CHEM1001 2014-J-6 June 2014 22/01(A) • Complete the Following Table. the Central Atom Is Underlined. 8 Species Lewis Structu

Home , Barium bromide

CHEM1001 2014-J-6 June 2014 22/01(a) Marks • Complete the following table. The central atom is underlined. 8 Species Lewis structure Molecular geometry

NH3 trigonal pyramidal

SO3 trigonal planar

ICl3 T-shaped

– ICl4 square planar

CHEM1001 2013-J-2 June 2013 22/01(a) Marks • Complete the following table, including resonance structures where appropriate. The 10 central atom is underlined. Is the species Species Lewis structure Molecular geometry polar?

N F F F F NF3 Yes F N F Trigonal pyramidal

S SO O S O O O Yes 2 V-shaped

F F F F F F Cl ClF5 Yes Cl F F F F

Square-based pyramidal

H H B H

BH3 B H No H H Trigonal planar THE REMAINDER OF THIS PAGE IS FOR ROUGH WORKING ONLY

CHEM1001 2012-J-3 June 2012 22/01(a) Marks • Complete the following table, including resonance structures where appropriate. The 6 central atom is underlined. Is the molecule Species Lewis structure(s) polar?

COCl2 yes

CS no 2

NBr3 yes

SO2 yes

• What is resonance? Give at least one example. 2

When two or more Lewis structures can be drawn for a molecule, the true structure is none of the structures that is drawn, but a type of average made up of all the resonance contributors. Some structures may contribute more than others.

– For example, in NO3 , the ion does not contain 1 double and 2 single bonds, but is an average of the three structures shown. All of the N-O bonds are exactly the same length and the energy of the true structure is lower than the theoretical energy for any one of the given structures. This energy difference is known as resonance stabilisation energy.

CHEM1001 2012-J-5 June 2012 22/01(a)

The -bonding in two plausible structures of ozone, O , is shown below. Complete • σ 3 3 each structure by adding electrons and/or π-bonds as appropriate.

Which of these geometries does ozone adopt? Give reasons for your answer.

Ozone adopts the non-cyclic structure. The cyclic structure is very strained with bond angles of 60° instead of 109.5°, making it very unstable. In contrast, the second structure is stabilised by resonance.

Ozone does not contain 1 double and 1 single bond. Both the O-O bonds are exactly the same length and true structure is a sort of average of the two Lewis structures shown. The energy of the true structure is lower than the theoretical energy for either of the given structures. This energy difference is known as resonance stabilisation energy.

CHEM1001 2010-J-3 June 2010 22/01(a) Marks • Complete the following table. 6

Molecule NH 3 SF 4 CO 2

Number of bonding 3 4 4 electron pairs

Number of non- bonding electron 1 1 0 pairs on central atom

Lewis structure H N H O CO H

Molecular shape trigonal pyramidal “see saw” linear

• What is resonance? Illustrate your answer by using the nitrate ion, NO –, as an 3 3 example.

– In NO 3 , the ion does not contain 1 double and 2 single bonds, but is an average of the three structures shown. All of the N-O bonds are exactly the same length and the energy of the true structure is lower than the theoretical energy for any one of the given structures. This energy difference is known as resonance stabilisation energy.

CHEM1001 2010-J-3 June 2010 22/01(a)

CHEM1001 2009-J-3 June 2009 22/01(a)

• Marks Complete the following table. 10 Arrangement of the Geometry of Species Lewis structure electron pairs around species the underlined atom

H N H NH3 tetrahedral trigonal pyramidal H

F F F SF6 S octahedral octahedral F F F

F – BF4 F B F tetrahedral tetrahedral F

CO linear linear 2 O CO

Cl trigonal ICl T-shaped 3 Cl I bipyramidal Cl

CHEM1001 2008-J-3 June 2008 22/01(a) Marks • Complete the following table. 9

Molecular formula NH 3 PCl 5 BrF 3

phosphorus bromine Name ammonia pentachloride trifluoride

Cl F H N H Cl Lewis structure Cl P F Br H Cl Cl F

Number of bonding electron pairs on 3 5 3 central atom Number of non- bonding electron 1 0 2 pairs on central atom

trigonal Molecular shape trigonal pyramidal ‘T-shaped’ bipyramdial THE REMAINDER OF THIS PAGE IS FOR ROUGH WORKING ONLY

CHEM1001 2007-J-3 June 2007 22/01(a) Marks • Complete the following table. 9

Molecular formula SF 6 ClF 3 NH 3

Name chlorine trifluoride

F F F F H N H Lewis structure S F Cl F F H F F

Number of bonding electron pairs on 6 3 3 central atom Number of non- bonding electron 0 2 1 pairs on central atom

Molecular shape octahedral T-shaped trigonal pyramidal

CHEM1001 2004-J-3 June 2004

Marks

 Give the formula and name of a binary ionic compound formed from the following 6 elements. Formula Name magnesium and oxygen MgO magnesium oxide

barium and bromine BaBr2 barium bromide

sodium and nitrogen Na3N sodium nitride

potassium and oxygen K2O potassium oxide 2  Explain why some ionic compounds are soluble in water and usually insoluble in hydrocarbon solvents such as kerosene.

When an ionic solid dissolves, the strong ionic bonds between the constituent ions need to be broken (lattice enthalpy). In water, strong bonds are formed between the ions and the highly polar water molecules to give aquated ionic species. The energy released in this process (enthalpy of solvation) is sufficient to overcome the lattice enthalpy and the solid dissolves. In kerosene, there is little attraction between the ions and the non-polar solvent. The solvation enthalpy is very small in this case, certainly not large enough to overcome the lattice enthalpy, and so dissolution does not occur.

4  Draw Lewis diagrams for the following species. Show both bonding and non- bonding pairs of valence electrons. Give the geometry of the species.

+ NH4 SO2

H O S O

N N H

Geometry: tetrahedral Geometry: bent (~120°)

CHEM1001/CHEM1101 combined 2003-N-5 November 2003

Marks  The structure of morphine is given below. 5

#1 CH3 N a

b #2

#3 O c HO #4 OH

Name the functional groups in morphine that have been highlighted by the boxes. a = amine (3°) b = alkene c = alcohol

What are the approximate bond angles at the labelled atoms?

Atom Bond angles

#1 N ~109.5°

#2 C ~120°

#3 C ~109.5°

#4 O ~109.5°