topic 1 - atomic structure and periodic table Flashcards
definition of relative isotopic mass
the mass of one atom of an isotope compared to 1/12th of the mass of one atom of carbon 12
definition of relative molecular mass
the average mass of a molecule compared to 1/12th of the mass of one atom of carbon 12
definition of relative atomic mass
the average mass of one atom compared to 1/12th of the mass of one atom of carbon 12
why do isotopes have similar chemical properties
because they have the same electronic structure.
they may slightly varying physical properties because they have different masses
what is the mass spectrometer
can be used to determine all the isotopes present in a sample of an element and therefore identify elements
what is the parent ion/molecular ion
the peak with the largest m/z however, will be due to the complete molecule and will be equal to the Mr of the molecule
what are the uses of mass spectrometers
- mass spectrometers have been included in planetary space probes so that elements on other planets can be identified. elements on other planets can have a different composition of isotopes
- drug testing in sport to identify chemicals in the blood and to identify breakdown products from drugs in the body
- quality control in pharmaceutical industry and to identify molecules from sample with potential biological activity
- radioactive dating to determine age of fossils or human remains
definition of first ionization energy
the energy required when one mole of gaseous atoms forms one mole of gaseous ions with a single positive charge
definition of second ionization energy
the energy required when one mole of gaseous ions with a single positive charge forms one mole of gaseous ions with a double positive charge
what are the factors that affect ionization energy
1- attraction of the nucleus ( the more protons in the nucleus the greater the attraction )
2- the distance of the electrons from the nucleus ( the bigger the atom the further the outer electrons are from the nucleus and the weaker the attraction to the nucleus )
3- shielding of the attraction of the nucleus ( an electron in an outer shell is repelled by electrons in complete inner shells, weakening the attraction of the nucleus)
what information does the successive ionization energy give us
the electronic structure for that element
why are successive ionization energies always larger
the second ionisation energy of an element is always bigger than the first ionisation energy.
when the first electron is removed a positive ion is formed.
the ion increases the attraction on the remaining electrons and so the energy required to remove the next electron is larger.
how are ionization energies linked to electronic structure
the electron is in an inner shell closer to the nucleus and therefore attracted much more strongly by the nucleus than the outer electron
it also does not have shielding by inner complete shells of electrons
why does helium have the largest first ionization energy
it’s first electron is in the first shell closest to the nucleus and has no shielding effects from inner shells. helium has a bigger first ionization than hydrogen as it has one more proton
why do first ionization energies decrease down a group
as one goes down a group, the outer electrons are found in shells further from the nucleus and are more shielded so the attraction of the nucleus becomes smaller
definition of periodicity
Periodicity is the repeating pattern in the properties of elements across different periods of the periodic table.
reasons for an increase in first ionization energy across a period
– Across a period, the nuclear charge increases (more protons).
– Electrons are added to the same energy level, so there is no significant increase in shielding.
– The atomic radius decreases,as electrons are pulled closer to the nucleus.
– Therefore, the attraction between the nucleus and the outer electron increases, requiring more energy to remove the first electron.
reasons for a decrease in first ionization energy down a group
– Down a group, the atomic number increases, so there are more electron shells.
– This increases the atomic radius and electron shielding.
– The outer electron is further from the nucleus and is less strongly attracted.
– Therefore, less energy is needed to remove the outer electron.
definition of successive ionization energy
Successive ionisation energy is the energy required to remove each electron in turn from one mole of gaseous ions, each with one more positive charge than the last.
how did ideas about electronic configuration develop
- the fact that atomic emission spectra provide evidence for the existence of quantum shells
- the fact that successive ionization energies provide evidence for the existence of quantum shells and the group to which the element belongs
- the fact that the first ionization energy of successive elements provides evidence for electron subshells
how is ionization energy influenced by the number of protons
– As the number of protons increases, the nuclear charge increases.
– This creates a stronger electrostatic attraction between the nucleus and the outer electrons.
– Therefore, more energy is required to remove an electron, so the ionisation energy increases.
how is ionization energy influenced by the electron shielding
– Electron shielding is caused by inner electron shells repelling outer electrons.
– As shielding increases, the attractive force from the nucleus on the outer electrons decreases.
– This makes it easier to remove an outer electron, so the ionisation energy decreases.
how is ionization energy influenced by the electron subshell from which the electron is removed
– Electrons in different subshells (s, p, d) have different energies.
– Electrons in a higher-energy subshell (e.g. p) are further from the nucleus and are less strongly attracted.
– Therefore, it requires less energy to remove an electron from a p-subshell than from an s-subshell in the same shell.
– So, ionisation energy is lower when the electron is removed from a higher-energy subshell.
