Atomic Structure and Mass Spectrometry

These flashcards cover key concepts related to atomic structure, mass spectrometry, electronic structure, and ionisation energies, providing a comprehensive study tool for exam preparation.

What was the early model of the atom before the discovery of the electron?

Tiny spheres that could not be divided.

What did the plum-pudding model suggest?

The atom was a ball of positive charge with negative electrons embedded in it.

What experiment replaced the plum-pudding model with the nuclear model?

Rutherford’s alpha scattering experiment.

In the nuclear model, where is the mass of the atom concentrated?

In the nucleus.

What did Neils Bohr propose about electron orbits?

Electrons orbit the nucleus at specific distances and energy levels.

What does a mass spectrometer determine?

Isotopes present in a sample and to identify elements.

What is the first step of the mass spectrometer process?

Ionisation.

How does electron impact ionisation work?

A vaporised sample is injected at low pressure, and an electron gun firing high energy electrons knocks out an outer electron.

What does electron spray ionisation involve?

Dissolving the sample in a polar, volatile solvent. Inject through very fine needle giving a fine mist/aerosol. At the tip with high voltage, sample gains a proton. Solvent evaporates.

What is an isotope?

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

What affects the time of flight of ions in a mass spectrometer?

Their mass-to-charge (m/z) ratio.

What are the four steps in a mass spectrometer?

Ionisation, Acceleration, Flight Tube, Detection.

What does the ion drift area in a mass spectrometer do?

Ions with different m/z values move at different speeds.

What happens at the detector?

Ions gain an electron, generating a current proportional to the abundance.

What does the mass spectrometer detect?

Generates a small current proportional to the abundance of the species.

What is the relative atomic mass (R.A.M)?

A weighted average of all isotopes present.

How is R.A.M calculated?

R.A.M = Σ(isotopic mass x % abundance) / 100.

What happens to the molecule in a mass spectrometer with electron impact ionisation?

It often breaks up and gives a series of peaks.

What does the largest peak in mass spectrometry represent?

The complete molecule or parent ion.

How does the peak differ in electron spray ionisation compared to electron impact?

There is no fragmentation.

Define first ionisation energy.

The enthalpy change when one mole of gaseous atoms forms one mole of gaseous ions with a single positive charge.

What are the three main factors that affect ionisation energy?

Nuclear attraction, distance from the nucleus, and shielding.

Why is there a big jump between successive ionisation energies?

Electrons are being removed from an inner shell leading to stronger attraction.

What is periodicity?

A repeating pattern across a period based on ionisation energy.

Why does helium have the largest first ionisation energy?

It has the closest electron shell to the nucleus without shielding effects.

What is the effect of increasing atomic number across a period on ionisation energy?

Generally, ionisation energy increases due to greater nuclear attraction.

What leads to a small drop in ionisation energy from Mg to Al?

Filling of the higher energy 3p sub shell in Al.

How does electron pairing in orbitals affect ionisation energy?

Repulsion between paired electrons makes it easier to remove one.

What happens to ionisation energy as you go down a group in the periodic table?

Ionisation energy decreases due to increased distance and shielding.

Define shielding in the context of ionisation energy.

Effect of inner shell electrons repelling outer shell electrons.

What type of ionisation energy is usually larger, first or second?

Second ionisation energy is generally larger.

What is the significance of measuring isotopes with mass spectrometry?

It helps in determining elemental composition on planets.

What technique is used to analyze larger organic molecules without causing fragmentation?

Electrospray ionisation.

What’s the importance of the mass spectrometer's vacuum environment?

To prevent air particles from interfering with ionisation.

Why do elements in the same group have similar ionisation energy trends?

They have similar distances and shielding effects from the nucleus.

How does ionization energy vary with the nuclear charge of an element?

Higher nuclear charge leads to stronger attractive forces, increasing ionisation energy.

Describe the impact of atomic size on ionisation energy.

Larger atoms have weaker attraction and lower ionisation energy.

What characteristic do isotopes share that affects their chemical properties?

The same electronic structure.

What effect does electron-electron repulsion have on ionisation energy?

It lowers ionisation energy for paired electrons in orbitals.

What role does the negative plate serve in mass spectrometry?

Attracts and draws positive ions from the detector.

Differentiate between fragmentation ions and molecular ions in mass spectrometry.

Fragmentation ions arise from broken molecules, whereas molecular ions represent intact molecules.

What pattern is observed when moving from left to right across a period?

Increasing ionisation energy due to rising nuclear charge.