Flashcards in atomic structure and the periodic table Deck (31):
what is relative mass?
relative mass is the weighted mean mass of an atom of an element compared to 1/12 of the mass of an atom of carbon-12.
what is the relative molecular mass?
the relative molecular mass is the average mass of a molecule or formula unit, compared to 1/12 the mass of carbon-12
how do you work out Ar from isotopic abundance?
multiply each isotopic mass by its % abundance and then divide by 100.
what are mass spectra?
mass spectra are produced my mass spectrometers and can find out things such as the relative isotopic a masses and abundances of different elements.
how do you work out the relative atomic mass from a mass spectrometry graph
multiply each relative isotopic mass by its abundance and then add them together. Next divide the total by the sum of the % abundances (should be 100%)
how does mass spectrometry work?
first the sample is ionised by a bombardment of electrons, then a mass analyser separates the ions by mass to charge ratio e.g magnetic field, finally they hit an ion detector giving an electrical signal which is converted to a digital response and stored in a computer.
how do electrons move around the nucleus
the atoms travel around in quantum shells, these shells are given numbers called quantum numbers.
what is an orbital?
an orbital is the bit of space that an electron moves in, orbitals within the same subshell have the same energy.
what do you have to be aware of when working out electronic configuration?
that the 4s orbital fills up before the 3d orbital as it has a lower energy level.
what are the 3 sections that the periodic table is split into?
it is split into the s-block, the d-block and the p-block.
what is a line spectrum?
a line spectrum show the frequencies of light that are emitted when an electron drops down from a higher energy level.
what is the definition of the fist ionisation energy.
the amount of energy required to remove 1 electron from each atom of 1 mol of gaseous atoms to form 1 mol of gaseous 1+ ions.
what does a high ionisation energy mean?
there i s strong attraction between an electron and the nucleus, so more energy os needed to overcome the attraction and remove the electron.
what are the three factors that effect ionisation energy?
nuclear charge: the more protons there are in the nucleus the more positively charged the nucleus is and the more attraction there is
electron shells: the more electron shells there are the greater the distance between the outer electrons and the nucleus and so the weaker the attraction.
shielding: as the number of elections between the outer electron and the nucleus increases the outer electron feels less attraction towards the nuclear charge.
what its the second ionisation energy?
the second ionisation energy is the energy needed to remove 1 electron in each ion in 1 mol of gaseous 1 + ions to form 1 mole of gaseous 2 + ions.
within each shell why do successive ionisation energies increase?
the increase as they are being removed from a successively positive ion so therefore there is less repulsion between each of the remaining electrons and forever there is a stronger attraction from the nucleus.
when are there big jump in ionisation energy?
when a new shell is broken into.
what is periodicity?
when there are repeating trends in the physical and chemical properties of the elements across each period.
what decides the chemical properties of an element?
the electronic configuration of the element.
what happens to the atomic radius as you go across the period?
the atomic radius decreases as the number of protons increases, this means that the electrons are pulled closer to the nucleus, making the atomic radius smaller.
why does ionisation energy increase across the period?
the tuber of proton is increased so there is a stronger nuclear attraction. all the electrons are roughly the same energy level this means that there is little to no extra shielding or distance effect.
why are there drops between group 2 and 3?
this shows subshell structure. generally it takes more energy to remove an electron from a higher energy subshell than a lower subshell.
explain the drop between groups 5 and 6
this is due to electron repulsion. in general, elements with singly filled or full subshells are more stable than those with partially filled subshells, so have higher ionisation energies.
explain the trend in melting and boiling points in a period.
-for the metals the boiling and melting points increase as the metallic bonds get stronger because e the metal ions have an increasing number of delocalised electrons and a decreasing radius (higher charge density)
-the elements with giant covalent structures such as carbon and silicon have strong covalent bonds, these two have the highest boiling points in thee period.
-next along the period is the simple molecular structures who's melting points depend on the strength of the london forces (increase with electrons)
-finaly the noble gases have the lowest boiling points as the exist as individual atoms resulting in very weak atoms.
what is an isotope?
a form of the same element that has the same number of protons but a different number of electrons.
how do you predict the mass spectra of a diatomic molecule?
first express each of the percentages as decimals; then make stable showing all of the different diatomic molecules, for each of them multiply the isotopes by their abundances to get each of the relative abundances; look for any molecules that are the same and then add them together; divide all of the relative abundances by the smallest to get the smallest whole number ratio and then by working out the relative formula mass of each molecule you can predict the mass spectrometer.
how does the electron emission spectra show evidence for quantum shells?
the emission spectra has clear lines for different energy levels. this supports the idea that energy levels are discrete (the jump between shells)
how do successive ionisation energies provide evidence for quantum electron shells?
who you look at graph with the successive ionisation energies of an element there is usually big jumps. these happen when new sell is broken into. a shell is broken into that is closer to the nucleus so it has a higher ionisation energy.
how does the first ionisation of each element in a period provide evidence for sub-shells?
there are drops between groups 2 and 3, generally it requires more energy to remove an electron form a higher energy sub shell then a lower energy sub shell. as the p orbital that the electrons move into has the shielding provided by the s orbital it has a slightly lower first ionisation energy.
there is also a jump between 5 and 6, is due to electron repulsion. In group 6 the electron is being removed from an orbital containing two electrons - means that it is easier to remove the electrons.
what is spin pairing?
the theory that two elections within an each orbital can spin in opposite directions.