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CAIE A-Level Chemistry AS 3.7 Dot and Cross Diagrams Questions

Practise representing ionic, covalent and coordinate bonding with outer electrons, lone pairs, charges and electron origins.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Exam points

  • use different symbols consistently to show electrons from different atoms and show outer electrons only
  • include every bonding pair, lone pair and unpaired electron required by the species
  • enclose ions in brackets with charges and show both ionic and coordinate bonding when present

Covered syllabus points

3.7.1—Dot-and-cross diagrams to illustrate ionic,

Question 1

[Maximum number: 1]

In which species does the underlined atom have an incomplete outer shell?

A

BF3\mathrm{BF}_{3}

B

CH3−\mathrm{CH}_{3}{ }^{-}

C

F2O‾\mathrm{F}_{2} \underline{\mathrm{O}}

D

H3O‾+\mathrm{H}_{3} \underline{\mathrm{O}}^{+}

Question 2

[Maximum number: 1]

In which species is there a lone pair of electrons?

A

CH3\mathrm{CH}_{3}

B

CH3+\mathrm{CH}_{3}{ }^{+}

C

CH3−\mathrm{CH}_{3}^{-}

D

CH4\mathrm{CH}_{4}

Question 3

[Maximum number: 1]

Which molecule has an equal number of bonding electrons and lone-pair electrons?

A

BH3\mathrm{BH}_{3}

B

CO2\mathrm{CO}_{2}

C

F2O\mathrm{F}_{2} \mathrm{O}

D

SO2\mathrm{SO}_{2}

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