IB Chemistry SL
Comprehensive flashcards for the IB Diploma Programme Chemistry Standard Level (current guide, first exams 2025). Covers the SL common core across the two organising concepts — Structure and Reactivity — plus tools and the nature of science.
Ämne: Kemi · Nivå: Gymnasium (16–19) · 440 kort
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- The mole (mol) is the SI unit for amount of substance. One mole contains exactly 6.02 × 10²³ specified entities (atoms, molecules, ions, etc.).
- The Avogadro constant (Nₐ or L) is 6.02 × 10²³ mol⁻¹. It is the number of entities in one mole of any substance.
- Molar mass (M) is the mass of one mole of a substance, in g mol⁻¹. It is numerically equal to the relative atomic or molecular mass.
- Amount of substance (n) is calculated from mass and molar mass: n = m / M, where m is mass in g and M is molar mass in g mol⁻¹.
- The number of entities (N) equals amount in moles times the Avogadro constant: N = n × Nₐ.
- Relative atomic mass (Aᵣ) is the weighted mean mass of an atom of an element relative to 1/12 the mass of a carbon-12 atom. It has no units.
- An empirical formula gives the simplest whole-number ratio of atoms of each element in a compound (e.g. CH₂O for glucose).
- A molecular formula gives the actual number of atoms of each element in a molecule. It is a whole-number multiple of the empirical formula (e.g. C₆H₁₂O₆ for glucose).
- Avogadro's law states that equal volumes of all gases, at the same temperature and pressure, contain the same number of molecules (particles).
- The molar volume of an ideal gas is 22.7 dm³ mol⁻¹ at STP (standard temperature and pressure: 0 °C / 273 K and 100 kPa).
- The ideal gas equation is PV = nRT, where P is pressure (Pa), V is volume (m³), n is amount (mol), R is the gas constant (8.31 J K⁻¹ mol⁻¹) and T is temperature (K).
- Temperature in gas calculations must always be in kelvin (K). Convert from Celsius using T(K) = θ(°C) + 273.
- Concentration (mol dm⁻³) is amount of solute divided by volume of solution: c = n / V, where V is in dm³. It is also called molarity.
- A standard solution is a solution of accurately known concentration, prepared by dissolving a known mass of solute and making up to a precise volume in a volumetric flask.
- Atoms contain a dense central nucleus of protons and neutrons, surrounded by electrons occupying regions of space (the electron cloud).
- Relative charges of subatomic particles: proton +1, electron −1, neutron 0. Relative masses: proton 1, neutron 1, electron ~1/1836 (negligible).
- The atomic number (Z) is the number of protons in an atom's nucleus. It defines the element and equals the number of electrons in a neutral atom.
- The mass number (A) is the total number of protons plus neutrons in an atom's nucleus. Number of neutrons = A − Z.
- Isotopes are atoms of the same element (same number of protons) with different numbers of neutrons, and therefore different mass numbers.
- Isotopes of an element have identical chemical properties (same electron configuration) but slightly different physical properties such as density and rate of diffusion.
- Relative atomic mass is calculated from isotopic abundances: Aᵣ = Σ(isotope mass × fractional abundance). For chlorine: (35 × 0.75) + (37 × 0.25) = 35.5.
- A mass spectrum plots relative abundance against mass/charge ratio (m/z). Each peak represents an isotope; peak heights give relative abundances used to calculate Aᵣ.
- A cation is a positively charged ion formed when an atom loses electrons. An anion is a negatively charged ion formed when an atom gains electrons.
- In the Bohr model, electrons occupy fixed energy levels (shells) around the nucleus. Electrons can only exist in these discrete levels, not in between.
- When an electron absorbs energy it is promoted to a higher energy level (excited state). When it falls back, it emits a photon of light of a specific frequency.
- Emission line spectra are discrete (discontinuous) lines, providing evidence that electrons occupy discrete energy levels. Lines converge at higher energy/frequency.
- In the hydrogen emission spectrum, the Lyman series (UV) results from transitions to n=1, the Balmer series (visible) from transitions to n=2, and the Paschen series (IR) from transitions to n=3.
- The main energy levels (shells) are divided into sublevels: s, p, d and f. An s sublevel holds up to 2 electrons, p up to 6, d up to 10, f up to 14.
- The maximum number of electrons in a main energy level n is 2n²: level 1 holds 2, level 2 holds 8, level 3 holds 18, level 4 holds 32.
- The Aufbau principle states that electrons fill the lowest-energy sublevels first. The 4s sublevel fills before 3d because it is at a slightly lower energy.
- The full electron configuration of sulfur (Z=16) is 1s² 2s² 2p⁶ 3s² 3p⁴. The condensed (noble gas) form is [Ne] 3s² 3p⁴.
- First ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous atoms: X(g) → X⁺(g) + e⁻.
- Successive ionisation energies of an element always increase, because each electron is removed from an increasingly positive ion. Large jumps reveal changes between main energy levels (shells).
- A graph of successive ionisation energies provides evidence for the number of electrons in each shell, supporting the model of discrete energy levels.
- The percentage yield = (actual yield / theoretical yield) × 100%. It is always 100% or less because of incomplete reactions and losses.
- The limiting reactant is the reactant that is completely consumed first; it determines the maximum amount of product. Other reactants are in excess.
- Atom economy = (molar mass of desired product / total molar mass of all products) × 100%. High atom economy means less waste and more sustainable reactions.
- Ionic bonding is the electrostatic attraction between oppositely charged ions, formed by the transfer of electrons from a metal to a non-metal.
- Ionic compounds form giant ionic lattices: a regular 3D arrangement of alternating cations and anions held by strong electrostatic forces in all directions.
- Ionic compounds have high melting points (strong lattice forces), are brittle, and conduct electricity only when molten or dissolved (ions become mobile).
- A covalent bond is a shared pair of electrons between two atoms, resulting from the electrostatic attraction between the shared electrons and the two nuclei.
- A single bond shares one electron pair, a double bond two pairs, and a triple bond three pairs. Bond strength increases and bond length decreases from single to triple.
- A coordinate (dative) covalent bond is a covalent bond in which both shared electrons come from the same atom, e.g. the bond to H⁺ in the ammonium ion NH₄⁺.
- VSEPR theory: electron domains (bonding pairs and lone pairs) around a central atom repel and arrange themselves as far apart as possible, determining molecular shape.
- Two electron domains give a linear shape with 180° bond angle (e.g. CO₂, BeCl₂).
- Three bonding domains give trigonal planar (120°, e.g. BF₃). Three domains with one lone pair give bent/V-shaped (e.g. SO₂, ~118°).
- Four bonding domains give tetrahedral shape with 109.5° bond angles (e.g. CH₄).
- Four domains with one lone pair give trigonal pyramidal (~107°, e.g. NH₃). Four domains with two lone pairs give bent (~104.5°, e.g. H₂O).
- Lone pairs repel more strongly than bonding pairs, so each lone pair reduces the bond angle by about 2.5° compared with the ideal angle.
- Electronegativity is the relative ability of an atom to attract a shared pair of electrons in a covalent bond. Fluorine is the most electronegative element.