Arrangement of electrons

Energy level

the fixed energy value that an electron in an atom may have

Ground state

of an atom is one in which the electrons occupy the lowest available energy levels

What is the name given to the visible regein of the hydrogen line spectra?

Balmer series

Which energy level do electrons fall to to produce the Balmer series?

n = 2

What is an emission spectrum?

light is emitted from a sample of a gaseous element which has been excited

If hydrogen has only one electron, why is there more than one line on its emission spectrum?

• with a sample of hydrogen there are millions of hydrogen atoms

• when energy is supplied not all atoms receive the same amount

• some may jump to higher energy levels

• those that jump to high energy levels may not drop directly back to n = 1, but could drop to an in between level first emitting energy of 2 different wavelengths

What are the different colours produced in the emission spectrum of hydrogen?

Red n=3 → n=2

Blue/green n=4 → n=2

Indigo n=5 → n=2

Violet n6 → n=2

How is the energy of the emitted light related to its wavelength?

• higher energy transitions produce shorter wavelengths → blue and violet light

• lower energy transitions produce longer wavelengths → red light

Why is the line spectrum unique for each element?

• each element has a unique number of electrons in each of its atoms and thus has a unique electron configuration

• in atoms of any element the energy difference between levels is unique to that element

• the electronic transitions/moving from one level to another are unique in terms of energy requirements and energy emission

Bohr’s theory states:

1. electrons occupy fixed energy levels

2. in the ground state, electrons occupy the lowest available energy level

3. if an tom receives energy, it becomes excited and jumps to a higher energy level

4. the energy absorbed by the atom must equal the differences between the ground state and the excited state/the low energy level and the high energy level

5. the excited state is unstable and the electrons fall back down to lower energy levels

6. this releases energy in the form of light, of a definite wavelength which correspond to the different colours seen on line spectra

7. the frequency of light emitted depends on the 2 energy levels and is represented by the equation E₂ - E₁ = hf - E₂ is the higher energy level, E₁ is the lower energy level, h is planck’s constant and f is the frequency of light emitted

What is an absorption spectrum?

shows a continuous spectrum of light with certain wavelengths missing that are absorbed by the element

Atomic Absorption spectrometry - principle

atoms in the ground state absorb light of a particular wavelength characteristic of the element, and absorbance is directly proportional to concentration

Atomic Absorption spectrometry - process

1. sample solution is sprayed into the flame and the sample element is converted into atoms in the element

2. ground state atoms absorb radiation from a source made from the element

3. absorbance is measured

Atomic Absorption spectrometry - use

• detection and measuring concentration of heavy metals

• detection and measuring concentration of water pollutants

How does modern atomic theory describe the behaviour of electrons?

• de Broglie suggested that electrons can behave as a particle and as a wave/ demonstrates wave particle duality

Heisenberg’s uncertainty principle

states that it is impossible to measure at the same both the velocity and the position of an electron

Limitations of Bohr’s theory

• only worked well for hydrogen + wasn’t accurate for higher elements

• did not take into account the fact that the electron had a wave motion

• heisenberg’s uncertianty principle was in conflict with Bohr’s theory

• did not explain sublevels

• did not account for the existence of orbitals

Orbital

a region in space within which there is a high 95% chance of finding an electron

Who calculated the probability of finding an electron within a certain region in space?

Schroedinger

What shape are s orbitals?

sphericalwhat

What shape are p orbitals?

dumbell shaped

Sublevel

a subdivision of a main energy level and consists of one ore more orbitals of the same energy

Aufbau principle

when building up the electron configuration of an atom in its ground state the electrons occupy the lowest available energy levels

Write the electron configuration of Al

Write the electron configuration of Ca

What are the exceptions when writing electron configuration + why?

Chromium + Copper

• a full or exactly half filled energy sublevel has extra stability

Hund’s rule of maximum multiplicity

states that when 2 or more orbitals of equal energy are available, the electrons occupy them singly before ever filling them in pairs

Pauli exclusion principle

states that no more than 2 electrons may occupy an orbital and they must have opposite spin