Arrangement of electrons In Atoms Flashcards
(38 cards)
Define energy level.
Energy level is the fixed/discrete amount of energy of an electron.
Define ground state.
The ground state is when all electrons are in the lowest available energy level-most stable state of an atom.
Define excited state.
An excited state occurs when electrons absorb enough energy to be promoted to higher energy levels - it is an unstable state and electrons release energy to drop back down.
Give two ways electrons in an atom can be excited.
Heating the element.
Passing an electric current through the element.
What is an atomic/line emission spectrum?
An atomic emission spectrum is a series of coloured lines that correspond to the specific frequencies of light emitted when electrons in an element are excited.
Explain how the visible line spectrum of hydrogen arises and proves the existence of energy levels.
Ground State: Electron n=1.
Element heated-excited state-promoted to level greater than n=2
Temporary and unstable state falls back to n=2.
This energy is emitted as a photon of light of definite frequency equal to the difference between the energy levels. This frequency shows as a particular colour on the emission line spectrum.
Formula for energy/frequency of emitted photon.
E2 - E1 = hf
What name is given to the visible region of frequency? Which energy level do they drop to?
The Balmer series. All drop to energy level n=2.
What name is given to the invisible infra-red region? What level do they fall to?
Paschen Series. All drop to energy level n=3.
What name is given to the invisible ultra-violet region? What level do they fall to?
Lyman Series. All drop to energy level n=1.
Why is there no yellow line in the hydrogen emission spectrum?
There is no corresponding electron transition in hydrogen that would produce light of frequency that gives a yellow colour.
What are flame tests? Why is it useful?
Heating an element in a bunsen burner will cause that element to produce a characteristic colour.
The element can therefore be identified.
Give two reasons why different elements have different atomic emission spectra.
- Different metals have different transitions between their energy levels.
- Different metals have different number of electrons.
List and explain briefly, three uses of a knowledge of energy levels in everyday life.
- Atomic Absorption Spectrometry (AAS) If white light is passed through an element sample certain light frequencies will be absorbed. Same lines as a line spectrum but they are black marks on the full spectrum.
- Sodium streetlights use sodium vapour in an excited state.
- Fireworks use particular elements to give off their characteristic colours.
The Heisenberg Uncertainty Principle.
It is not possible to ascertain both the position and the momentum of an electron in an atom simultaneously.
Define energy sub level.
A group of atomic orbitals that all have the same energy.
Define dual wave particle nature.
Light and matter exhibit properties of both waves and particles.
Define atomic orbitals.
The region in space around the nucleus of an atom in which electrons are likely to be found.
Aufbau principle
Electrons occupy the lowest available energy level.
Pauli exclusion principle.
No more than two electrons can occupy an orbital, and this they can only do if they have opposite spin.
List three uses of AAS
- Identifying elements present in distant stars.
- Detecting the presence and concentration of heavy metals in water.
- Detecting gunshot residue on clothes in forensics
What was Bohr’s model of an atom?
- An atom consists of a small dense area called the nucleus.
- Electrons are tiny particles that revolve around the nucleus in fixed orbits.
- An electron in any one orbit has a definite amount of energy.
Describe four limitations of Bohr’s theory.
- Energy levels were found to consist of further sub levels.
- Bohr’s explanation only worked for hydrogen emission spectrum and failed to explain many of the lines in other emission spectra.
- Electrons were found to have properties of particles and waves.
- The exact position and velocity of an electron cannot be measured at the same time so they cannot be described as travelling in fixed paths.
Characteristics of s-orbital and s-sub level.
There is one s-orbital in a s-sub level.
Each s-orbital can hold two electrons.
Therefore an s-sub level can hold two electrons.
S-orbital spherical in shape.
