s1.3 electron configurations Flashcards
what is the electromagnetic spectrum?
the EM spectrum is the range of wavelengths, or frequencies, of EM radiation. higher energy corresponds to higher frequency and shorter wavelength. lower energy corresponds to lower frequency and longer wavelength
what equation is related to the EM spectrum?
c = f x λ
the speed of light (‘c’) is constant and has a value of 3.00 x 10^8 m/s
as you can see from the spectrum, frequency (‘f’) is inversely proportional to wavelength (‘λ’)
what is line spectra?
white light is made up of a range of colours. these colours can be separated by splitting white light with a glass prism to obtain a spectrum. every element in the periodic table produces a unique line spectrum when heated, consisting of specific colours at specific wavelengths seen as thin bands
what are the three types of line spectra?
a continuous spectrum shows all the wavelengths, or frequencies on a coloured background
an absorption spectrum shows black lines on a coloured background
an emission spectrum shows coloured lines on a black background
each element has unique absorption and emission spectra and they can be used to identify unknown elements
what does line spectra tell us about electrons?
line spectra tells us that the emitted light from atoms can only be certain fixed frequencies - it is quantised. electrons can only possess certain amounts of energy - they cannot have any energy value
how are line spectra produced?
the bohr model of the atom has the protons and neutrons located in the nucleus and the electrons located in energy levels around the nucleus. electrons only exist in stationary orbits of discrete energy levels and electrons in the same energy level have the same amount of energy.
electrons can transition between energy levels by either absorbing or emitting specific amounts of energy. this energy is in the form of small packets of energy called photons.
if an electron absorbs an exact amount of energy, it will transition to a higher energy level. if an electron emits an exact amount of energy, it will transition to a lower energy level - this photo represents the energy difference between the 2 levels.
what is the flame test?
the flame test is an analytical technique. it is used to identify the presence of some metals. the flame test is an atomic emission
how is a hydrogen emission spectrum produced?
a hydrogen discharge tube is filled with hydrogen gas at low pressure. a spectroscope is used to split the light into its different wavelengths
what does the hydrogen emission spectrum show?
electron transitions to the first energy level (n=1) emits the highest amount of energy and corresponds to the UV region of the EM spectrum.
electron transitions to the n=2 energy level emit energy that corresponds to the visible light region of the EM spectrum.
electron transitions to the n=3 energy level emit energy in the infrared region of the EM spectrum.
the longer the arrow, the greater the amount of energy emitted
what is the principal quantum number?
a shell or electron level is a group of atomic orbitals with the same principal quantum number (n). the principal quantum number (n) indicated the electron level that the electrons occupy.
what are principal energy levels?
electrons are located in principal energy levels (main energy levels). the first main energy level (n=1) has the lowest energy and energy increases as the value of n increases. each main energy level can hold a maximum of 2n² electrons.
what are the sub-levels in the atom?
each main energy level is split into sub-levels.
-> n=1 has 1 sub level (1s)
-> n=2 has 2 sub levels (2s, 2p)
-> n=3 has 3 sub levels (3s, 3p, 3d)
-> n=4 has 4 sub levels (4s, 4p, 4d, 4f)
what is an orbital?
an orbital is a region in space where one is likely to find an electron (heisenburg uncertainty principle). orbitals can hold up to two electrons as long as they have opposite spin; this is known as pauli’s exclusion principle
what shape do orbitals take?
s orbital -> spherical, one in every level
p oribital -> dumb bell, three in every level from 2 up
d orbital -> various, five in levels from 3 up
f orbital -> various, seven in levels from 4 up
what is electron configuration?
the arrangement of electrons in orbitals is called electron configuration. only a maximum of 2 electrons can occupy the same atomic orbital. those 2 electrons will have opposite spins - the spin is based on a magnetic property
what is the aufbau principle?
the aufbau principle states that electrons are placed into orbitals of lowest energy first
what is hund’s rule?
hund’s rule states that if more than one degenerate orbital in a sub-level is available, electrons occupy separate orbitals with parallel spins. always fill orbitals of equal energy with one electron first and then add the second electron once each orbital has one electron in it
what is the electron configuration of ions?
metals lose electrons when they form ions. note that the first row d-block elements (sc - zn) lose their 4s electrons first when they form ions
what is first ionisation energy?
first ionisation energy is the energy required to remove one electron from each atom (to infinity) in one mole of gaseous atoms to form one mole of gaseous 1+ ions
what factors affect first ionisation energy?
- nuclear charge: the greater the nuclear charge (number of protons), the greater the effective nuclear attraction experienced by the outer electrons so it requires more energy for the electron to be removed
- atomic radius: the greater the atomic radius, the less effective nuclear attraction experienced by the outer electrons
- electron shielding (caused by the inner shells of electrons repelling the outer electrons): the more inner shells there are, the larger the shielding effect and the smaller the effective nuclear attraction experienced by the outer electrons
why does 1st IE decrease as you go down the group?
despite an increased nuclear charge, the outer shell is easier to remove due to increased shielding and greater atomic radii. the outer electron is held less strongly and is easier to remove, meaning there is less effective nuclear attraction
why does 1st IE generally increase as you go across a period?
there is increased nuclear charge, a slightly decreased atomic radii and a similar amount of shielding. the outer electron is held more strongly and harder to remove, meaning there is more effective nuclear attraction
why is there a decrease in energy in 1st ionisation energy between mg and al?
mg has the electron configuration 1s2 2s2 2p6 3s2 while al has the electron configuration 1s2 2s2 2p6 3s2 3p1.
the outer electron is removed from the 3p subshell in mg which has subshell shielding from the 3s subshell and is further away from the nucleus. this means there is less effective nuclear attraction
why is there a decrease in 1st ionisation energy between p and s?
p has the electron configuration 1s2 2s2 2p6 3s2 3p3. s has the electron configuration 1s2 2s2 2p6 3s2 3p4.
for s, the electron is removed from a doubly occupied p orbital. the outer electron will experience electron pair repulsion in the 3p subshell, so it requires less energy to remove than an electron in a half-filled orbital
