3.1.1 Atomic Structure Knowledge Flashcards
what is the relative mass of a proton?
1
what is the relative mass of a neutron?
1
what is the relative mass of an electron?
1/1840
what is the relative charge of a proton?
1+
what is the relative charge of a neutron?
0
what is the relative charge of an electron?
1-
what is the atomic number?
total number of protons in an atom
what is the mass number?
total number of protons and neutrons in a nucleus
what is an isotope?
an atom with the same number of protons but different number of neutrons
why do isotopes have similar chemical reactions?
isotopes of the same element have the same chemical properties because they have the same electron configuration
what is a positive ion?
cation
what is a negative ion?
anion
when was the Solid Sphere model invented?
1803
who invented the Solid Sphere model?
John Dalton
summarise the solid sphere model
- All matter is composed of extremely small particles called atoms.
- Atoms of a given element are identical in size, mass, and other properties. Atoms of different elements differ in size, mass, and other properties.
- Atoms cannot be subdivided, created, or destroyed.
when was the plum pudding model invented?
1904
who invented the plum pudding model?
jj thomson
summarise the plum pudding model
- electrons embedded in a uniform sphere of positive charge.
- The positive matter was thought to be jelly-like.
- The electrons were somewhat mobile. As they got closer to the outer portion of the atom, the positive charge in the region was greater than the neighbouring negative charges and the electron would be pulled back more toward the centre region of the atom.
when was the nuclear model invented?
1911
who invented the nuclear model?
ernest rutherford
summarise the nuclear model
a small and dense positively charged nucleus surrounded by a cloud of electrons.
when was the planetary model invented?
1913
who invented the planetary model?
niels bohr
summarise the planetary model
small positive nucleus with electrons orbiting the nucleus in energy shells
when was the quantum model invented?
1926
who invented the quantum model?
erwin schrodinger
summarise the quantum model
the electron is a wave and tries to describe the regions in space, or orbitals, where electrons are most likely to be found.
describe the process and findings of the gold foil/alpha particle experiment
- Rutherford fired He^2+ ions at a sheet of gold foil
- When the He^2+ ions arrived on the other side, he concluded that most of the atom is empty space
- A very small number of the He^2+ ions were detected on the same side as the source. He concluded that the atom must have a small, positive nucleus
define first ionisation energy
the amount of energy required to remove one mole of electrons from one mole of atoms in the gaseous state, units kJ mol^-1
what element has the highest 1st IE? and why?
Helium has the highest 1st IE of all elements; it has more protons than Hydrogen and only one shell so the same shielding as Hydrogen
does nuclear charge increase or decrease down a group?
increase
does nuclear charge increase or decrease across a period?
increase
does atomic radius increase or decrease across a period?
decreases - no. shells stays the same but nuclear charge increases
does atomic radius increase or decrease down a group?
increase - no. shells increases so amount of shielding increases
does shielding increase or decrease down a group?
increases - no. shells increases
does shielding increase or decrease across a period?
stays the same - no. shells stays the same
does first ionisation energy increase or decrease down a group? why?
decreases:
- atoms increase in atomic radius, due to more shells
- more shielding
- weaker attraction from nucleus to electron in outer shell ⇒ less energy required to remove
does first ionisation energy increase or decrease across a period?
generally increases - exceptions are Boron and Oxygen in P2, and Aluminium and Sulphur in P3
what are 3 key factors that influence ionisation energy?
nuclear charge
distance from the nucleus
shielding
why do IE’s 1-3 of Boron increase slowly, then a jump on the 4th?
- IEs 1-3 increase slightly because each electron is being removed from a more positive ion each time
- This means the attraction between the electrons and protons becomes stronger as there are less electrons being attracted by the same no. protons
- the 4th electron is removed from a shell much closer to the nucleus and so is much more strongly attracted, therefore requiring more energy to remove
describe the trend of 2nd IE’s across a period, in relation to first IEs
After the first IE trend, across a period, each ion/element jumps 1 place left on the graph (e.g. the 2nd IE of Be [so from Be+ to Be2+] is similar to the 1st IE of Li [Li to Li+])
Explain the general trend in IEs across P2
- there is a general increase in IE across P2
- this is because across P2 there is a greater nuclear charge and the same amount of shielding
- so a greater attraction between nucleus and outermost electron, meaning more energy is required to remove it
Explain why Boron is lower in IE than Beryllium, despite coming after it in P2
- the first electron removed from Be is from a 2s sublevel
- the first electron removed from B is from a 2p sublevel
- the 2s sublevel is lower in energy than 2p
- therefore less energy is needed to remove the electron from B (as electron from higher sublevel)
Explain why Oxygen is lower in IE than Nitrogen, despite coming after it in P2
- the first electron removed from N is from a 2p sublevel and is unpaired
- the first electron removed from O is from a 2p sublevel, too, but it is from a paired orbital
- this means O has a lower IE due to electron pair repulsion, therefore less energy is needed to remove the electron from O
Explain the general trend in IEs across P3
- there is a general increase in IE across P3
- this is because across P3 there is a greater nuclear charge and the same amount of shielding
- so a greater attraction between nucleus and outermost electron, meaning more energy is required to remove it
Explain why Aluminium is lower in IE than Magnesium, despite coming after it in P3
- the first electron removed from Mg is from a 3s sublevel
- the first electron removed from Al is from a 3p sublevel
- the 3s sublevel is lower in energy than 3p
- therefore less energy is needed to remove the electron from Al (as electron from higher sublevel)
Explain why Sulphur is lower in IE than Phosphorus, despite coming after it in P3
- the first electron removed from P is from a 3p sublevel and is unpaired
- the first electron removed from S is from a 3p sublevel, too, but it is from a paired orbital
- this means S has a lower IE due to electron pair repulsion, therefore less energy is needed to remove the electron from S
why is Mg not lower in IE than Na, DESPITE the electron being from a paired orbital and same subshell?
this is because there is only 1 s orbital, in Mg and Na, compared to the 3 p orbitals in S and P for example, so the electron pair repulsion is outweighed by the nuclear charge
Why is Li a bigger atom than Be?
- Both have the same number of shells so they have the same shielding
- But, Be has more protons so the nucleus attracts the outermost electrons more strongly
Why is Li a bigger atom than F?
- both atoms have the same number of shells so have the same shielding
- F has a higher nuclear charge so the nucleus attracts the outermost electrons more strongly
Why is Li a bigger atom than He?
- Li has an extra electron shell and is further away from the nucleus
- The outermost electron is more shielded which means it is less strongly attracted to the nucleus
Why is Li+ a smaller ion than F-?
- an Li+ ion only has one shell so the outermost electrons experience less shielding
- This means they are more strongly attracted to the nucleus as they are closer to it
give the order of organisation of electron configuration
Energy level ⇒ subshell ⇒ orbital
what is an orbital?
a region within an atom where it is most likely to find an electron; can hold up to 2 with opposite spins
what shape is an s orbital?
spherical
what shape is a p orbital?
dumbbell
what does the large number refer to in electron configuration?
the energy level of the electron
what does the letter refer to in electron configuration?
the subshell of the electron
what does the small number refer to in electron configuration?
the number of electrons in that subshell
describe how orbitals fill up in electron configuration
- orbitals of lower energy are always filled first (closest to nucleus)
- atomic orbitals of the same energy fill up singly before electrons pair up (Hund’s Rule)
- no orbital can have more than 2 electrons
how does the block an element is in, relate to its electron configuration?
each element is placed in the position of its highest energy electron; this means the block that the element is in, determines which type of orbital its highest energy electron is in.
why are d-block elements more stable when they have a full or, or exactly half full, subshell?
as this is a lower energy configuration
what is a mass spectrometer?
machine used to analyse elements or compounds; can accurately determine Ar of atoms or Mr of molecules
what 2 factors do mass spectrometers measure?
relative abundance
mass/charge (m/z) ratio
what are the 4 main steps in TOF mass spectrometry?
ionisation
acceleration
ion drift
detection
describe the full process of TOF mass spectrometry
- Vacuum: the entire machine is a vacuum inside to prevent any of the particles being tested colliding with molecules from the air
- Ionisation: sample particles gain a positive charge through electron impact or electrospray ionisation
- Acceleration: the positive ions are attracted to a negatively charged plate and accelerate towards it. The amount they accelerate depends on m/z ratio (high m/z ratios will accelerate to lower speeds than low m/z ratios). Once accelerated, all ions have the same kinetic energy
- Ion Drift: some ions will pass through a hole in the negatively charged plate, forming a beam of particles which travel along the ‘flight tube’ towards the detector. Because they are travelling at different speeds, they start to drift further apart.
- Detection: different m/z ratio ions arrive at the detector at different times due to different velocities. Time of flight is recorded and as each ion hits the detector is gains an electron, generating a current, the size of which is proportional to the number of each type of ion.
- Data analysis: signal from detector passed to computer which generates a mass spectrum
what are the 2 methods of ionisation in a mass spectrometer?
electrospray or electron impact ionisation
describe the process of electrospray ionisation
- sample X is dissolved in a volatile solvent (water or methanol)
- sample X is injected through a hypodermic needle to produce a fine mist (aerosol)
- tip of the needle is attached to the positive terminal of a high voltage power supply
- particles are ionised by gaining a proton (H+ ion) from the solvent as they leave the needle
- this produces XH+ ions (ions with a single positive charge and a mass of Mr + 1)
- solvent evaporates while XH+ ions are attracted towards negative plate where they are accelerated
describe the process of electron impact ionisation
- sample being analysed is vapourised
- high energy electrons are fired at sample from an electron gun (hot wire filament with a current running through it which emits electrons)
- high energy electrons knock one electron off each particle, forming a 1+ ion
- 1+ ions are then attracted towards a negative electric plate where they are accelerated
what type of element/substance is electron impact ionisation used for and why?
- electron impact ionisation is used for elements/substances with low formula mass
- 1+ ion formed is known as a molecular ion; molecular ion often breaks down into smaller fragments, some of which are also detected in the mass spectrum
what type of element/substance is electrospray ionisation used for and why?
electrospray ionisation is used for substances with higher molecular mass as fragmentation rarely takes place
how do ions separate in the TOF mass spectrometer?
Once accelerated, all ions have same kinetic energy, though they will travel through flight tube at different velocities and reach detector at different times.
