Atomic structure-physical chemistry Flashcards
What was John Dalton’s model of the atom (1803)?
Atoms are solid, indivisible spheres.
Each element is made of identical atoms with unique properties.
What was J.J. Thomson’s contribution to atomic structure (1897)?
Discovered the electron using the cathode ray experiment.
Proposed the “plum pudding model”: a positively charged sphere with negative electrons embedded inside.
What did Rutherford’s gold foil experiment reveal (1911)?
Most alpha particles passed through → atoms are mostly empty space.
Some were deflected → positive charge is concentrated in a small nucleus.
Led to the nuclear model: a dense, positive nucleus with electrons orbiting around it.
How did Niels Bohr refine the atomic model (1913)?
Proposed that electrons orbit the nucleus in fixed energy levels (shells).
Electrons can move between shells by absorbing or emitting energy (quantized energy levels).
What does the modern atomic model describe?
Based on quantum mechanics: electrons exist in orbitals, not fixed paths.
The exact location of an electron cannot be determined, only its probability of being in a certain region.
What are the relative charge and relative mass of protons, neutrons, and electrons?
Particle Relative Charge Relative Mass
Proton +1 1
Neutron 0 1
Electron -1 1/1836
Describe the structure of an atom.
Atoms consist of a central nucleus containing protons (positive) and neutrons (neutral).
The nucleus is surrounded by electrons (negative), which orbit in energy levels (shells).
The nucleus is very small compared to the overall size of the atom, but it contains most of the atom’s mass.
What is the mass number (A) and atomic number (Z)?
Mass number (A): Total number of protons and neutrons in an atom.
Atomic number (Z): Number of protons in an atom (also determines the element).
How do you determine the number of fundamental particles in an atom?
Protons = Atomic number (Z)
Neutrons = Mass number (A) - Atomic number (Z)
Electrons (Neutral Atom) = Number of protons (Z)
Electrons (Ion) = Z ± Charge
What are isotopes?
Atoms of the same element with the same number of protons but different numbers of neutrons.
Have the same chemical properties but different physical properties (e.g., density, boiling points).
What happens during electron impact ionisation in mass spectrometry?
Used for small molecules and elements.
A high-energy electron beam is fired at the sample.
An electron is knocked off, forming a positive ion: X(g) + e- > X+(g) + 2e-
The molecular ion (M⁺) may fragment into smaller ions.
What happens during electrospray ionisation in mass spectrometry?
Used for larger molecules (e.g., proteins).
Sample is dissolved in a volatile solvent and passed through a fine needle at high voltage.
Protons (H⁺) attach to the sample, forming a positive ion:
X(g) + H+ > XH+(g)
This method prevents fragmentation, giving clearer mass spectra.
What happens during acceleration in TOF mass spectrometry?
An electric field is applied, accelerating all ions.
All ions gain the same kinetic energy
Lighter ions move faster, while heavier ions move slower.
What happens during ion drift in TOF mass spectrometry?
Ions travel through a vacuum in a flight tube.
Since all ions have the same kinetic energy, their speed depends on their mass.
Lighter ions reach the detector first, while heavier ions take longer.
What happens during ion detection in TOF mass spectrometry?
Ions hit the detector and gain electrons, producing an electric current.
The size of the current is proportional to the number of ions hitting the detector.
The time taken to reach the detector is used to calculate the mass-to-charge ratio (m/z).
How is data from a mass spectrometer analyzed?
A mass spectrum is produced, showing peaks corresponding to different isotopes or molecular ions.
The x-axis (m/z ratio) shows mass-to-charge ratio.
The y-axis shows relative abundance.
The molecular ion peak (M⁺) represents the molecular mass of the compound.
How does mass spectrometry provide information about isotopes?
Measures relative isotopic mass and abundance of each isotope.
Can be used to calculate the relative atomic mass (Ar) of an element.
How is mass spectrometry used in chemistry?
Identifying elements – Each element has a unique mass spectrum.
Determining relative molecular mass (Mr) – Peak at the highest m/z value represents the molecular ion.
How do you calculate relative atomic mass (Ar) from isotopic abundance?
Ar = Σ(Isotopic mass x Relative abundance)/
Σ Relative abundance
How are electrons arranged in atoms?
Electrons occupy energy levels (shells), numbered n = 1, 2, 3, 4…
Each shell contains sub-shells (orbitals):
s (holds 2 electrons)
p (holds 6 electrons)
d (holds 10 electrons)
Electrons fill orbitals in order of increasing energy (Aufbau Principle).
What is the order of filling for electron sub-shells up to Z = 36?
1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p
Example: Calcium (Z = 20) → 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²
Transition Metals (Z = 21–36): 3d sub-shell fills after 4s
Example: Scandium (Z = 21): [Ar] 4s² 3d¹
How do electron configurations change for ions?
Metals (Cations) → Lose electrons from the highest energy level first
Example: Na⁺ (Z = 11) → [Ne] (loses 3s¹ electron)
Non-Metals (Anions) → Gain electrons to complete outer shell
Example: Cl⁻ (Z = 17) → [Ar] (gains 1 electron in 3p)
Transition Metals → Lose 4s electrons before 3d
Example: Fe²⁺ = [Ar] 3d⁶ (loses two 4s electrons first)
What is the first ionisation energy?
Energy required to remove one mole of electrons from one mole of gaseous atoms.
𝑋(𝑔)→𝑋+(𝑔)+𝑒−X(g)→X +(g)+e −
Measured in kJ mol⁻¹.
How do you write equations for successive ionisation energies?
First Ionisation Energy:
𝑋(𝑔)→X+(g) + e-
Second Ionisation Energy:
𝑋+(𝑔)→X2+(𝑔)+𝑒-
Third Ionisation Energy:
𝑋2+(𝑔)→𝑋3+(𝑔)+𝑒−
How does first ionisation energy change across Period 3?
General Increase across the period (Na → Ar):
Nuclear charge increases (more protons).
Same shielding (electrons added to same shell).
Stronger attraction between nucleus and outer electron → more energy needed to remove electron.
Exceptions:
Al < Mg → 3p electron in Al is higher in energy than 3s in Mg → easier to remove.
S < P → Sulfur has paired electrons in 3p (electron repulsion makes it easier to remove).
How does first ionisation energy change down Group 2?
Decreases down the group (Be → Ba):
More electron shells → increased shielding.
Outer electron is further from nucleus → weaker attraction.
Easier to remove electron → Lower ionisation energy.
How do ionisation energies provide evidence for electron shells and sub-shells?
Large jumps in ionisation energy → electron removed from a new shell (closer to nucleus).
Example: Mg (Z = 12)
1st & 2nd Ionisation Energy → electrons from 3s.
3rd Ionisation Energy (Huge jump!) → electron from 2p (inner shell).
Smaller drops in ionisation energy → Evidence for sub-shells (e.g., drop from Mg to Al).
