1. Atomic Structure Flashcards
3 factors of the Bohr Model:
- protons + neutrons are found in the centre of the atom called the nucleus
- protons + neutrons can also be called nucleons
- electrons orbit around the nucleus in shells/energy levels
Name Fundamental Particles of an Atoms, their relatives masses and relative charges
Atomic Number is equal to what
equal to the number of protons
Mass Number is equal to what
equal to the sum of the number of protons and neutrons
What are isotopes
Atoms with the same number of protons but different number of neutrons
Why do isotopes of the same element have the same chemical properties?
They have the same electronic configuration
Isotopes have the same electron configuration so …
They have the same chemical properties
Number of Neutrons =
Mass Number - Atomic Number
Atoms have a neutral charge, why?
Number of protons = Number of electrons
What are cations?
An atoms that has lost electrons so protons>electrons and is now an ion
What are anions?
An atom that has gained electrons so electrons>protons and is now an ion
1st Ionisation Energy:
the amount of energy needed to remove a mole of e- from a mole of atoms, in the gaseous state (units= kJ mol-1
Equation for the 1st ionisation energy (of Potassium, K):
K(g) → K+ (g) + e-
1st 3 Ionisation Energies of Boron:
1: B(g) → B+ (g) + e-
2: B+(g) → B 2+ (g) + e-
3: B 2+(g) → B 3+ (g) + e-
3 factors that influence I.E:
1) Shielding
2) Nuclear Charge (number of protons in the nucleus)
3) Distance from nucleus
Trend in 1st I.Es of elements down a group:
- Shielding increases
(- Distance from nucleus increases) - Weaker attraction between nucleus and outermost e-
- 1st I.E decreases down group
Why do I.Es 1-3 increase?
Each e- is being removed from a more +ve ion each time. (attraction between the electrons and the protons increase as there are less electrons being attracted by the same number of protons)
Why does the 4th I.E increase drastically?
The 4th e- being removed from a shell closer to the nucleus and a more positive ion and so is much more strongly attracted to the nucleus
The following data shows the first seven successive ionisation energies of a period 3 element. State which element it is and explain your reasoning.
(Calculate gap between each e- removed)
- Largest increase between 4th + 5th I.Es
- 5th e- is on the shell closer to the nucleus
- Element must have 4 e- on its outer shell
- Period 3, Group 4 = Silicon
Why is Li a bigger atoms than Be?
- Same shielding
- Be has more protons
- so, stronger attraction to the outer e-
Why is Li a bigger atoms than He?
- Li has an extra shell
- Li’s outermost e- is further away from the nucleus
- Outer e- is more shielded
- Outer e- less strongly attracted to the nucleous
Which element has the highest 1st I.e of all the elements?
He. Because it has same shielding as H but more protons than H.
Trend in 1st I.E across a period:
(use example of Period 3 to explain)
- General increase
- Same shielding, grater number of protons, stronger attraction between nucleus and outermost e-
- with 2 exceptions
Reasons for the exceptions - P subshell lower in energy than than the S subshell → less energy required to remove the e-
- 1st e- removed from P = 1p subshell + unpaired. 1st e- removed from S = 1p subshell + paired. P= lower I.E due to e- pair repulsion. Therefore, less energy needed to remove the e- from S.
Why does the atomic radius get smaller across the period?
- same shielding
- number of protons increases
- greater attraction between nucleus and electrons
What 2 factors does the mass spectrometer measure?
1) relative abundance
2) mass/charge (m/z) ratio
Name the different parts of the mass spectrometer:
Why is the inside of the mass spectrometer a vacuum?
To prevent any of the particles being tested from colliding with molecules from the air
Name the 2 ionisation methods
1) electron impact
2) electrospray
Describe the acceleration step in mass spectrometry?
+ve ions attracted towards the -vely charged plate and accelerate towards it. amount of acceleration depends on the m/z ratio. High m/z ratio ions will accelerate slower than low m/z ratio ions. Once accelerated, all ions will have the same KE
Describe ion drift in mass spectrometry
Some ions pass through the hole in -vely charged plate, & travel along the flight tube towards detector. Travel at diff speeds = drift apart.
Describe detection in mass spectrometry
ions arrive at detector at diff time due to diff velocities. ‘Time of flight’ recorded as each ion hits detector and gains an e-, which generates a current, the size of which is proportional to the abundance of each type of ion
Describe data analysis in mass spectrometry
the signal from the detector is passed to a computer which generates an electric current
Why are sample particles ionised?
1) so they can accelerate towards the negatively charged plate
2) so they can generate a current when they hit the detector
How is the ion accelerated?
1) +ve ion attracted towards the -vely charged plate
2) all ions have the same KE
How are ions separated in the flight tube?
Low m/z ions travel at higher speeds + move ahead of those travelling more slowly (high m/z)
How are ions detected?
- each ion hits the detector
- ion gains an e-
- generate a current
- size of current is proportional to the abundance of the ion
How do you find the mass from a m/z ratio?
M/Z value - 1 (1=charge)
Describe electrospray ionisation as a method of ionisation:
- sample is dissolved in a volatile solvent
- sample is injected through a hypodermic needle at a high voltage, producing a fine mist
- sample is ionised by gaining a proton
Give an example equation for electrospray ionisation:
(H+ = proton)
X + H+ → XH+
Describe electron imoact as a method of ionisation:
- sample is vapourised
- high energy e- are fired at sample
- from an e- gun
- 1 e- is knocke doff each particle
Give an example equation for electron impact:
X (g) → X+ (g) + e-
Ar equation
KE equation
KE = 1/2 mv^2
Equation to work ou the mass of 1 atom of an element:
(in kg)
convert the Mr to kg mol^-1 by ÷1000
then divide this by Avagadro’s constant
Molecular Ion Peaks for e- impact
What is the peak with the largest m/z value called?
What is the peak with an m/z of 15 caused by?
- peak with largest m/z ratio called the ‘Molecular Ion’ peak
- fragment caused by +CH3 ion
What is the m/z ratio of the molecular ion equal to?
the Mr of the whole molecule
Find the relative abundances of isotopes of Br2
Exist as 79Br and 81Br isotopes. 50% abundance of each
1:2:1
