Doc Brown's Chemistry  Periodic Table Revision Notes

Part 6. Survey of Period 4 & important trends down a group: 6.3 Period 4 trends in bonding, formulae and oxidation state

Revision notes for GCE Advanced Subsidiary Level AS Advanced Level A2 IB Revise AQA GCE Chemistry OCR GCE Chemistry Edexcel GCE Chemistry Salters Chemistry CIE Chemistry revising courses for pre-university students (equal to US grade 11 and grade 12 and Honours/honors level courses) GCSE Periodic Table notes

INORGANIC Part 6 Period 4 survey & group trends page sub-index: 6.1 Survey of Period 4 elements * 6.2 Period 4 element trends in physical properties * 6.3 Period 4 element trends in bonding,  formulae and oxidation state * 6.4 Important element trends down a Group

Advanced Level Inorganic Chemistry Periodic Table Index * Part 1 Periodic Table history * Part 2 Electron configurations, spectroscopy, hydrogen spectrum, ionisation energies * Part 3 Period 1 survey H to He * Part 4 Period 2 survey Li to Ne * Part 5 Period 3 survey Na to Ar * Part 6 Period 4 survey K to Kr and important trends down a group * Part 7 s-block Groups 1/2 Alkali Metals/Alkaline Earth Metals * Part 8  p-block Groups 3/13 to 0/18 * Part 9 Group 7/17 The Halogens * Part 10 3d block elements & Transition Metal Series * Part 11 Group & Series data & periodicity plots * All 11 Parts have their own sub-indexes near the top of the pages

6.3 Period 4 trends in bonding and  formulae

Krypton is omitted since there is no relevant or comparable chemistry and the table is more likely to fit on the page!

Abbreviations: ampho = amphoteric, cov = covalent

• The patterns across Period 4 are not as clear cut as for periods 2 and 3 - one reason being the interjection of the 3d block of metals

• Metallic or non-metallic character:

  • From far left (metallic) to the far right (non-metallic) the non-metallic character increases as the electronegativity and ionisation energies increase.

  • This trend shows up as the electronegativity difference in M-X decreases (M to the left of X)

    • (i) the ionic bonding of the giant ionic lattice ==> covalent bonding character of small molecules of the oxides and chlorides

    • (ii) the oxide changes from basic ==> amphoteric ==> acidic

    • BUT within the 3d block the patterns are quite complicated and the oxidation state of the metal very much determines the structural and chemical character of the compound.

• Oxidation states

  • From potassium (+1) to manganese (+7) the maximum oxidation state is determined by the maximum number of outer valency electrons.

  • After Mn, there is a tendency to fall to a stable +2 state e.g. cobalt, nickel, copper and zinc.

  • Beyond zinc, the last element in the 3d block, the maximum oxidation state is governed by the maximum number of s + p electrons beyond the full 3d sub-shell i.e. from gallium to bromine the maximum oxidation state rises from +3 to +7.

• Oxides - formulae, bonding and chemical character

  • Ionic lattice  ==> covalent character of the oxides and chlorides

  • and in chemical character the oxide changes from basic ==> amphoteric ==> acidic.

  • The oxide of maximum oxidation state for potassium to manganese is determined by the maximum number of outer valency electrons (from 1 to 5).

  • Again the patterns within the 3d block are complicated.

• Chlorides - formulae, bonding and chemical character

  • the ionic ==> covalent character of the oxides and chlorides as the electronegativity difference in M-X decreases (M to the left of X)

• Radii of isoelectronic ions

• Isoelectronic means species having the same total number of electrons.

• The table below considers the isoelectronic ions associated with Periods 2, 3 and 4.

• isoelectronic system	Group 4/14	Group 5/15	Group 6/16	Group 7/17	(Group 0/18)	Group 1	Group 2	Group 3/13
  Period	Period 2					Period 3
  [Ne] 10e 1s22s22p6	C4-	N3-	O2-	F-	(Ne)	Na+	Mg2+	Al3+
  total nuclear charge	+6	+7	+8	+9	(+10)	+11	+12	+13
  radius in picometre (pm)	260	171	140	136	(38-112*)	95	65	50
  name of ion	carbide	nitride	oxide	fluoride	(neon)	sodium	magnesium	aluminium
  Period	Period 3					Period 4
  [Ar] 18e 1s22s22p63s23p6	Si4-	P3-	S2-	Cl-	(Ar)	K+	Ca2+	Sc3+
  nuclear charge	+14	+15	+16	+17	(+18)	+19	+20	+21
  radius  in picometre (pm)	271	212	184	181	(71-154*)	133	99	81
  name of ion	silicide	phosphide	sulfide	chloride	(argon)	potassium	calcium	scandium

• Excluding the noble gases themselves, there is a clear pattern of decreasing ionic radius with increase in nuclear charge (+ atomic/proton number) for the two isoelectronic series tabulated above.

• From left to right the proton/electron ratio is steadily increasing so that the electrons are experiencing an increasingly greater attractive force of the nucleus, hence the steady decrease in radii for an isoelectronic series.

• * all sorts of values are quoted for noble gas radii e.g. atomic, covalent and ionic, but most don't fit in the pattern above which is quite clear for all the cations and anions listed.

See also 4.1 Period 2 Survey of the individual elements, 4.2 Period 2 element trends and explanations of physical properties * 4.3 Period 2 element trends in bonding, structure, oxidation state, formulae & reactions, 5.1 Period 3 survey of elements, 5.2 Period 3 element trends & explanations of physical properties, 5.3 Period 3 element trends in bonding, structure, oxidation state, formulae & reactions, 6.2 Period 4 element trends in physical properties, 6.4 Important element trends down a Group

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