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Doc Brown's Chemistry  Advanced Level Inorganic Chemistry Periodic Table Revision Notes

Part 4. Revising Survey of Period 2 Li to Ne

4.3 Period 2 trends in bonding, formulae & reactions

The trends in the physical and chemical character of the elements is discussed first. The trends in bond type and formula of the compounds of the elements of Period 2 of the Periodic Table are tabulated and explained. The trends in valency and oxidation states of the elements in their compounds is also discussed and explanations provided on the basis of their electron configurations. The oxides, chlorides and hydrides of all of the Period 2 elements are tabulated with their formulae and type of bonding. The trends in the Period 2 elements chemical reaction with oxygen, water and chlorine are described and explanations provided with symbol equations, as are the reactions of the Period 2 oxides and chlorides with water and acids or alkalis. Finally, two series of isoelectronic species are tabulated in terms of their, nuclear charge, ion charge/neutral atom and atomic or ionic radii.

For non-A level students (c) doc b KS4 Science GCSE/IGCSE Periodic Table notes links

 INORGANIC Part 4 Period 2 survey sub-index : 4.1 Period 2 Survey of the individual elements : 3. lithium : 4. Beryllium : 5. Boron : 6. Carbon : 7. Nitrogen : 8. Oxygen : 9. Fluorine : 10. Neon * 4.2 Period 2 element trends and explanations of physical properties * 4.3 Period 2 element trends in bonding, structure, oxidation state, formulae & reactions

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


Survey of Period 2: Li across to Ne (8 elements, Z = 3 to 10)

4.3 Period 2 trends in bonding, structure, oxidation state, formulae and reactions

M+ X- ionic bond, Mδ+-Xδ+ polar bond and M-X a relatively non-polar bond (no partial charges shown)

Element Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
old/latest Group 1 2 3/13 4/14 5/15 6/16 7/17 0/18
ZSymbol 3Li 4Be 5B 6C 7N 8O 9F 10Ne
Structure of element solid metallic lattice of Li+ and free e- solid metallic lattice of Be2+ and free e- solid giant covalent lattice Bn solid giant covalent lattice Cn small gaseous covalent diatomic molecule N2 small gaseous covalent diatomic molecule O2 small gaseous covalent diatomic molecule F2 gaseous single atoms
Electron configuration 1s22s1 1s22s2 1s22s22p1 1s22s22p2 1s22s22p3 1s22s22p4 1s22s22p5 1s22s22p6
common oxidation states in compounds e.g. in oxides, chlorides, hydrides +1

max +1

+2

max +2

+3

max +3

+4, (+2 in CO, -4 to +4 in organic compounds)

max +4

-1 to +5 (max), -3, +3 & +5 most common

max +5

-2, -1, +2 in F2O

max +2

-1 -
Electronegativity of element 0.98 1.57 2.04 2.55 3.04 3.44 3.98 4.84
Formula of oxides Li2O BeO B2O3 CO2 (CO) N2O, NO, N2O3, NO2, N2O5 O2, O3 F2O -
Bonding and structure of oxides ionic lattice ionic lattice with covalent character giant covalent lattice gaseous small covalent molecules gaseous small covalent molecules gaseous small covalent molecules gaseous small covalent molecule -
electronegativity difference X-O (O is 3.44) nature of bond 2.46

Li+ O2-

1.87

Beδ+-Oδ-

1.40

Bδ+-Oδ-

0.89

δ+C=Oδ-

0.44

Nδ+-Oδ-

0.00

O-O

0.54

Oδ+-Fδ-

-
Formula of chlorides LiCl BeCl2 BCl3 CCl4 NCl3 Cl2O or OCl2 ClF or FCl -
bonding and structure of chlorides ionic lattice layered covalent lattice small covalent gaseous molecule small covalent liquid molecule small covalent liquid molecule non-polar small covalent gaseous molecule small covalent gaseous molecule -
electronegativity difference X-Cl (Cl is 3.16) nature of bond 2.18

Li+ Cl-

1.29

Beδ+-Clδ-

1.12

Bδ+-Clδ-

0.61

Cδ+-Clδ-

0.12

N-Cl

0.00

Cl-Cl

0.82

Clδ+-Fδ-

-
Formula of hydride LiH BeH2 BH3?, B2H6 etc. CH4 NH3 H2O or OH2 HF or FH -
bonding and structure of hydride ionic lattice layered covalent polymer lattice small covalent gaseous molecule small covalent gaseous molecule polar small covalent gaseous molecule polar small covalent liquid molecule polar small covalent gaseous molecule -
electronegativity difference X-H (H is 2.20) nature of bond 1.22

Li+ H-

0.63

Beδ+-Hδ-

0.16

B-H

0.35

C-H

1.02

Nδ--Hδ+

1.24

Oδ--Hδ+

1.78

Hδ+-Fδ-

-
  • Advanced Inorganic Chemistry Page Index and LinksThe structure and physical properties of the elements:

    • The trend is metal lattice ==> giant covalent structure ==> small covalent molecules.

    • Lithium and beryllium are silvery solids, with a metal lattice structure, and are good conductors of heat/electricity due to the delocalised free electrons moving between the immobile metal ions.

      • The melting/boiling points increase from Li ==> Be due to double the potential number of delocalised bond electrons that may contribute to bonding.

    • Boron Bn and carbon Cn have a non-metallic giant covalent structure (where n is a very large number indeed) and are poor conductors of heat/electricity (though Cn(graphite) shows some metallic character as a 'moderate' conductor). The strong 3D bonding gives boron and carbon (diamond) very high melting/boiling points and great hardness.

      • Actually, the diamond/graphite allotropes of carbon sublime at temperatures over 3500oC. Graphite with its huge 2D planes of atoms also has a very high melting/boiling point, though it is physically weak because the 2D layers of carbon atoms are only held by weak intermolecular forces and slip over each other under stress

    • Nitrogen N2, oxygen O2 and fluorine F2 have a simple-small covalent molecule structure and neon consists of single atoms. The molecules are only held together by the weakest of the intermolecular forces, namely the instantaneous dipole - induced dipole forces, and consequently have very low melting/boiling points.

      • From left to right the elements become less metallic and more non-metallic.

    • -

  • Advanced Inorganic Chemistry Page Index and LinksElectron configuration and oxidation states

    • Electron configurations of  2,1 or 1s22s1 to 2,8 or 1s22s22p6  

      • Filling the s orbital (max 2 e-'s) gives the metallic s-block elements of Groups 1-2,

      • filling the p orbitals gives the predominantly non-metallic p block elements of Groups 3-7 & 0 (13-18) for Period 2.

    • Oxidation states in compounds (numerically = valency) are: Li (+1 only), Be (+2 only), B (+3 only), C (usually +4*), N (-3, +1 to +5), O (usually -2, but can be -1 and +2), F (-1 only), Ne has no stable compounds due to the full outer quantum level (shell) being full, conferring extra electronic stability on the atom.

      • From Li to N the maximum oxidation state is equal to the 'old' group number and the 'highest' oxide formulae can be predicted up to N and the chloride formula up to C (period 2 elements cannot exceed a co-ordination number of 4 due to valance orbital restrictions, in periods 3-4 the maximum is raised to 6.

        • So in the 'highest' oxides you can go from +1 to +5 for Groups 1 to 5, then drops to +2 for fluorine

        • Li2O, BeO, B2O3, CO2, N2O5 using all available 1-5 outer 2s and 2p valence electrons, lastly F2O

        • and the chloride formula is derived from oxidation state +1 to +4 for Groups 1 to 4/14 (1-4 outer valency electrons), then declines +3, +2, -1

        • LiCl, BeCl2, BCl3, CCl4 then NCl3, Cl2O (OCl2), ClF (FCl)

      • * C can be (+2) in CO and from -1 to + 4 in organic compounds - a complex area in terms of oxidation state - but this knowledge is not needed for UK ASA2 level, if interested see Redox Reactions Part 3.

    • -

  • Advanced Inorganic Chemistry Page Index and LinksReaction of element with oxygen and the structure of the oxide

(Gp 1) 4Li(s) + O2(g) ==> 2Li2O(s) slow, fast when heated (Gp 2) 2Be(s) + O2(g) ==> 2BeO(s) at high temperature
(Gp 3) 4B(s) + 3O2(g) ==> 2B2O3(s) at high temperature (Gp 4) C(s) + O2(g) ==> CO2(g) at high temperature
(Gp 5) N2(g) + O2(g) ==> 2NO(g) at high temperature, NO rapidly forms NO2 in air/oxygen (Gp 6) in ozone layer O + O2 ==> O3
(Gp 7) Fluorine - no reaction (Gp 0) Neon - no reaction
  • Reaction with oxygen and the structure of the oxide

    • The metal Li burns in air/oxygen to form a giant ionic lattice oxide Li2O or (Li+)2O2-

    • Beryllium forms a giant lattice oxide (BeO has an intermediate ionic-covalent structure).

    • Boron forms a giant covalent lattice of B2O3.

    • Carbon forms simple covalent molecular CO2 gas (or CO).

    • Nitrogen forms a variety of simple molecular covalent gaseous oxides upto N2O5.

    • Fluorine can form F2O gas.

    • In terms of the maximum oxidation state the observed formulae comply with +1 to + 5 for Groups 1-5, for fluorine it is -1

    • Li2O, BeO, B2O3, CO2, N2O5, (O2), F2O

    • The overall bonding pattern, from left to right is giant ionic lattice => giant covalent lattice => small covalent molecules.

    • The change in bonding character from ionic to covalent in the oxide, follows the decreasing difference in electronegativity between that of the period 2 element and oxygen.

    • -

  • Advanced Inorganic Chemistry Page Index and LinksReaction of the oxides with water, acids and alkalis

(Gp 1) Li2O(s) + H2O(l) ==> 2LiOH(aq)  pH 13-14 strong base (Gp 2) BeO no reaction, but amphoteric in nature
(Gp 3) B2O3 no reaction, but weakly acidic (Gp 4) CO2(aq) + 2H2O(l) <=> H3O+(aq) + HCO3-(aq)  ~pH 5 weak acid
(Gp 5) N2O5(s) + H2O(l) ==> 2HNO3(aq)  pH 1 strong acid (Gp 6) oxygen has no reaction with water
(Gp 7) Cl2O(g) + H2O(l) ==> 2HClO(aq) weak acid  pH ~3 weak acid

Cl2O7(g) + H2O(l) ==> 2HClO4(aq)  pH1 strong acid

(Gp 0) argon - no oxide
  • The chemical character of the oxides - reaction with water, acids and alkalis

    • Lithium oxide Li2O is basic and forming the alkali lithium hydroxide in water and this gives salts with acids.

      • Li2O(s) + H2O(l) ==> 2LiOH(aq)

      • LiOH(aq) + HCl(aq) ==> LiCl(aq) + H2O(l)

    • Beryllium oxide BeO has no reaction but is amphoteric and forms salts with acids and alkalis.

      • BeO(s) + 2HCl(aq) ==> BeCl2(aq) + H2O(l)

      • BeO(s) + 2NaOH(aq) + H2O(l) ==> Na2[Be(OH)4](aq) 

    • Boron oxide B2O3 is weakly acidic and reacts with strong alkalis to form borate salts.

    • Carbon dioxide CO2 is weakly acidic forming salts with alkalis e.g.

      • CO2(aq) + NaOH(aq) ==> NaHCO3(aq) + H2O(l)

    • Nitrogen(I) oxide N2O (dinitrogen oxide) and nitrogen(II) oxide NO (nitrogen monoxide) are neutral oxides,

      • but nitrogen(III) oxide N2O3, nitrogen(IV) oxide NO2 (nitrogen dioxide) and nitrogen(V) oxide N2O5 are moderately to strongly acidic oxides.

      • Generally speaking, in a series of oxides of the same element, the higher the oxidation state of X in a 'XxOy' series, the more acidic is the oxide.

        • Nitrogen(V) oxide reacts with water to form nitric(V) acid,

        • N2O5(l) + H2O(l) ==> 2HNO3(aq)

        • and nitric(V) acid is neutralised by alkali to form salts e.g.

        • 2HNO3(aq) + NaOH(aq) ==> 2NaNO3(aq) + H2O(l)

    • Oxygen(II) fluoride (oxygen difluoride) F2O is also acidic in principal but I don't know if it reacts with water?

    • So, the general patterns across the period from left to right are

    • ionic lattice bonding ==> giant covalent structure ==> small covalent molecules

      • The change in bonding character from ionic to covalent in the oxide follows the decreasing difference in electronegativity between that of the element and oxygen.

    • In terms of chemical character ...

    • basic oxide => amphoteric oxide => weakly acidic oxide => strongly acidic oxide

    • and metal basic oxides ==> metal amphoteric oxides ==> non-metal oxides

    • This is chemically characteristic of metallic compound ==> non-metallic compound character.

    • -

  • Advanced Inorganic Chemistry Page Index and LinksReaction of element with chlorine and the structure of the chloride

(Gp 1) 2Li(s) + Cl2(g) ==> 2LiCl(s) (Gp 2) Be(s) + Cl2(g) ==> BeCl2(s) 
(Gp 3) 2B(s) + 3Cl2(g) ==> 2BCl3(l) needs high temperature (Gp 4) carbon has no reaction with chlorine
(Gp 5) nitrogen has no reaction with chlorine (Gp 6) oxygen has no reaction with chlorine
(Gp 7) Cl2(g) + F2(g) ==> 2ClF(g) (Gp 0) neon has no reaction with chlorine
  • Reaction with chlorine and the structure of the chloride

    • The first three element will combine directly on heating in chlorine to give the expected chloride formula.

    • Lithium gives a giant ionic lattice of LiCl or Li+Cl-,

    • Beryllium a polymeric covalent lattice of BeCl2.

    • Boron forms small covalent molecules of BCl3.

    • The others are also small covalent molecules, made indirectly, CCl4, NCl3, Cl2O

    • In terms of the chloride the (oxidation states) in the chlorides are

    • (+1) LiCl, (+2) BeCl2, (+3) BCl3, (+4) CCl4, (+3) NCl3, (-2) Cl2O, (+1) ClF, no neon chloride

    • So the number of atoms of chlorine combined with the Period 2 element (the valency) follows the pattern

      • 1  2  3  4  3  2  1  0

    • The overall pattern, from left to right across period 2 is ...

    • giant ionic lattice => polymeric covalent lattice ==> small covalent molecules.

    • The change in bonding character from ionic to covalent in the chloride, follows the decreasing difference in electronegativity between that of the element and chlorine, as in the case of oxides.

    • This is chemically characteristic of metallic ==> non-metallic element character.

    • -

  • Advanced Inorganic Chemistry Page Index and LinksReaction of the chlorides with water

(Gp 1) LiCl(s) + aq ==> Li+(aq) + Cl-(aq)  just dissolves, neutral ~pH 7 (Gp 2) BeCl2(s) + 2H2O(l) <=> Be(OH)2(s) + 2HCl(aq)  hydrolysis giving an acid solution  
(Gp 3) BCl3(l) + 3H2O(l) ==> B(OH)3(aq)* + 3HCl(aq)  hydrolysis giving an acid solution (Gp 4) CCl4 no reaction with water
(Gp 5) NCl3(l) + 2H2O(l) ==> HNO2(aq) + 3HCl(aq)  hydrolysis giving an acid solution (Gp 6) Cl2O(g) + H2O(l) ==> 2HClO(aq)  hydrolysis giving an acid solution
(Gp 7) ClF + H2O ==> acidic solution ??? (Gp 0) neon has no chloride
  • The reaction of chlorides with water

    • Ionic LiCl dissolves to form a nearly neutral solution of hydrated lithium and ions.

    • The covalent beryllium chloride BeCl2 hydrolyses to give beryllium hydroxide and hydrochloric acid.

    • Boron trichloride BCl3 similarly hydrolyse to form acid solutions.

    • Tetrachloromethane CCl4 (carbon tetrachloride) is quite stable in water.

    • Nitrogen trichloride NCl3 slowly hydrolyses to give an acid solution.

    • Chlorine(I) oxide Cl2O hydrolyses to give an acidic solution.

    • FCl or ClF gives acidic solution ???

    • The general trend is for ionic chloride salts to give nearly neutral solutions => covalent chlorides that hydrolyse to give acidic solutions.

    • -

  • Advanced Inorganic Chemistry Page Index and LinksReaction of element with water

(Gp 1) 2Li(s) + 2H2O(l) ==> 2LiOH(aq) + H2(g) (Gp 2) beryllium has no reaction with cold water
(Gp 3) boron has no reaction with water (Gp 4) C(s) + H2O(g) ==> CO(g) + H2(g) at high temperature
(Gp 5) nitrogen has no reaction with water (Gp 6) oxygen has no reaction with water
(Gp 7) 2F2(g) + 2H2O(l) ==> 4HF(aq) + O2(g) (Gp 0) argon has no reaction with water
  • The reaction of the element with water

    • The reactive metal Li gives the hydroxide and hydrogen.

    • Beryllium and boron have no reaction with water.

    • Carbon reacts at high temperature.

    • Nitrogen and oxygen have no reaction with water.

    • Fluorine reacts violently forming oxygen and hydrogen fluoride.

      • Fluorine is such a powerful oxidising agent that it can oxidise water itself!

    • The 'limited' pattern for period 2 (or any other period), is to have reactive metals on the left forming an alkaline solution of a hydroxide and hydrogen and non-metals on the right forming acid solutions IF they react with water (only fluorine).

    • -

  • Advanced Inorganic Chemistry Page Index and LinksThe hydrides MHx

    • For hydrides the difference in electronegativity works both ways!

    • From left to right across the period you change from an ionic lithium hydride crystal lattice e.g.

      • Li+H- to small non-polar molecule covalent hydrides (methane CH4)

      • and then a polar weakly basic covalent hydride molecule (ammonia NH3)

      • and finally a quite acidic polar covalent molecule (hydrogen fluoride HF).

    • The formulae follow a simple period pattern of rising and falling valency combinations.

      • LiH  BeH2  B2H6 (= to BH3)  CH4  NH3 H2O  HF no neon hydride

      • valency combing power of the element gives a 1  2  3  4  3  2  1  0 pattern

    • On reaction with water, the ionic metal hydrides at the start of the period give an alkaline solution

      • e.g. LiH(s) + H2O(l) ==> LiOH(aq) + H2(g)

        • MgH2(s) + 2H2O(l) ==> Mg(OH)2(aq/s) + 2H2(g)

    • In the middle are neutral hydrides like methane which in contact with water do not change the pH.

    • Then you get weak base ==> moderately strongly acidic hydrides when they dissolve in water e.g.

      • weak base: NH3(aq) + H2O(l) <=> NH4+(aq) + OH-(aq)

      • quite strong acid: HF(aq) + H2O(l) ==> H3O+(aq) + F-(aq)

    • So things are a bit complicated with hydrides on period 2 and not the greatest of patterns!

    • -

  • Radii of isoelectronic ions

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

  • The table below considers the isoelectronic anions associated with Periods 2 (and the table continues with Period 3 cations).

  • 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
  • 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 for the same number of electrons, 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.

  • More isoelectronic radii are at the end of the Period 3 survey pages or the end of the Period 4 survey pages.


Advanced Inorganic Chemistry Page Index and Links

WHAT NEXT?

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

 INORGANIC Part 4 Period 2 survey sub-index : 4.1 Period 2 Survey of the individual elements : 3. lithium : 4. Beryllium : 5. Boron : 6. Carbon : 7. Nitrogen : 8. Oxygen : 9. Fluorine : 10. Neon * 4.2 Period 2 element trends and explanations of physical properties * 4.3 Period 2 element trends in bonding, structure, oxidation state, formulae & reactions

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

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