What is wave-particle duality and who suggested it?
-Louis De Broglie
-He suggested that all moving particles had a wave motion associated with them
-It is the concept that electrons behave like waves and like particles
What is Heisenberg’s Uncertainty Principle?
States that it is impossible to measure at the same time both the velocity and the position of an electron
What is the reasoning behind Heisenberg’s Uncertainty Principle?
-If a beam of light is used to detect an electron, the beam strikes the electron and determines its position
-However, since the mass of an electron is so tiny, the beam of light immediately changes the velocity/speed of the electron
What were the Limitations of Bohr’s Theory?
-Theory works for hydrogen, but not for atoms with more electrons
-Wave-particle duality
-Heisenberg’s Uncertainty Principle
-Sublevels
What is an orbital?
A region in space within which there is a high probability (95%) of finding an electron
What did Erwin Schrodinger do?
He devised mathematical equations to work out the probability of finding an electron in any particular sublevel in an atom
-He found the shapes of the 4 types of orbitals (s,p,d,f)
