AQA Atomic Structure Revision

Atomic Structure Overview

• The video provides a revision overview of AQA atomic structure, covering key points that align with the specification.
• Accompanying PowerPoints are available for purchase via a link in the video description, useful for printing or revision.

Atom Composition and Properties

• Atoms comprise protons and neutrons in the nucleus, with electrons orbiting in shells around the nucleus.
• Protons carry a positive charge, neutrons have no charge, and electrons have a negative charge.
• Relative masses: protons = 1, neutrons = 1, electrons = 1/2000.
• Atoms are neutral due to an equal number of protons and electrons.
• In element notation, the top number indicates mass number (protons + neutrons), while the bottom number is the atomic/proton number.

Ions and Isotopes

• Ions differ from atoms with an unequal number of protons and electrons.
• Negative ions (anions) gain electrons, achieving a full, stable electron shell (e.g., O2- gains two electrons).
• Positive ions (cations) lose electrons, forming stable ionic compounds (e.g., Na+ loses one electron).
• Isotopes are elements with the same number of protons but a differing number of neutrons.
• Isotopes react similarly chemically due to identical electron numbers, but possess slightly different masses.

History of Atomic Models

• 1803: John Dalton proposed atoms as simple spheres.
• JJ Thompson's plum pudding model depicted the atom as positive pudding with negative electrons embedded within.
• Ernest Rutherford discovered the nucleus which is small and positively charged, surrounded by mostly empty space containing a cloud of electrons, and proved this with the gold leaf experiment.
• 1913: Niels Bohr proposed fixed energy levels (shells) after identifying issues with Rutherford's model, electrons emit or absorb radiation when moving between shells.
• The modern atom model includes shells and subshells which can be explained by ionization trends.

Time of Flight Mass Spectrometer

• Involves vaporizing a sample, ionizing it (often via electrospray ionization), acceleration, ion drift, and, finally, detection.
• Electrospray ionization sprays samples through a high-voltage jet, causing electron loss and creating gaseous, positively charged samples.
• Ions accelerate through charged plates/electric fields; particles with lower mass-to-charge (m/z) ratios accelerate quicker.
• Ions undergo drift at a constant speed, with lighter particles reaching the detector first, the detector measures electrical current created by the particle impact.

Relative Mass Definitions

• Relative atomic mass: Average mass of an element's atom on a scale relative to carbon-12 (exactly 12).
• Relative molecular mass: Average mass of a molecule on a scale relative to carbon-12.
• Relative isotopic mass: Mass of an isotope's atom on a scale relative to carbon-12.

Mass Spectra Interpretation

• Mass spectra display mass-to-charge ratio (m/z) on the x-axis and abundance (percentage or relative) on the y-axis.
• For isotopes, peaks indicate different isotopes; the height reflects abundance.
• With +1 charge, m/z equals isotopic mass. Double charges halve the m/z ratio.
• Relative atomic mass calculation: (abundance of isotope A × m/z of A) + (abundance of B × m/z of B) + ... then divide by total abundance.

Molecular Mass Spectra

• Molecules fragment in mass spectrometers.
• The Molecular ion peak (M+ peak) represents the unfragmented ionized molecule in the mass spectrometer, the last significant peak and its location on the spectra indicates the molecule's mass.

Electronic Configuration

• Electrons occupy four subshells: s, p, d, and f.
• S holds 2 electrons (one spherical orbital).
• P holds 6 electrons (three figure-eight-shaped orbitals).
• D holds 10 electrons.
• F holds 14 electrons.
• The first electron shell only contains an s orbital, the second shell contains s and p orbitals, the third shell contains s, p, and d orbitals.
• Electronic configuration is symbolized as 1s², where 1 = shell number, s = subshell, and 2 = number of electrons in the subshell.
• A 26 proton containing Ion has the electronic configuration of 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s²
• Orbitals are filled singly first, then paired up to minimize repulsion.

Ions and Electronic Configuration

• For ions, electrons are removed from the highest energy level first.
• Calcium 2+ loses two electrons from the 4s orbital, leaving 3p6 as the outer electron configuration.
• Transition metals behave differently, an electron moves from 4s to 3d for stability in chromium and copper.

Transition Metals and Electronic Configuration

• Transition metals exhibit a unique electron configuration behavior, like chromium.
• While calculating electrical configuration for Fe3+, three electrons are lost: two from 4s and one from 3d, in that order.
• During transition metal ionization, electrons are lost from the 4s orbital before the 3d orbital.

Ionization Energy

• Ionization energy: energy needed to remove 1 mole of electrons from 1 mole of gaseous atoms.
• State symbols must be included when showing ionization.
• Ionization is always endothermic (positive value).

Factors Affecting Ionization Energy

• Shielding: More electron shells between the nucleus and outer electron decrease required energy.
• The nucleus holds electrons so as the size of the atom increases the attractive force weakens, so atomic size is directly proportional to energy required to remove outer electrons.
• Nuclear charge: More protons increase attraction between the nucleus and outer electron, which takes more energy to remove.

Successive Ionization Energy

• Successive ionization involves taking multiple electrons, one by one, from an atom.
• Removing electrons from increasingly positive ions requires more energy.
• Significant jumps in successive ionization energy indicate removing an electron from a shell closer to the nucleus.

Group 2 Ionization Trends

• As you go down Group 2, ionization energy decreases.
• Atomic radius increases, causing electrons to be farther from the nucleus (weaker attraction).
• Shielding increases, weakening attraction.
• This data supports the existance of shells.

Period Ionization Trends

• Generally, ionization energy increases across a period due to an increase in protons and shielding is similar.
• Exceptions: decreases at aluminum (evidence of subshells) and sulfur (evidence of electron repulsion).
• Aluminum's outer electron is in a higher energy subshell, thus easier to remove.
• Sulfur's decrease is from electron repulsion in a paired orbital, needing less energy for removal.