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Atoms, Molecule, and Stoichiometry - Coggle Diagram
Atoms, Molecule, and Stoichiometry
Masses of atoms and molecule
there are
Unified atomic mass unit (u)
there are 3 parts contained
Definition: 1/12 mass of a Carbon-12
Symbol: u or Da
Value: 1,66 x 10^-27 kg
Relative atomic mass (Ar)
there are 3 parts
Ratio of average mass of atoms 1 u
Determined by weighted average of isotopes
Has no units (is a ratio)
Relative isotopic mass
have
Mass of a particular isotope (e.g., Carbon-13 is exactly 13)
Avogadro number of atoms (6.02 × 10²³)
Masses of compound
have
Relative molecular mass (Mr)
are
Sum of Ar of all atoms in one molecule
Applies to molecular compounds
No units
Relative formula mass (Mr)
are
Used for compounds containing ions (ionic compound)
Calculated the same way as Mr
Accurate relative atomic masses
there are
Mass spectrometry
there are 3 parts
Measures mass of each isotope
Compares relative abundance (isotopic abundance)
Results shown as mass/charge (m/e) ratio spectrum
Determination of Ar from mass spectra
the method:
(Isotopic mass x % abundance) / 100
Identification of organic compounds
there are
Molecular ion peak (M+)
have
Highest mass to charge ratio peak
Gives relative molecular mass
Fragmentation patterns
have
Caused by breaking covalent bonds
Common fragments (e.g., + CH3 at m/e 15, CH3CO + at m/e 43)
[M + 1] Peak
have
Caused by presence of 13C isotope (1.10% abundance)
Used to deduce number of carbon atoms (n)
[M + 2] and [M + 3] Peaks
there are
Detects presence of halogens (Cl, Br)
Cl ratio (M: [M + 2]) approx 3:1
Br ratio (M: [M + 2]) approx 1:1
Amount of substance and mole concept
there are
Mole definition
have 3 discussion
Amount of substance containing Avogadro constant of particles
Avogadro Constant (L or Nₐ): 6.02 × 10²³
Particles: atoms, molecules, ions, electrons
Molar mass (M)
have
Mass in grams of 1 mole of a compound
Units: g mol⁻¹
Moles and calculations
the formula
Moles = Mass (g) / Molar Mass (g mol⁻¹)
Chemical formulae and equations
there are
Formulae Deduction
have
Ionic Compounds
are
Balance positive and negative charges to equal zero
Ionic charge related to Periodic Table position
Use oxidation numbers (Roman numerals for transition elements)
Recall common compound ions (NO₃⁻, SO₄²⁻, NH₄⁺, etc.)
Covalent compounds
is
Work out bonds needed for stable electronic configuration
Balancing Equations
are
Same number of each type of atom on both sides
Do not change formulae; use stoichiometric numbers in front
Steps: Write formulae, count atoms, balance one by one
State Symbols
there are
Solid
Iiquid
Gas
aqueous solution
Ionic Equations
are
Show only ions participating in reaction
Omit spectator ions (ions that don’t change state/charge)
Atoms and charges must be balanced
Empirical and molecular formulae
there are
Empirical Formula
are
Simplest whole number ratio of elements
Found by mass determination (e.g., combustion)
Molecular Formula
are
Actual number of atoms of each element
Always a multiple of empirical formula
Requires empirical formula and relative formula mass (Mᵣ)
Hydrated Compounds
are
Contain water of crystallisation
Example: CuSO₄·5H₂O (hydrated) vs. CuSO₄ (anhydrous)
Mᵣ of hydrated salt = Mᵣ (salt) + Mᵣ (water)
Stoichiometry and mole calculations
there are
Reacting Masses
are
Use molar masses and balanced equations (stoichiometry).
Limiting Reagent: Not in excess, determines maximum product.
Excess Reagent: In surplus quantity.
Percentage Yield
the formula
Percentage Yield = (Actual / Predicted Yield) x 100
Solutions and Concentration
are
Concentration (mol dm^-3) = Moles (mol) / Volume (dm^3).
Titration used to find unknown concentration.
Convert cm^3 to dm^3 (divide by 1000).
Gas volumes
are
Avogadro's Hypothesis: Equal volumes of gases have equal moles.
Molar Gas Volume (r.t.p.): 1 mole = 24.0 dm^3
Used to deduce stoichiometry via volume ratios.
Significant Figures
are
Answer must match the least number of sig figs in data.
Avoid rounding until the final calculation step.