Structure and Bonding Flashcards
Physical
What is the relative charge / mass of a proton?
+1, 1
What is the relative charge/mass of a neutron?
0, 1
What is the relative charge/mass of an electron?
-1, 1/1840
Name the properties of the nucleus:
- very small
- most of the mass of the atom
- contains protons and neutrons (therefor positively charged)
What is an ion?
An ion is an atom with a different number of electrons and protons
Give examples of 1+ ions:
- Group 1 ions (Li , Na, K)
- H
- NH4
Give examples of 2+ ions:
- Group 2 ions
- Zn
Give examples of 3+ ions:
- Group 3 ions
Give examples of 1- ions:
- Group 7 ions
- OH
- NO3
- H (hydride)
- HCO3
Give examples of 2- ions:
- Group 6 ions
- SO4
- CO3
Give examples of 3- ions:
PO4
What is an isotope?
An element with the same number of protons but a different number of neutrons
History of the atom - 1803
John Dalton - atoms are spheres and each element is made up of different spheres
History of the atom - 1897
J.J Thompson - discovered the electrons (and therefore that the atom wasn’t solid and was made up of other particles.
NOTE - developed the plum -pudding model (positive pudding)
History of the atom - 1909
Ernest Rutherford - discovered the nucleus through the gold leaf experiment
- also discovered the nucleus was very small and positively charged and that most of the atom was mainly empty space and that electrons were negative clouds
What was the gold leaf experiment?
- positive alpha particles fired at thin gold leaf
- most went through the gold leaf (mainly empty space)
- some were deflected back (they hit the positive nucleus)
History of the atom - 1913
Niels Bohr- proposed that electrons were fixed in energy shells (otherwise atoms would collapse)
How did Bohr prove shells?
EM radiation was absorbed when electrons moved to higher energy shells.
It was emitted when electrons moved down to lower energy shells.
- couldn’t be explained with cloud model
History of the atom - today
We now know about sub shells
Name the four stages of mass spectrometry:
- Ionisation
- Acceleration
- Deflection
- Detection
What are the two different types of ionisation (stage one)?
- Electron impact (used for elements and low Mr Compounds)
- Electrospray ionisation (used for high Mr compounds (e.g. proteins))
What is the equation for electron impact?
X(g) -> X^+(g) + e^-
Describe electron impact:
- high energy electrons are fired at the sample from an electron gun
- this knocks off one electron from each atom/molecule to form 1+ ions
What is the equation for electrospray ionisation?
X(g) + H^+ (g) -> XH^+ (g)
Describe Electrospray ionisation:
- the sample is dissolved in a volatile solvent (e.g methanol, water) and injected through a fine hypodermic needle as a fine spray into a vacuum in the ionisation chamber
- a very high voltage is applied to the end of the needle where the spray emerges (the needle is +vely charged)
- the particles gain a proton and become ions as a fine mist
- the solvent evaporates leaving 1+ ions
Describe acceleration:
The ions are accelerated using an electric field so that all the ions have the same kinetic energy.
Describe deflection:
- the ions then enter the flight tube
- ions with different masses have a different time of flight
- the lighter ions travel faster and take less time to reach the detector .
t = d x (m/(2KE))^(1/2)
Describe detection:
- the detector is a negatively charged plate - a current is produced when the ions hit the plate (the more ions that hit the plate, the larger the current)
- the mass of the ions can be calculated using the time of flight
What is a mass spectrum?
It is a graph that shows the number of particles (abundance) of each mass that hit the detector
NOTE:
- x- axis = m/z but as the charge of the particles is usually 1, the m/z ratio is basically the mass
- Generally the main peak is at Mr +1 (so minus 1 from the main peak)
- if abundance is measured in %, isotopes must add to 100%
Relative Atomic Mass:
The average mass of an atom of an element when measured on a scale on which the mass of an atom of 12C is exactly 12
Relative Molecular Mass:
The average mass of a molecule when measured on a scale on which the mass of an atom of 12C is exactly 12
Relative Isotopic Mass:
The mass of an atom of an isotope of an element on scale on which the mass of an atom of 12C is exactly 12
What is the order of sub shells?
s,p,d,f
S sub shell:
How many orbitals are there?
How many electrons can it hold?
Orbitals: 1
Electrons: 2
P sub shell:
How many orbitals are there?
How many electrons can it hold?
Orbitals: 3
Electrons: 6
D sub shell:
How many orbitals are there?
How many electrons can it hold?
Orbitals: 5
Electrons: 10
F sub shell:
How many orbitals are there?
How many electrons can it hold?
Orbitals: 7
Electrons: 14
Shell number vs Sub shells:
Shell Number: 1
Sub shells: 1s
Shell Number: 1
Sub shells: 2s, 2p
Shell Number: 1
Sub shells: 3s, 3p, 3d
What is the electron configuration of Iron (26 electrons)?
1s^2, 2s^2, 2p^6, 3s^2, 3p^6, 4s^2, 3d^6
NOTE:
- 4s filled before 3d
- this can also be written as
[Ar] 4s^2, 3d^6
- you fill orbitals singly first then pair up (due to electron repulsion)
Two special cases of electron configuration:
Cu - fill the 3d and leave the 4s as 4s^1 (not full)
Cr - fill the 3d halfway and leave the 4s as 4s^1 (not full)
THIS IS BC IT IS MORE STABLE!!
What is the Aufbau principle?
Electrons always enter the lowest energy orbital available
What is Hunds rule?
Electrons prefer their own orbital
How is the electron configuration of transition metal ions different?
They loose electrons from the 4s orbital first
What is ionisation energy?
The minimum amount of energy required to remove 1 mole of electrons from 1 mole of atoms in the gaseous state.
NOTE:
- always endothermic (requires energy)
- always +ve
How does shielding affect ionisation energy?
If there are more electron shells between the positive nucleus and negative electron that is being removed, less energy is required. There is a weaker attraction
How does atomic size affect ionisation energy?
The bigger the atom, the further way the outer electron from the nucleus. Therefore, the attractive forces between the nucleus and electron reduce and less energy is required. This makes it easier to remove electrons.
How does nuclear charge affect ionisation energy?
The more protons in the nucleus, the more positively charged the nucleus and therefore the bigger the attraction between the nucleus and outer electrons. This means more energy is required to remove the electron.
What is the removal of more than one electron from the same atom called?
Successive ionisation
Why are there jumps in graphs showing successive ionisation?
A jump in energy generally suggests electrons are being removed from the next shell (closer to the nucleus)
1st Ionisation trends - Groups:
Ionisation energy decreases as you go down the group:
- atomic radius increases as you go down the group meaning the outer electrons are further from the nucleus and the attractive force is weaker. Therefore, energy required to remove an electron decreases
- shielding increases as you go down the group - more shells between the nucleus and outer shell - attractive force is weaker - energy required to remove an electron decreases
NOTE:
proves Bohr & shells
1st Ionisation trends - Periods:
Ionisation energy increases across a period:
- as you go across a period the number of protons increases which in turn increases the nuclear attraction
- shielding is similar and distance from nucleus marginally decreases
- more energy is required to remove outer electron so ionisation energy increases
Exceptions in ionisation trends (in periods):
Aluminium
- the outer most electron in aluminium sits in a higher energy sub shell slightly further away from the nucleus than the outer electron in magnesium
- this means less energy is required to remove it (more shielding and greater atomic radius)
Sulphur
- evidence for electron repulsion - electrons repel each other so less energy is required to remove an electron from an orbital with 2 in than one with 1 in
- phosphorus and sulphur have the same amount of shielding (both have 3p orbital)
NOTE: the atomic model that Bohr came up with didn’t explain this
