Topic 1: Atomic structure (physical chemistry) Flashcards
What do the chemical properties of elements depend on
electronic configuration
What does the arrangement of electrons in energy levels link to
the way elements are organised in the periodic table
How can chemists measure the mass of atoms and molecules to a high degree of accuracy
By using a mass spectrometer (time of flight)
What is the mass and charge of protons
Mass = 1
Charge = +1
What is the mass and charge of electrons
Mass = 1/1835
Charge = -1
What is the mass and charge of neutrons
Mass = 1
Charge = 0 (neutral)
What is the overall charge of the nucleus of an atom
positive (contains protons and neutrons)
What is the overall charge of an atom
Neutral (positive and negative charges cancel eachother out)
What is an isotope
isotopes are atoms of the same element with the same number of protons but a different number of neutrons
what does a mass spectrometer give accurate information about
relative isotopic mass and relative abundance of isotopes
What are the steps for time of flight
Ionisation, acceleration, ion drift, detection
What is ionisation energy
the amount of energy required to remove one mole of electrons from one mole of gaseous atoms of an element to form one mole of gaseous ions.
what are cations
positive ions
What are anions
negative ions
what does the period number show
the amount of energy levels
What does the group number show
the amount of electrons in the outer level
how do you calculate mr
the mean mass of an atom / 1/12 x mean mass of a c-12 isotope
how do cations and anions form
cations by losing an electron
anions by gaining an electron
what are polyatomic ions
ions that possess more than one atom but have one overall charge
what is an ionic compound
when a negative ion joins with a positive ion
How do you work out ionic formula
drop the charges then swap
Define relative atomic mass
the average mass of an atom of an element relative to 1/12 the mass of an atom of carbon-12
State two features of the current model that arent shown in Rutherford’s model
-the current model includes protons and neutrons
-the current model shows electrons in different energy levels
Which atom contains only two unpaired electrons
oxygen
State two differences between the plum pudding model and the model of atomic structure used today
-nucleus contains protons and neutrons
-electrons are now arranged in energy levels
State which of the elements magnesium and aluminium has the lower first ionisation energy
Aluminium has the lower first ionisation energy as it’s outer electron is in the 3rd energy level. This means that the outer electron is easily lost.
What does time of flight record
the time it takes for ions of each isotope to reach a detector
What occurs during the first step of TOF
ionisation –> a sample of an element is vapourised and injected into the mass spectrometer where a high voltage is passed over the chamber. This causes electrons to be removed from the atoms creating +1 ions. Or the sample is hit with high energy electrons that knock an electron off.
What is the second stage of TOF
Acceleration –> these positively charged ions are then accelerated to a negatively charged detection plate
What occurs during the third stage of TOF
Ion drift –> the ions are then deflected by a magnetic field into a curved path. The radius of their path is dependent on their charge and mass of the ion
What occurs during the final stage of TOF
Detection –> when the positive ions hit the negatively charged detection plate they gain an electron thus producing a current. The size of the current is proportional to the relative abundance of an isotopes
how do you calculate kinetic energy
Ke = 1/2mv^2
How do you calculate velocity
square root 2Ke / m (mass)
How do you calculate time
distance (length) / velocity
distance / square root 2Ke / m
What are the positive ions called
molecular ions
complete the sentence —> the heavier the ion
the slower it will accelerate and the longer it will take to hit the detector
What is time of flight proportional to
square root the mass of the ions
what are the two ways a sample can be ionised
either electron impact or electrospray ionisationw
what does abundance tell us
how common each isotope is
the size of current is proportional to the abundance
true or false –> all ions with the same charge have the same kinetic energy as eachother
true
what is m/z ratio
the ratio of the mass of each ion to its charge
define empirical formula
the simplest whole number ratio of atoms of each element in a compound
Explain how ions are accelerated, detected and abundanced in a mass spectrometer
-ions are accelerated by attraction to negatively charged plate
-the ions are detected by gaining an electron
-abundance is proportional to the size of current flowing in the detector
Describe how ions are formed in a mass spectrometer
1) electrospray ionisation –> a sample is dissolved in a volatile solvent. The sample is then passed through a positvley charged needle thus causing each molecule gaining a proton
2) electron impact –> high energy electrons are fired at the sample which then knocks off an electron thus forming a positive ion
What are the two types of ionisation
electron impact and electrospray ionisation
Why is it necessary to ionise a molecule when measuring their mass
-ions only will interact with and be accelerated by an electric field
-only ions would be attracted to the negatively charged plate
-only ions will created a current
What is the purpose of mass spectrometry
to identify the masses of unknown chemical compounds
How are we able to determine the identity of a compound by knowing its mass
each compound has its own relative formula mass. By knowing the mass we can work out the elements present.
What is a summary of how the mass spectrometer works
-a gas sample enters the spectrometer
-a filament in the spectrometer ionises the gas using high energy electrons
-the ions are accelerated with an electric field
-the lighter ions will travel faster
-ions are separated and deflected by mass using a magnetic field
what is the equation for electron impact
X(g) –> X+(g) + e-
What occurs during electron impact
an electron is knocked off thus forming a positive ion
what is the equation for electrospray ionisation
X (g) + H+ (g) —> XH+ (g)
why are positive ions accelerated
so they all have the same kinetic energy
what type of compounds can only be used in a mass spectrometer
gaseous compounds
what does the flight of each particle depend on
velocity
What occurs during detection
1) the positive ion hits a negatively charged electric plate. When they hit the detector plate the positive ions gain electrons from the plate
2) this generates an electric current. (note if there were not ions, this would not be possible)
3) the abundance of ions is proportional to the size of current
what is the m/z ratio
the mass of ions (mass to charge)
What does each peak on the spectrum represent
an isotope
How do you calculate relative isotopic mass
1) calculate percentage abundance of unknown isotope
2) input values into equation
3) rearrange
How many isotopes does chlorine have
2
35Cl-35Cl +
35Cl-37Cl+ 37Cl-35Cl+
37Cl-37Cl+
How many isotopes does bromine have
2
81Br and 79Br
what is the abundance of chlorine 35 and 37
35 = 75%
37 = 25%
Define diatomic
a molecule possessing two molecules that are identical
What is ionisation energy
ionisation energy is the amount of energy required to remove one mole of electrons from one mole of gaseous atoms of an element to form one mole of gaseous ions
What are the units of ionisation energy
KJ/mol
do group 1 elements have a lower or higher ionisation energy than nobel gases
lower
What is first ionisation energy affected by
-size of nuclear charge
-distance of outer electron from nucleus (atomic radius)
-shielding effect of inner electrons
-spin pair repulsion
what happens to ionisation energy across a period
it increases
what happens to ionisation energy down a group
it decreases
why does ionisation energy increase across a period
-atomic radius decreases –> outer shell is pulled closer to the nucleus
-becomes harder to remove an electron as more energy is needed
Why is there a large decrease in ionisation energy from one period to another
There is increased distance between the nucleus and the outer electrons as you have added a new shell
There is increased shielding by inner electrons because of the added shell
These two factors outweigh the increased nuclear charge
why does ionisation energy decrease down a group
Ionisation energy down a group decreases , distance between nucleus and outer electron increases, shielding increases, easier to remove outer electron
What is successive ionisation energy
the sequence of ionisation energies
why do successive ionisation energies increase
once you have removed an electron you have formed a positive ion. as more electrons are removed the attractive forces increase due to decreases in shielding and an increase in proton to electron ratio. the increase in ionisation energy is dependent on electron configuration
why is it more difficult to remove electrons from principle quantum shells that get closer to the nucleus
as there is less shielding and an increase in attractive forces between the electrons and nuclear charge.
What can successive ionisation energy data be used for
Predict or confirm the simple electronic configuration of elements
Confirm the number of electrons in the outer shell of an element
Deduce the Group an element belongs to in the Periodic Table
By analyzing where the large jumps appear and the number of electrons removed when these large jumps occur, the electron configuration of an atom can be determined
Where are electrons found
energy levels/quanta shells
how many electrons are found in the first shell
2
How many electrons are found in the second shell
8
How many electrons are found in the third shell
18
How many electrons are found in the fourth shell
32
How many electrons are found in each subshell (s, p ,d , f)
s = 2
p = 6
d = 10
f = 14
From their electron configuration how can you tell that both neon and krypton are noble gases
Both electron configurations end in p6 = full outer shell
what do the different blocks for elements tell us
the final sub shell of that element
what is the lowest energy level and why
N=1 as the closer to the nucleus the lower the energy of that level
what is an exception when filling sub shells and why
4s is filled before 3d as 4s has lower amounts of energy
what are the 2 exceptions of elements
Copper and chromium –> prefer to have 1 electron in 4s and 1 in 3d
What is the electronic configuration of copper
1s2 2s2 2p6 3s2 3p6 4s1 3d10
What is the electronic configuration of chromium
1s2 2s2 2p6 3s2 3p6 4s1 3d5
What can the sub shells be further split into
orbitals
what are orbitals
regions where there is a high chance of finding an electron in a sub shell
what is the shorthand version of electronic configuration
part of the notation is substituted with the previous noble gas
what type of reaction is ionisation
endothermic
what is the attraction between the positive nucleus and electrons called
electrostatic force of attraction
true or false - removing electrons requires energy
true
what is the success criteria of first ionisation energy
-must be one mole of the element
-must form a plus one charge
-must be in a gaseous state
what is successive ionisation energy
the energies required to remove any further electron
Define second ionisation energy
the energy required to remove one mole of electrons from one mole of gaseous +1 ions to form one mole of 2+ ions in the gaseous state
What is the interaction between the nucleus and electrons called
electrostatic forces of attraction
what are the 2 types of forces occuring in an atom involving the nucleus and electrons
-electrostatic forces of attraction between nucleus and electrons
-repulsion between electrons on the energy levels
what does if mean if an element has a higher ionisation energy
there would be a stronger electrostatic force of attraction as more energy would be required to remove the electron
what does the amount of energy required to overcome the electrosatic force of attraction depend on
-nuclear charge
-atomic radius
-shielding
-attraction
would Li or Li+ have a greater nuclear charge and why
Li+ has the highest ionisation energy and therefore has a greater nuclear charge than Li due to a higher proton:electron ratio. This means that there is a greater attraction between the nucleus and outer electron so would require more energy to overcome.
what affects nuclear charge
the proton:electron ratio
(more protons than electrons = higher nuclear charge) –> only for ions
or
atomic charge
Explain why atomic radius decreases across period 3 from sodium to chlorine
nuclear charge increases which means that shielding is similar
outer electron is pulled closer to the nucleus due to attraction
explain why the second IE of calcium is lower than the second IE of potassium
calcium’s outermost electron is further from the nucleus so there is more shielding
define atomic radius
the distance between the nucleus and the outermost electron
what happens to ionisation down a group
decreases
what happens to ionisation energy across a period
increases
what happens to ionisation energy down a group in terms of atomic radius and shielding
-down a group ionisation energy decreases as the outermost electron becomes further from the nucleus so the attraction decreases, the attraction is also shielded
what element in group 1 has the highest ionisation energy
hydrogen as atomic radius is smallest so the outermost electron is closer to the nucleus. This means that attraction is greater
what happens to ionisation energy across a period (long answer)
ionisation energy increases as atomic number increases so nuclear charge increases
-attraction is stronger which brings the shell closer to the nucleus reducing the atomic radius
define shielding
when there repulsion due to inner electrons shield, the nucleus from the outer electrons. It increases with increasing number of occupied shellsw
what happens to shielding down a group
as you go down group shielding increases so atomic radius increases so there is weaker electrosatic force of attraction between the nucleus and outer electron
how can you tell what group an element is in by their ionisation energy
-the group in which can element can be found is shown by where the first big jump in ionisation energy occurs e.g there is a big jump between the 5th and 6th ionisation energy, therefore the element is in group 5
Explain why the atomic radius decreases across period three from sodium to chlorine
nuclear charge increases which means shielding is similar
where would the big jump be if an element was in group 1
in the 2nd ionisation energy
why is there a jump shown in an IE graph
the next electron to be removed is closer to the nucleus and therefore experiences a greater electrosatic force of attraction. There will be less shielding.
what does it mean if more electrons are being removed in terms of NASA
the p:e ratio increases which means the nuclear charge of the ion increases
explain the trends in ionisation energy across period 2 from Li to Ne
-1st ionisation energy increases across a period due to an increased nuclear charge
-shielding is similar and there is a stronger attraction between the nucleus and outer electron
-There is some deviation between Be and B (b lower than be) as 2p is higher in energy than 2s
-There is also a dip between N and O (o is lower than n) as 2 electrons in 2p need a pair which causes repulsion
what are the exceptions for ionisation energy in period 3
dips at Al and S
how can the dip in IE graphs be explained
through electronic configuration
why does Al have a lower ionisation energy than Mg in terms of electronic configuration
This is because the electron for Al is removed from a 3p orbital. 3p is higher in energy than 3s so it takes less IE to remove the electron. 3p subshell also experiences more shielding as it is further for the nucleus so electrosatic force of attraction is weakened.
how many orbitals are there in the s,p and d subshells
s = 1 orbital
p = 3 orbitals
d = 5 orbitals
why is the second ionisation energy of boron greater than the first ionisation energy
the electron being removed is closer to the nucleus
why do elements have different chemical properties
different electronic configuration
true of false - the element with the lowest mz value is deflected most by the magnetic field
true
why is there a dip in IE graph for sulfur
paired electron in 3p orbital results in spin pair repulsion
what are the requirements for box notation
must be spin paired, must fill up orbitals singly first then paired
what is more stable the 3p3 subshell or 3p4
3p3 orbital is more stable than 3p4 orbital as electrons are more stable unpaired than paired electrons due to less spin pair repulsion
what has a lower ionisation energy 3p3 or 3p4 orbital
3p4 orbital has lower ionisation energy. Due to spin pair repulsion in the p orbital it is more unstable. this means that less energy is required to remove an electron
why does sulfur have a lower ionisation energy than phosphorus
sulfur has a lower ionisation energy than phosphorus as the electron removed is from a 3p paired orbital; there is added repulsion
why does atomic radius increase across period 3
periodicity
define periodicity
a repeated trend in properties of elements across a period
why is ionic radius smaller for positive ions
as each ion has one fewer shells of electrons compared to their respective atoms. There is less electron-electron repulsion and nuclear charge is higher due to greater p:e ratio
define melting point
solid to liquid
what are the factors affecting high melting point
strength of giant covalent bonds, ionic bonds or metallic bonds being broken and therefore the number that are breaking
what are the factors affecting low melting point
strength of intermolecular forces and therefore the number of intermolecular forces being broken
why will Al3+ have a smaller atomic radius than Na+
Al3+ will have smaller atomic radius as it has greater nuclear charge and therefore stronger electrosatic force of attraction.
why does melting point increase from Na to Al
ions have greater ionic charge and are smaller than Na. Aluminum has more delocalised electrons so greater charge density
Greater ionic charge
Smaller atomic radius
More delocalised electrons
define electronegativity
the ability of an atom to attract electrons in a covalent bond
true or false - the same elements have the same electronegativity
true
what happens to electronegativity across a period
it increases - electrons are more attracted as atomic radius decreases. Shielding is similar and nuclear charge increases
what happens to electronegativity down a group
decreases
what happens to melting points across period 3
gradual increase from Na to Al due to more delocalised electrons so there is an electrosatic attraction between those electrons and positive metal ions
Huge increase to Si due to giant covalent molecule
Decrease from P to Cl due to simple covalent bond so lower melting point
Argon has lowest melting point as it is monoatomic so has very weak intermolecular forces
identify the S block element that has the highest first ionisation energy
Be (beryllium)
true or false - the greater the mass the greater the kinetic energy
true
how does the graph of successive ionisation energy give evidence for shells
-big jumps show that an electron is being removed from an inner subshell
Deduce which of Na+ and Mg2+ is the smaller ion
Mg2+ is the smaller ion –> greater number of protons so stronger attraction between the nucleus and outer electron. This means that the outer electron is pulled closer to the nucleus
true or false -> the isotope with the largest mass/mz value will be deflected most
false –> isotope/ion with the smallest mass/mz value will be deflected the most
what are the two most important aspects of NASA when mentioning ionisation trends across a period
-nuclear charge
-attraction
(sometimes shielding)
how many electrons are in a D orbital
2
how is an element classified as its s,p,d,f block in the periodic table
according to
its position in the Periodic Table, which is determined by
its proton number.
Equation for the 3rd ionisation energy of Mg
Mg2+ (g) –> Mg3+ (g) + e-
Explain why the third ionisation energy of magnesium is much higher than the
second ionisation energy of magnesium.
-Electron being removed is closer to the nucleus
-greater attraction and is less shielded
how many isotopes does hydrogen have and what are they
3 –> Protium (1), (Deuteurium (2), Tritium (3)
identify the element in period 3 that has the highest 2nd ionisation energy
Na
Identify the element in period 4 with the largest atomic radius
Potassium (K)
Smallest nuclear charge. Similar shielding
what colour is hydrated copper sulfate
blue
equation for the third ionisation energy of managnese
Mn2+ (g) → Mn3+ (g) + e−
deduce the formula of the compound that contains 2+ ions and 3- ions that both have the same electronic configuration as argon
Ca3P2
why is mg2+ a smaller ion
-larger nuclear change
-same shielding
state how the relative molecular mass (mr) of a covalent compound is obtained from its mass spectrum
highest mz value = mr
Explain why a sodium atom is larger than a chlorine atom
-a chlorine atom has more protons in its nucleus than a sodium atom
-both have 3 shells of electrons
-electrons more strongly attracted to Chlorine nucleus so smaller atomic radius
true or false - electrospray ionisation is used for larger molecules so fragmentation doesnt occur
true
why is more energy required
-electron removed from subshell closer to nucleus
-electron being removed is less shielded
concentration
moles / volume
p6 = more energy = why?
p6 = noble gas
unreactive = more energy required to remove an electron
ion that has a charge of 2+ with the same electronic configuration as krypton
Sr2+
