Atomic structure Flashcards
what do the chemical properties of elements depend on?
Their atomic structure and electron arrangement
list the fundamental particles in an atom
Protons, neutrons and electrons
state the relative charges of each fundamental particle
- Proton = +1
- Neutron = 0
- Electron = -1
state the relative mass of each fundamental particle
- Proton = 1
- Neutron = 1
- Electron = 1/1836
Explain the relative mass of electrons
Electron mass is negligible
how do you calculate the number of neutrons
neutron = mass number - proton munber
define mass number
Mass number is the total sum of protons and neutrons in an atom
what does (+) and (-) mean on an element
+ means loss of electrons
- means gaining of electrons
list two discoveries from the gold foil experiment
- Atoms are mainly empty space
- Atoms have a small positive nucleus
State two differences between the plum pudding model and atomic structure today
- The nucleus contains both protons and neutrons
- Electrons are in orbitals
What is an isotope and why do all isotopes have the same chemical properties?
An isotope is an element with the same atomic number but different mass numbers. They have the same chemical properties due to the same electronic configuration
A mass number of an element should be written to how many decimal places?
One decimal place
State two elements exempted from the trend of electronic configurations in transition metals
Chromium and copper
write the electronic configuration for chromium
1s2 2s2 2p6 3s2 3p6 4s1 3d5
write the shorthand electronic configuration for scandium
[Ar] 4s2 3d1
What is the rule for transition metals when charged
Start removing electrons from 4s orbital because it the highest
Define ionization energy
The amount of energy required to remove one mole of an electron from one mole of an atom in its gaseous state
State 3 factors affecting ionization energies
- Atomic radius
- Electron shielding
- Number of protons (Nuclear charge)
Define atomic radius in terms of ionization energies
- The further away from the nucleus, the weaker the attraction for the outermost electron
Define number of protons in terms of ionization energies
The higher the nuclear charge (with an increasing number of protons) the greater the attraction
Define electron shielding
The repulsion of inner shells of electrons
Describe the trend of electron shielding
shielding remains constant across the period and increases down the group
Describe the trend of ionization energies in the periodic table
Ionization energy increases across the period and decreases down the group
Give the formula of first, second, and third ionization energies
• 1st = E(g) -> E+(g) + E-
• 2nd = E+(g) -> E2+(g) + E-
• 3rd = E2+(g) -> E3+(g) + E-
Why does protons and electrons matter when answering questions about ionization energies
Because two elements can be in the same group and have the same trend but both will have different number of electrons e.g carbon and silicon
Name one exemption from the trend of FIRST ionization energies and why
•Aluminum
• Aluminum electron in 3p orbital
• Magnesium electron in 3s orbital
• 3p is higher in energy than 3s
• Therefore outermost electron will be easier to remove due to weaker attraction
Name the second exemption from the trend of FIRST ionization energies
• Sulfur
• Sulfur electron from orbital with two electrons
• Phosphorus electron from orbital with one electron
• More electrons lead to repulsion
Therefore making it easier to remove outermost electron
What is the function of a mass spectrometer
To determine the relative isotopic mass and abundance of isotopes
What does ToF mean?
Time of flight
Explain the time of flight technique
• Particles of a substance are ionized to form 1+ ions which are accelerated so they all have the same KINETIC ENERGY
How is the mass of each ion determined?
The time taken to travel a fixed distance
Why is this process carried out in a vacuum?
Because it would otherwise be slowed down by air particles
State the unit of mass, distance, time, velocity, and energy
Kg, m3, s, ms-1, J
Describe electron impact
• The gaseous sample is bombarded with high energy electrons
• From an ELECTRON GUN
• knocks off an electron from each particle forming a 1+ ion
E.g Na+(g) -> Na2+ (g) + E-
Describe electro spray ionization
• The compound is dissolved in a volatile solvent
• The solution is injected through a hypodermic needle which is highly positively charged
• The sample molecule M, gains a proton forming MH+
E.g M(g) + H+ -> MH+(g)
How are positive electrons accelerated? And why?
Using an electric field, so they all have the same kinetic energy
What does the velocity for each electron depend on?
It’s mass
Which particles travel faster and which travel slower
Lighter particles travel faster and heavy particles travel slower
Give the formula for the stage 2 acceleration
K.E = 1/2 mv2
Rearrange the formula to make v the subject
V= root 2xK.E / m
Where do positive ions travel to? And what is this called?
Into a tube, Ion drift
Give the formula for velocity
V= d/t
Give the formula for d
D= T x root 2xK.E/ m
Give the formula for T
T= d x root m/ 2xK.E
Give the formula for M
M = 2 x K.E x t2/d2
What happened when positive ions hit the detector?
The positive ions are discharged by gaining electrons from the plate
Hence an electric current is measured
How is abundance of an isotope measured?
The higher the abundance of an isotope, the larger the current
why are ions accelerated by an electric plate?
To produce high speed electrons
how many orbitals or shells do electrons contain?
1s 2p 3s 3p 4s 3d
how many orbitals and electrons do shells contain?
1s- 1 orbital, two electrons
2p- 3 orbitals, six electrons
3s- 1 orbital, two electrons
3d- 5 orbitals, ten electrons
4s- 1 orbital, two electrons
does 4s or 3d have a higher energy?
3d
what would be the relationship between two electrons in the same orbital in terms of their spin?
They have an opposite spin, repel each other because they are both negative
when would you use a different types of ionisation in a mass spectrometry?
electron impact is used for organic and inorganic molecules with a low formula mass.
electrospray is used for substances with a higher molecular mass including biological molecules. e.g. proteins
Describe how a time of flight mass spectrometer works?
Ionisation- ionised to become positively charged
Acceleration- Positive ions attracted towards negatively charged plate
Ion Drift- ions pass through a hole in plate, form a beam with constant kinetic energy, travel along tube to the detector. time of flight is therefore directly proportional to the square root of mass.
Detection- Positive ions pick up electrons, current flows, m/z value and time of flight is recorded. largest current from most abundant ions.
Give two reasons why it is necessary to ionize the isotopes of chromium before they can be analyzed in a TOF mass spectrometer
• Ions will interact with and be accelerated by an electric field
• Ions create a current when hitting the detector
Why does silicon have a lower second ionisation energy than aluminium
The second ionisation of silicon is lower than that of aluminium because the electrons in the outermost energy level of silicon are more shielded by the inner electrons than the electrons in the outermost energy level of aluminium.
This is due to the fact that silicon has a large atomic radius than aluminium which means that the outermost shell in silicon is farther away from the positively charged nucleus and shielded by the inner electrons. Additionally, silicon as more electrons than aluminium which also contributes to the greater shielding effect.
Explain why the atomic radius decreases across Period 3, from sodium to chlorine
• Nuclear charge increases
• Shielding is similar/ same or electrons added to the same shell
