Atomic structure 3.1.1 Flashcards
(25 cards)
Why does atomic radius decrease down a period
electrons are being added to the energy level at the same time that the nucleus is gaining a proton
So, there is an increase in nuclear charge attracting the electrons more strongly pulling them closer to the positive nucleus
Why does atomic radius increase down a group
The amount of energy levels increases
The inner electrons repel the outer electrons from the positive nucleus so they’re held further away
First ionisation energies in group 2
Ionisation energy increases down the group as each element going down has an extra electron shell so outer electrons are further away from the nucleus so there is less nuclear attraction
What are the trends observed in ionisation energies across period 3?
There is an increase going across period 3 because there is a higher nuclear charge (which requires a lot of energy to overcome) and the same amount of shielding
There is a dip at aluminium because the outer electron is in a p-subshell so is higher in energy so less energy is required to remove it
There is a dip at sulfur due to electron paired repulsion (the electrons spin opposite directions and repel each other)
What general trend is observed in ionisation energies across period 3?
There is an increase in ionisation energies due to a higher nuclear charge and the same amount of shielding.
Why is there a dip in ionisation energy at aluminium in period 3?
The outer electron is in a p-subshell, which is higher in energy, requiring less energy to remove it.
What causes the dip in ionisation energy at sulfur in period 3?
The dip is due to electron paired repulsion, as the electrons in the same orbital repel each other.
What is the first ionisation energy?
The energy required to remove one electron (outermost) from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions.
M(g) -> M(g)+ + e-
Transition metal
element that has an incomplete d-sub level either in the elemental state or as an ion
Second ionisation energy
Energy required to remove 1 electron from each ion in one mole of gaseous 1+ ions to form a mole of 2+ gaseous ions
M(g)+ –> M(g)2+ +e-
Electron configurations
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d
S= 2e-
P=6e-
D=10e-
F=14e-
☆Only fill 3d when 4s is completely full HOWEVER, once 3d starts to fill, 4s goes on the outside and empties first
EXEPTIONS
Cr → [Ar] 3d⁴ 4s² 3d⁵ 4s¹
Cu → [Ar] 3d¹⁰ 4s¹
Why is a mass spectrometry useful
-to find the mass and abundance of each isotope in an element
-determine relative atomic mass
-help identify molecules by determining relative molecular mass
-test atheletes blood/urine for drugs
-analyse atmospheric samples
Mass Spectrometry
1: IONISATION
electron impact
-sample is vapourised (g)
-high energy electron fired at it from the electron gun (hot wire filament)
- electron removed from the outer shell of the atom/molecule
M(g) → M⁺ + e⁻
⋆for elements
⋆ molecules with a low Mr
⋆molecules are broken into fragments
mass spectrometry
electrospray ionisation
-Sample is dissolved in a volatile solvent (methanol)
-injected trough a thin hypodermic needle which is attached to the positive terminal of a high voltage power supply
-the particles are ionised by gaining a proton from the solvent as they leave the needle
M(g) + H⁺ → MH⁺ (g)
⋆high molecular mass
⋆no fragmentation
mass spectrometry
acceleration
positive ions are accelerated using an electric field so they have the same kinetic energy
KE= 1/2 mv²
speed = V=√2KE/m
⋆As all particles have the same kinetic energy, the speed depends on its mass
What does the speed on a particle depend in in mass spectrometry
Mass
equation for kinetic energy
KE= 1/2 mv²
MASS SPECTROMETRY
ion drift
Positive ions travel through a hole in the negatively charged plate and then into a tube
- the time of flight of each particle through the tube depends on its speed (t=d/v) d=length of tube
ToF= d√m/KE
⋆Lighter ions reach the detector first
Time of flight equation
time = d * square root of ( mass/2 * kinetic energy)
Mass spectrometry
detection
At the end of the tube, the positive ions strike a negatively charged plate and gain an electron to neutralise
This generates a flow of electrons which is amplified to produce a signal on a computer
The relative intensity of the peak produced by an ion is proportional to the magnitude of the amplified current
current or peak of light = abundance of ion
⋆ELECTROSPRAY -> m/z = Mr + 1 so -1 to find m/z
John Dalton
1803; Atomic Theory: all matter made of atoms;
all atoms of an element are alike, but are different from other elements;
elements can be combined to make compounds;
chemical reactions are a rearrangement of elements, but do not change the elements themselves.
J.J Thomson
1897 discovered the electron and proposed plum pudding model
Earnest rutherford
(1911) Gold foil experiment. Said the atom is mostly empty space. Discovered the nucleus.
James Chadwick
1932-Discovered the neutron