1. Atomic Structure Flashcards by Sehar Nadeem

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

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Name Fundamental Particles of an Atoms, their relatives masses and relative charges

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Atomic Number is equal to what

equal to the number of protons

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Mass Number is equal to what

equal to the sum of the number of protons and neutrons

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What are isotopes

Atoms with the same number of protons but different number of neutrons

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Why do isotopes of the same element have the same chemical properties?

They have the same electronic configuration

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Isotopes have the same electron configuration so …

They have the same chemical properties

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Number of Neutrons =

Mass Number - Atomic Number

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Atoms have a neutral charge, why?

Number of protons = Number of electrons

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What are cations?

An atoms that has lost electrons so protons>electrons and is now an ion

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What are anions?

An atom that has gained electrons so electrons>protons and is now an ion

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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

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Equation for the 1st ionisation energy (of Potassium, K):

K(g) → K+ (g) + e-

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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-

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3 factors that influence I.E:

1) Shielding
2) Nuclear Charge (number of protons in the nucleus)
3) Distance from nucleus

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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

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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)

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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

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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