Chemistry essentials: 50 core concepts

All 50 cards

1. 1
   What is a mole?
   The amount of substance that contains $6.022 \times 10^{23}$ particles

   Since 2019 the mole is defined by fixing the Avogadro constant exactly.
2. 2
   Avogadro constant
   $N_A = 6.022 \times 10^{23}\,\mathrm{mol^{-1}}$
3. 3
   Ideal gas law
   $PV = nRT$

   P pressure, V volume, n amount in moles, R gas constant, T absolute temperature.
4. 4
   Value of the gas constant R
   $R \approx 8.314\ \mathrm{J\,mol^{-1}\,K^{-1}}$
5. 5
   Definition of pH
   $\mathrm{pH} = -\log_{10}[\mathrm{H^+}]$
6. 6
   pH of pure water at 25 °C
   7 (neutral)
7. 7
   Brønsted–Lowry acid
   A proton ($\mathrm{H^+}$) donor
8. 8
   Brønsted–Lowry base
   A proton acceptor
9. 9
   Lewis acid
   An electron-pair acceptor

   A Lewis base is an electron-pair donor.
10. 10
    Oxidation (OIL RIG)
    Loss of electrons

    Oxidation Is Loss, Reduction Is Gain.
11. 11
    Reduction (OIL RIG)
    Gain of electrons
12. 12
    Ionic bond
    Electrostatic attraction between oppositely charged ions, formed by electron transfer

    Example: $\mathrm{NaCl}$.
13. 13
    Covalent bond
    A pair of electrons shared between two atoms
14. 14
    Metallic bond
    Metal cations held together by a “sea” of delocalized electrons
15. 15
    Hydrogen bond
    An attraction between H bonded to N, O or F and a lone pair on another N, O or F
16. 16
    Electronegativity
    How strongly an atom attracts the electrons in a bond

    Fluorine is the most electronegative element.
17. 17
    Isotopes
    Atoms of the same element with different numbers of neutrons
18. 18
    Atomic number
    The number of protons in the nucleus
19. 19
    Mass number
    Protons + neutrons in the nucleus
20. 20
    Le Chatelier’s principle
    A system at equilibrium shifts to counteract a change in concentration, pressure or temperature
21. 21
    Catalyst
    Speeds up a reaction by lowering its activation energy, without being consumed
22. 22
    Exothermic reaction
    Releases heat to the surroundings; $\Delta H < 0$
23. 23
    Endothermic reaction
    Absorbs heat from the surroundings; $\Delta H > 0$
24. 24
    Gibbs free energy
    $\Delta G = \Delta H - T\Delta S$

    A reaction is spontaneous when $\Delta G < 0$.
25. 25
    Molarity
    Moles of solute per litre of solution: $c = \dfrac{n}{V}$
26. 26
    Moles from mass
    $n = \dfrac{m}{M}$

    m mass in grams, M molar mass in g/mol.
27. 27
    Molar mass of water
    About $18.02\ \mathrm{g/mol}$

    $2 \times 1.008 + 16.00$
28. 28
    Chemical formula of table salt
    $\mathrm{NaCl}$ (sodium chloride)
29. 29
    Noble gases
    Group 18: full valence shells, so they are very unreactive

    He, Ne, Ar, Kr, Xe, Rn.
30. 30
    Alkali metals
    Group 1 (Li, Na, K, …): soft metals that react vigorously with water
31. 31
    Halogens
    Group 17: F, Cl, Br, I, At
32. 32
    Valence electrons
    Electrons in the outermost shell, the ones that take part in bonding
33. 33
    Octet rule
    Atoms tend to gain, lose or share electrons to reach eight valence electrons
34. 34
    Functional group of alcohols
    Hydroxyl, $\mathrm{-OH}$
35. 35
    Functional group of carboxylic acids
    Carboxyl, $\mathrm{-COOH}$
36. 36
    Ketone
    A carbonyl group ($\mathrm{C{=}O}$) bonded to two carbon groups

    Example: acetone.
37. 37
    Aldehyde
    A carbonyl group at the end of a chain: $\mathrm{-CHO}$
38. 38
    Amine
    Nitrogen bonded to carbon groups and/or hydrogen, e.g. $\mathrm{-NH_2}$
39. 39
    Ester
    $\mathrm{-COO-}$ linking two carbon groups; formed from a carboxylic acid and an alcohol
40. 40
    General formula of alkanes
    $\mathrm{C_nH_{2n+2}}$
41. 41
    General formula of alkenes
    $\mathrm{C_nH_{2n}}$

    Alkenes contain a C=C double bond.
42. 42
    Structural isomers
    Compounds with the same molecular formula but different structures
43. 43
    Complete combustion of methane
    $\mathrm{CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O}$
44. 44
    Neutralization
    Acid + base → salt + water
45. 45
    Three common strong acids
    $\mathrm{HCl}$, $\mathrm{H_2SO_4}$, $\mathrm{HNO_3}$

    Strong acids dissociate fully in water.
46. 46
    Buffer solution
    A solution that resists changes in pH, usually a weak acid and its conjugate base
47. 47
    Half-life
    The time it takes for half of a reactant, or of radioactive nuclei, to be used up or decay
48. 48
    What does a titration measure?
    The concentration of a solution, by reacting it with a solution of known concentration
49. 49
    Standard temperature and pressure (IUPAC)
    $273.15\ \mathrm{K}$ (0 °C) and $100\ \mathrm{kPa}$ (1 bar)
50. 50
    Electron configuration of carbon
    $1s^2\,2s^2\,2p^2$