Physical Unit 1.1: Atomic Structure Flashcards
what is the structure of atoms in terms of protons, neutrons & electrons?
atoms have a central nucleus containing protons & neutrons
most of the atom’s mass is concentrated in the nucleus
the diameter nucleus is tiny compared to the whole atom
electrons orbit the nucleus in energy levels/orbitals
orbitals take up most of the atom’s volume
atoms have no charge
what is the relative mass & charge of protons, neutrons & electrons?
protons:
relative mass 1
relative charge +1
neutrons:
relative mass 1
relative charge 0
electrons:
relative mass 1/1836 (0.005)
relative charge -1
define ion
has a different number of electrons to protons
has a charge
define atomic number
number of protons
define mass number
number of protons + neutrons
define isotope
atoms with the same number of protons & different number of neutrons
(= atoms of the same element with same atomic number & different mass number)
what determines the chemical properties of an element?
number & arrangement of electrons
how do the chemical & physical properties of different isotopes compare?
isotopes have the same configuration of electrons so have the same chemical properties
isotopes have slightly different physical properties because they depend on the mass of the atom
define relative atomic mass
the average mass of atoms of an element relative to 1/12th the mass of a 12C atom
define relative isotopic mass
the average mass of atoms of an isotope of an element relative to 1/12th the mass of a 12C atom
define relative molecular mass
the average mass of a molecule relative to 1/12th the mass of a 12C atom
how does a time of flight mass spectrometer work?
- ionisation
- acceleration of ions
- ion drift
- detection
explain ionisation in a mass spectrometer
electron impact - used for elements & low Mr compounds (smaller)
high energy electrons are fired at the sample from an electron gun
this knocks one electron off each atom/molecule to form 1+ ions
= particles lose an electron
electrospray ionisation - used for high Mr compounds (bigger)
sample is dissolved & injected through a needle at high pressure
a high voltage is applied to the end of the needle where spray is released
the particles gain a proton (H+ ion) as they leave the needle so they become ions
sample turns into a gas of 1+ ions
explain the acceleration of ions
positively charged ions are accelerated by an electric field so all ions have the same kinetic energy
explain ion drift
separation of ions
ions enter the flight tube
ions with different masses have a different time of flight
lighter ions have a higher velocity so take less time to reach the detector
explain detection
positive ions are attracted to the negatively charged detector
e- is transferred from detector to 1+ ion
& produces a current when they hit
the size of the current is proportional to the relative abundance
what is the main peak from electrospray ionisation?
Mr + 1
so must subtract 1 to find the Mr
how do you find the relative atomic/formula mass from mass spectrometer data?
mass/charge ratio on x-axis
relative abundance on y-axis
(abundance x mass)/total abundance
why are there peaks at different mass/charge values?
different isotopes
what can a smaller, lighter peak be?
caused by fragments
fragmentation can happen in electron impact ionisation but not electrospray
describe the periodic table trends for:
outer electron distance from nucleus
outer electron orbital
see periodic table in atomic structure booklet
how are electrons arranged?
in energy levels/shells
which have s, p & d sub-shells
which have orbitals
each orbital can hold 2 electrons that have opposite spins
as the number of the shells increases
distance from the nucleus increases
define orbital
the region of space that electrons are most likely to be in
how are electrons filled up?
electrons enter the lowest energy orbital available
so 4s generally fills up before 3d because it has less energy
electrons prefer to occupy orbitals on their own so only pair up when no empty orbitals of the same energy level are available
what electrons are lost to form ions?
electrons in the highest energy levels are lost first
electrons are lost from 4s before 3d because when electrons fill it, 4s goes above 3d
because smaller increase in the electron’s energy required to leave the atom
what is the electron configuration of Cr?
1s2 2s2 2p6 3s2 3p6 4s1 3d5
what is the electron configuration of Cu?
1s2 2s2 2p6 3s2 3p6 4s1 3d10
explain the electron configurations of Cr & Cu
4s1 3d5 & 4s1 3d10 are more stable than 4s2 3d4 & 4s2 3d9
3d lower energy?
define first ionisation energy
the energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions
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 gaseous 2+ ions
what is the equation for first ionisation energy?
X(g) –> X+(g) + e-
how does distance from the nucleus affect ionisation energy
distance from nucleus/atomic/ionic radius
the smaller the distance from the nucleus, the stronger the electrostatic attraction b/w the nucleus & outer electron
so more energy is needed to remove the outer electron
so the higher the ionisation energy
how does nuclear charge affect ionisation energy?
nuclear charge/number of protons
the greater the number of protons/the greater the nuclear charge, the stronger the attraction b/w the nucleus & outer electron
more energy is needed to remove the outer electron
so the higher the ionisation energy
how does shielding affect ionisation energy?
shielding - the # of shells b/w the nucleus & outer electron
the greater the shielding, the weaker the attraction b/w the outer electron & nucleus
less energy needed to remove the outer electron
so lower ionisation energy
what is the general trend in first ionisation energy down group 1?
ionisation energy decreases bc:
distance from nucleus increases
shielding increases (bc # of shells increases)
so weaker attraction b/w outer electron & nucleus
so less energy needed to remove e-
what is the general trend in first ionisation energy across period 3?
ionisation energy increases bc:
distance from nucleus decreases
nuclear charge increases
same shielding
what are the anomalies in the trend in ionisation energy across period 3 & explain them?
Al lower ionisation energy than Mg bc:
outer e- for Al is in a p orbital, which is higher in energy than the outer e- in an s orbital in Mg
so less increase in energy needed to remove it
S lower ionisation energy than P bc:
in sulfur, 2 e-s pair up in a p orbital
this causes repulsion b/w the pair of electrons (as they are both -vely charged)
so the electrons require less energy to be lost
this has less of a decrease than b/w Al & Mg
describe successive ionisation energies
successive ionisation energies increase because as e-s are removed, the e-s are pulled closer to nucleus so there is a stronger attraction b/w the remaining outer shell e-s & the nucleus
the largest difference in successive ionisation energies comes after the group # of the element
because more energy is required to remove an e- from a lower energy level (i.e. the next shell) e- as it is closer to & more strongly attracted to the nucleus
what is the formula linking mass, Ar & avogadro’s constant?
m = Ar x 10-3/Na
m1/t1^2 =
m2/t2^2
