Atomic structure

What are isotopes?

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

Why do isotopes have the same chemical properties?

They have the same electron configuration

Why do isotopes have different physical properties?

Physical properties depend on atomic mass

Define relative isotopic mass

The mass of an isotope relative to 1/12th of the mass of an atom of carbon-12

Define relative atomic mass

The average mass of an atom of an element relative to 1/12th of the mass of an atom of carbon-12

Define relative molecular mass

The average mass of a molecule compared to one twelfth the mass of one atom of carbon-12.

How can you find the relative atomic mass/isotopic abundance of an element?

Using a time of flight mass spectrometer

What are the four stages of mass spectrometry?

Ionisation, acceleration, ion drift, detection

What are the two methods of ionising the sample in mass spectrometry?

Electrospray ionisation and electron impact ionisation

How does electrospray ionisation work?

• Sample is dissolved in a volatile solvent

• Injected through nozzle at high voltage

• Each particle gains a proton

How does electron impact ionisation work?

The sample is vaporised and an "electron gun" is used to fire high energy electrons at it, knocking an electron off each particle so they're all +1 ions.

How are the particles accelerated in time of flight mass spectrometry?

The positively charged ions are accelerated by an electric field so that they all have the same kinetic energy. (this means the lighter ions will be faster than the heavier ions)

How does ion drift work?

The ions enter a region without an electric field, so they just drift through it. Lighter ions will drift through faster than heavier ions.

Describe the detection stage

Lighter ions reach the detector quicker than the heavier ions as they're travelling faster in the drift region. The detector detects charged particles and a mass spectrum is produced.

How many orbitals are in the s sub shell?

1 orbital

How many orbitals are in the p sub shell?

3 orbitals

How many orbitals are in the d sub shell?

5 orbitals

How many orbitals are in the f sub shell?

7 orbitals

How many electrons are in each orbital?

2 electrons

What direction do the two electrons in an orbital spin?

In opposite directions - repel each other as both are negative

Why does the 4s orbital fill before the 3d orbital?

The 4s subshell has a lower energy level than the 3d subshell

Define the first ionisation energy

The energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions

What is ionisation energy measured in?

kJ mol-1

The lower the ionisation energy…

the easier it is to form an ion

Is ionisation endothermic or exothermic?

endothermic

Give an example of a 1st ionisation energy equation

X(g) → X⁺(g) + e⁻

What are the factors affecting ionisation energy?

Nuclear charge, Distance from the nucleus, Shielding

What does a high ionisation energy mean?

There's a high attraction between the electron and the nucleus and so more energy is needed to remove the electron

Does nuclear charge increase or decrease ionisation energy?

Increase - stronger attraction

Does distance from the nucleus increase or decrease ionisation energy?

Decrease - less attraction

Does shielding increase or decrease ionisation energy?

Decreases - less attraction

Why does ionisation energy increase across a period?

Increase in nuclear charge - more difficult to remove an electron

Why does ionisation energy decrease going down a group?

Due to increased atomic radius and shielding which reduces electrostatic forces of attraction

When do successive ionisation energies occur?

When further electrons are removed

Why do successive ionisation energies increase?

Each electron is being removed from a more positive ion so the attraction is greater, less repulsion.

Why is there a big increase in ionisation energy when the electron is being removed from a new shell?

electron is closer to the nucleus so stronger electrostatic attraction

Why does aluminium have a lower ionisation energy than magnesium?

The outer electron in aluminium is in a 3p orbital which has a slightly higher energy/further from the nucleus than the 3s orbital, therefore needs less energy to remove.

Why does sulfur have a lower ionisation energy than phosphorus?

In phosphorous, each of the three 3p orbitals contain just one electron, while in sulfur, one of the 3p orbitals must contain two electrons. The repulsion between the paired electrons makes it easier to remove one of them, despite the increase in nuclear charge.