AS Chemistry Unit 1: Equations and Formulae

AS Chemistry Unit 1: Formulae, Equations and Amounts of Substance

• Ionic Names and Formulae: "ate" ions have the highest number of oxygens, "ite" ions have fewer. Diatomic elements of group 7 include Fluorine (F), Bromine (Br), Iodine (I), Oxygen (O), Nitrogen (N), Chlorine (Cl), and Hydrogen (H). Examples include Sulfate (SO₄^2-), Sulfite (SO₃^2-), Nitrate (NO₃^-), Nitrite (NO₂^-), and Phosphate (PO₄^3-).

Writing and Balancing Chemical Equations

• Ionic Equations: Begin with the overall equation. Separate aqueous ionic compounds into their constituent ions. Keep insoluble and covalent compounds as they are. Cross out spectator ions (ions that appear on both sides). Example: CuSO₄(aq) + Mg(s) → MgSO₄(aq) + Cu(s) becomes Cu²⁺(aq) + SO₄^2-(aq) + Mg(s) → Mg²⁺(aq) + SO₄^2-(aq) + Cu(s). After cancelling spectator ions, the net ionic equation is Cu²⁺(aq) + Mg(s) → Mg²⁺(aq) + Cu(s).

RAM, RMM, RFM and Molar Mass

• RAM: Relative atomic mass (used for elements).
• RMM: Relative molecular mass (used for molecular compounds).
• RFM: Relative formula mass (used for ionic compounds).
• Molar Mass (MM): Mass of one mole of a substance. Calculating RFM involves adding the RAMs of all atoms in the compound.

The Mole

• Avogadro's Constant: The number of atoms in 12.000 g of carbon-12. Approximately 6.02 x 10²³.
• Mole: The amount of substance containing Avogadro's constant number of atoms, molecules, or groups of ions.

Calculating Moles (Solids)

• Formula: moles = mass (g) / RFM
• Example: Calculate the moles in 2.71 g of carbon dioxide (CO₂): moles = 2.71 g / 44 g/mol = 0.0616 mol.

Calculating Moles (Solutions)

• Formula: moles = volume (cm³) x concentration (mol/dm³) / 1000
• Note: Volume is usually given in cm³; convert to dm³ by dividing by 1000.

Limiting Reactants and Excess Reactants

• Limiting Reactant: Reactant that limits product formation in a reaction (runs out first).
• Excess Reactant: Reactant that remains after the limiting reactant is consumed.
• Calculations: Use the balanced equation to find the limiting reactant. Convert the given masses to moles, then compare moles of reactants using the mole ratios to determine the limiting reactant.

Water of Crystallisation

• Water of Crystallisation: Water chemically bonded within a crystal structure.
• Anhydrous Salt: Salt that does not contain water of crystallisation.
• Calculations: Find the mass of the anhydrous salt and water lost, find moles of anhydrous salt and water, divide moles of anhydrous and water by the moles of anhydrous salt to get the ratio of anhydrous salt to water, which is degree of hydrate.

Atomic Structure

• Atoms: Composed of protons, neutrons, and electrons.
• Subatomic Particles: Relative mass and charge.

Atomic Number (Z)

• Number of protons in an atom.

Mass Number (A)

• Sum of protons and neutrons in an atom.

Relative Atomic Mass (RAM)

• Average mass of the isotopes of an element relative to 1/12th the mass of carbon-12.

Relative Isotopic Mass (RIM)

• Mass of an isotope relative to 1/12th the mass of carbon-12.

Relative Formula Mass (RFM)

• Average mass of a formula unit relative to one-twelfth of the mass of an atom of carbon-12.

Relative Molecular Mass (RMM)

• Average mass of a molecule relative to one-twelfth of the mass of an atom of carbon-12.

Mass Spectrometry

• Mass Spectrometry: Technique used to determine the mass of atoms or molecules by ionizing samples and determining their mass-to-charge ratios.
• Mass Spectrum: Plot of relative abundance versus mass-to-charge ratio, which can identify isotopes of elements or compounds.
• Molecular Ion Peak: Peak in the spectrum corresponding to the molecular ion, showing the RMM.
• Fragments: Products formed when a compound or element ionizes and breaks up into smaller fragments, revealing their structure.

Electronic Configuration

• Energy Levels ("n"): Electrons occupy different energy levels, starting with the lowest energy levels closest to the nucleus.
• **Subshells (s, p, d, f):**Energy levels subdivided into subshells which are collections of orbitals. s orbitals are spherical, p orbitals are dumbbell-shaped, d orbitals are more complex shapes.
• Orbitals: Regions within an atom where an electron is likely to be found
• Max electrons in subshells: s holds 2, p holds 6, d holds 10, and f holds 14
• Electronic configuration of atoms and ions: Shows the arrangement of electrons in energy levels and subshells. This shows the filling order; 1s 2s 2p 3s 3p 4s 3d 4p...

Ionisation Energy

• Ionisation Energy: Energy needed to remove an electron from a gaseous atom or ion.
• First Ionisation Energy: Energy to remove the first electron.
• Successive Ionisation Energies: Energy required to remove additional electrons.