atomic structure

arrangement of subatomic particles

Protons and neutrons are in the nucleus - nucleons. 

They are held together by a strong nuclear force. 

Electrons surround the nucleus in orbitals. 

They are held in the atom by electrostatic forces between protons and electrons. 

Nuclear force is much stronger than electrostatic force. 

mass number

Total number of protons + neutrons in the nucleus

atomic number

The number of protons in the nucleus

RELATIVE ATOMIC MASS [A_r] 

the average mass of an atom of an atom of an element, taking into account its naturally occurring isotopes, relative to 1/12^th the mass of an atom of carbon-12.

equation for Ar

A_r = (isotope mass number x % abundance) + (isotope mass number x % abundance) 

Sum of % isotope abundance 

RELATIVE ISOTOPIC MASS 

mass of an atom of an isotope relative to 1/12^th the mass of an atom of carbon-12. Always a whole number. 

RELATIVE MOLECULAR MASS [M_r] 

average mass of a molecule in relation to 1/12 the mass of a carbon 12 atom. 

isotopes

An isotope is an atom of the same element with the same number of protons (atomic number) and a different number of neutrons (so different mass number). 

Same chemical properties as they have the same electron configuration. 

electron impact ionisation

• Sample is vaporised then high energy electrons are fired at the sample using an electron gun, one electron is knocked off each atom/particle forming a 1+ ion. 

• X_(g) → (X)⁺_(g) + e^- 

electrospray ionisation

• Sample is dissolved in a volatile solvent and is injected into the ionisation chamber through a hypodermic needle which has a high voltage as is positively charged. The particles gain a proton and become 1+ ions as a fine mist. The solvent evaporates leaving the 1+ ions. 

X_(g) + H⁺ → (XH)⁺_(g)

ACCELERATION 

Ions are accelerated using an electric field.

The positively charged ions accelerate towards a negatively charged plate.

This is so that all the ions have the same kinetic energy.

They all have the same kinetic energy but their velocity will differ as it depends on their mass, lighter ions will have a higher velocity than heavier ions

ION DRIFT 

Ions pass through a hole in the plate into the flight tube where they enter a region with no electric field so they just drift through it towards the detector. Ions with different masses have a different time of flight. 

DETECTION

The detector is a negatively charged plate and a current is produced when the ions hit the plate. The positive ions pick up an electron from the detector, causing a current to flow. 

CHROMIUM 

Expect it to be 4s² 3d⁴ however, it donates one of its 4s electrons to the 3d subshell so the 3d subshell is more stable as it is half-full. Its configuration is actually: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵

COPPER 

Expect it to be 4s² 3d⁹ however, it donates one of its 4s electrons to the 3d subshell so the 3d subshell is more stable as it is now full. Its configuration is actually: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d¹⁰

First ionisation energy

The energy needed to remove 1 electron from each atom of an element in one mole of gaseous atoms to form one mole of gaseous ions with a 1+ charge.

Second ionisation energy

The energy needed to remove 1 electron from each ion of an element in 1 mole of gaseous +1 ions to form 1 mole of gaseous ions with a +2 charge

factors affecting ionisation energy

atomic radius

nuclear charge 

shielding 

atomic radius

The smaller the atomic radius, the higher the first ionisation energy. 

This is because the outer electron is more strongly attracted to the nucleus

nuclear charge

The higher nuclear charge, the higher the first ionisation energy. 

This is because a higher nuclear charge means a smaller atomic radius 

Because there are more protons to attract the outer electrons 

Therefore more attracted to the nucleus 

shielding

The more shielding, the lower the first ionisation energy 

Inner shells repel the outer electrons making them easier to lose

ionisation energy across a period

Higher nuclear charge, smaller atomic radius. 

Outer electrons are more attracted to the nucleus. 

Shielding is constant.

ionisation energy down a group

Larger atomic radius. 

Increase in shielding as more energy levels are added. 

Outer electron is less attracted to the nucleus and is therefore easier to lose. 

exceptions group 2 - 3

Dip in first ionisation energy. 

Move to a new energy level with higher energy. S → P subshell

Further away from the nucleus and more shielding. 

exceptions group 5 - 6

Dip in first ionisation energy. 

In group 5, p subshell has one electron in each orbital, no repulsion. 

In group 6, p subshell has one orbital with 2 electrons in. 

The electrons in the same orbital repel each other. 

So less energy is needed to remove the outer electron. 

successive ionisation energies 

Successive ionisation energies means that more and more electrons are removed, each from an ion that is becoming increasingly positive.

successive ionisation energies between shells

Each time a new shell is broken into, there is a sudden rise in ionisation energy. For example, for sodium, which has one outer electron, there is a big jump in ionisation from the first to second. This is because the second electron is being removed from a shell that is much closer to the nucleus, meaning there is stronger attraction from the nucleus.

Successive ionisation energies increase within each shell

Each time an electron is removed, even if you haven’t broken into a new inner shell, the ionisation energy increases because you are removing an electron from an increasingly positive ion. For example, for magnesium, which has two outer electrons, the second ionisation energy is greater than the first, because it is harder to remove an electron from an Mg2+ ion than an Mg+ atom, because there is a stronger attraction back.