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Trends in atomic size (radius)

Trends in atomic size (radius). Definition of atomic radius: Covalent radius:. The covalent bond length in H 2 molecule is the distance between the two nuclei.

jacqueline-clay
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Trends in atomic size (radius)

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  1. Trends in atomic size (radius) • Definition of atomic radius: Covalent radius: • The covalent bond length in H2 molecule is the distance between the two nuclei. • Assuming that the two hydrogen atoms are two balls in contact with each other, the radius of each ball would be then half the bond length. Bond Length BL= rH+rH Similarly for other elements, Cl2, Br2…. BL can be measured experimentally:BL → covalent atomic radius II/

  2. Factors affecting the atomic size: • n of the outermost electrons • Attraction force exerted by nucleus on outermost electrons Effective nuclear charge Zeff: charge of nucleus felt by outermost electrons. Electron doesn’t feel the total charge of nucleus because it is screened by inner shells electrons. Thumb rule: Zeff= Z - no. of core electrons n=2 1e- In Li : Zeff=3-2=+1 n=1 2e- 3+ Valence electrons: electrons in outermost shell (last n) Core electrons: the remaining electrons. II/

  3. n constant r ↓ Zeff↑ Zeff constant n ↑ r ↑ II/

  4. II/

  5. Ionic radius 1e- Li+ : 1s2 Li : 1s2 2s1 2e- Highest energy electron removed 3+ Metals tend to lose electrons forming cations. e- 7e- 2e- F : 1s2 2s2 2p5 F- : 1s2 2s2 2p6 9+ Electron added in next vacant orbital Non-metals tend to gain electrons forming anions. • Increased repulsion between electrons • Electrons more apart from each other • Increased volume II/

  6. Cations are smaller than corresponding atoms. • Anions are larger than corresponding atoms. II/

  7. Due to increased attraction Larger nuclear charge II/

  8. Transition metal cations • s-electrons removed before the d-electrons!!!!!! Sc3+ : Ti2+ : V3+ : Cr3+ : Mn2+ : Fe3+ : Co3+ : Ni2+ : Cu+ : Zn2+ : Find the electron configuration for: Cu2+, Ti4+, Fe2+, V2+, Co2+, Cr2+, Mn3+. II/

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