Chapter 3 - Arrangement of Electrons in an Atom Flashcards
What happens to the continuous spectrum produced by a glass prism when the source of white light is replaced with light from a hydrogen discharge tube?
You only see a few colours with narrow lines and this spectrum is called an emission line spectrum
What is a discharge tube?
A glass tube filled with gas at low pressure, with an electric current passed through it
Spectrometer
Instrument used to carry out measurements on spectra
Spectroscope
Instrument used to simply observe spectra
Describe the experiment to carry out flame tests with various salts
- Using a damp wooden splint/platinum wire, hold a sample of salt in the blue flame of the Bunsen
- Repeat with the other salts
- Each metal gives a characteristic colour
- You can use the colours obtained to identify metals present in unknown compounds
What colour does lithium turn in the flame test?
Crimson
What colour does potassium turn in the flame test?
Lilac
What colour does barium turn in the flame test?
Green
What colour does copper turn in the flame test?
Blue-green
What colour does strontium turn in the flame test?
Red
What colour does sodium turn in the flame test?
Yellow
Summarise Bohr’s Theory of electrons (12)
- Electrons revolve around nucleus in fixed orbit
- Each energy level has a fixed amount of energy
- Energy levels are represented as n=1, n=2 etc
- Once an electron remains in one orbit/energy level it neither gains nor loses energy
- Atoms normally exist in their ground state
- When an atom in ground state is provided with energy, a specific amount of this energy is absorbed and the electrons from lower to higher energy levels
- Energy absorbed = difference in energy between ground and excited state
- Electrons in ground state are unstable and soon fall down to lower energy level, and this excess energy is released in the form of a photon of light
- Frequency of light emitted depends on the difference in energy between the two levels (E₂ - E₁ = hf)
- Energy difference between levels is proportional to frequency of light emitted
- Light of definite frequency appears as a line of particular colour on the emission line spectrum
- Each element has a unique emission line spectrum
Energy level
The fixed energy value that an electron in an atom may have
Ground state
Where electrons of an atom occupy the lowest available energy levels
Excited state
Where electrons of an atom occupy higher energy levels that those available in the ground state
Why does each element have a different emission line spectrum?
Each element has a different number of electrons and its own arrangement of these electrons in energy levels (and depending on how much energy is supplied). As electrons fall different distances, different frequencies of light are given off
What are the three series of light
Lymen series → invisible: found in ultraviolet radiation
Balmer series → Visible light
Paschen series → Invisible: infrared
What is an atomic absorption spectrum?
Atoms can absorb light. If white light is passed through a gaseous sample of an element, we see that the light that emerges has certain wavelengths missing. This is called the atomic absorption spectrum
Atomic absorption spectrometer
Instrument used in the analysis of water for heavy metals
What does s, p, d and f stand for in terms of energy sublevels?
sharp
principal
diffuse
fundamental
What did Louis de Broglie do?
Said you could detect the wave motion for an electron as it is such a small object
Heisenburg Uncertainty Principal
States it is impossible to determine with perfect accuracy both the position and velocity of a particle at any given point in time
What are the limitations to Bohr’s Theory (of electrons)?
○Didn’t explain the many lines on the emission line spectra of elements other than hydrogen
○Didn’t take into account that an electron has a wave motion, i.e. the electron can’t travel in a precise path at a precise distance from the nucleus
○In conflict with Heisenburg’s Uncertainty Principal as we can only refer to the probability of finding an electron in a region of space
○Didn’t take into account the presence of sublevels
Orbital
Region in space within which there is a high probability of finding an electron
Who used mathematical equations to work out the probability of finding an electron in any sublevel?
Schrodinger
What shape is the s orbital?
spherical
What shape is the p orbital?
dumbbell shape centres on the x, y and z axis
Sublevel
Subdivision of the main energy levels and consists of one or more orbitals of the same energy
