Save My Rxams Atomic Dtructure Flashcards
Atom structure
mostly made up of empty space around a very small, dense nucleus that contains protons and neutrons
Nucleus charge
overall positive charge
The protons have a positive charge and the neutrons have a neutral charge
Where electrons are found
Negatively charged electrons are found in orbitals in the empty space around the nucleus
Proton mass
1
Neutron mass
1
Electron mass
1/1836
Proton relative charge
+1
Neutron relative charge
0
Electron charge
-1
Atomic number
is the number of protons in the nucleus of an atom and has symbol Z
equal to the number of electrons present
mass number
is the total number of protons and neutrons in the nucleus of an atom and has symbol A
number of neutrons can be calculated by:
mass number - atomic number
what holds an atom together
electrostatic attraction between the positive nucleus and negatively charged electrons orbiting
Atom charge
neutral and has no overall charge
all atoms and ions of the same element have
the same number of protons
Diff neutron
Isotopes
atoms of the same element that contain the same number of protons and electrons but a different number of neutrons
same chemical properties but different physical properties
Chemical properties of isotope
display the same chemical characteristics
This is because they have the same number of electrons in their outer shells
Physical properties of an isotope
difference between isotopes is the number of neutrons
isotopes have different physical properties such as small differences in their mass and density
What Tof is used for
accurate determination of the relative atomic mass of an element, based on the abundance and mass of each of its isotopes
4 key stages in time of flight mass spectrometry:
Ionisation
Acceleration
Ion drift
Detection
1: Ionisation
Electron Impact (or electron ionisation)
Electrospray Ionisation
Electron Impact Ionisation
substances which have a lower molecular mass
vaporised and then bombarded with high energy electrons
a hot wire filament which emits electrons as a current runs through it
electron is knocked off each particle, forming a 1+ ion
Electrospray Ionisation
dissolved in a volatile solvent
The solvent is injected into the mass spectrometer using a hypodermic needle
This produces a fine mist or aerosol
The needle is attached to a high voltage power supply, so as the sample is injected, the particles are ionised by gaining a proton from the solvent
Equation for electro spray
X (g) + H+ → XH+ (g)
Acceleration
accelerated using an electric field
They are all accelerated to have the same kinetic energy
Lighter ions will move faster and heavier ions will move slower
Ion Drift
1+ ions will pass through a hole in the negatively charged plate and move into a flight tube
Detection
the 1+ ions will hit a negatively charged ‘detector’ plate
As they hit this electric plate, they gain an electron
This gaining of an electron discharges the ion, and causes a current to be produced
This size of the current is proportional to the abundance of those ions hitting the plate and gaining an electron
The detector plate is connected to a computer, which produces the mass spectrum
time of flight is proportional to
the square root of the mass of the ions, showing that the lighter the ion the faster it will pass through and the quicker it will hit the detector.
electron configuration
The arrangement of electrons in an atom
Principal quantum numbers
N
used to number the energy levels or quantum shells
The lower the principal quantum number, the closer the shell is to the nucleus
n = 1 : up to
2 electrons
n = 2 : up to
8 electrons
n = 3 : up to
18 electrons
n = 4 : up to
32 electrons
Subshell letters
S
P
D
F
Orbitals
Subshells contain one or more atomic orbitals
S orbital shape
spherical in shape
The size of the s orbitals increases with increasing shell number
p orbital shape
a dumbbell shape
Ground state
most stable electronic configuration of an atom which has the lowest amount of energy
This is achieved by filling the subshells of energy with the lowest energy first
block elements
Have their valence electron(s) in
an s orbital
4s orbital is filled before
the 3d orbital
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
kilojoules per mole (kJ mol-1)
first ionisation energy
the energy required to remove one mole of electrons from one mole of atoms of an element to form one mole of 1+ ions
size of the first ionisation energy is affected by four factors:
Size of the nuclear charge
Distance of outer electrons from the nucleus
Shielding effect of inner electrons
Spin-pair repulsion
Ionisation energy across a period
Across a period the nuclear charge increases
This causes the atomic radius of the atoms to decrease, as the outer shell is pulled closer to the nucleus, so the distance between the nucleus and the outer electrons decreases
The shielding by inner shell electrons remain reasonably constant as electrons are being added to the same shell
It becomes harder to remove an electron as you move across a period; more energy is needed
Dips in the trend
between beryllium and boron as the fifth electron in boron is in the 2p subshell, which is further away from the nucleus than the 2s subshell of beryllium
From one period to the next
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
Ionisation energy down a group
The number of protons in the atom is increased, so the nuclear charge increases
But, the atomic radius of the atoms increases as you are adding more shells of electrons, making the atoms bigger
So, the distance between the nucleus and outer electron increases as you descend the group
The shielding by inner shell electrons increases as there are more shells of electrons
These factors outweigh the increased nuclear charge, meaning it becomes easier to remove the outer electron as you descend a group
So, the ionisation energy decreases
Successive ionisation energies of an element
increase
Removing an electron from a positive ion is more difficult than from a neutral atom
attractive forces increase due to decreasing shielding and an increase in the proton to electron ratio
First electron easy to remove
easily removed from the atom due to the spin-pair repulsion of the electrons in the 4s orbital
Second electron. Ore diffulcukt
more difficult to remove than the first electron as there is no spin-pair repulsion
Successive ionisation data can be used to:
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
