Unit 1- Bonding

Question 1

Define giant structures

Answer 1

• network of strong bonds which links all the atoms and ions
• The bonds results in giant structures

Question 2

Define simple molecular structures?

Answer 2

• Small group of atoms
• Intramolecular forces are strong but intermolecular are weak therefore easily spererated

Question 3

Define a lattice

Answer 3

• regular arrangement of atoms or ions in crystals

Question 4

Define polarisation

Answer 4

The distortion of the electron cloud by the cation

Question 5

What are the physical properties of ionic comounds?

Answer 5

• Hard crystaline substances
• High melting and boiling temperatures
• Often soluble in polar solvents
• Does not conduct electricity when solid state

Question 6

What is ionic bonding in a crystal?

Answer 6

• Ionic crystals formed when metals react with non metals
• They are giant lattices
• Strong net electrostatic force due to the negative and positive ions in all directions

Question 7

What is the trends in atomic radii of ionic compounds?

Answer 7

• Positive ions radius are smaller than the atomic radius of the element. Due to a loss in an electron shell
• Negative ions radius is larger than the atomic radius of the element. Due to more electrons added in the outer shell

Question 8

What are the stages involved in forming an ionic compound from its elements?

Answer 8

• Seperate atoms (enthalpy change of atomisation)
• Remove electrons to form ions ( first ionisation energy)
• Add electrons to form ions ( first electron affinity)

Question 9

Where does the energy come from in a Born-Haber cycle?

Answer 9

• Energy is released from the oppositely charged ions join together to form a crystal lattice

Question 10

How are theoretical values calculated ?

Answer 10

• ​Uses laws of electrostatics that assume the bonding is purely ionic

Question 11

What are experimental values?

Answer 11

• Experimental lattice energy calulcated from the Born-Haber cycle

Question 12

What does a difference in the experimental and theoretical value imply?

Answer 12

• Small difference means the bonding is mostly ionic
• If the bonding is stronger and a bigger difference in the values, there is a degree of covalency

Question 13

What does polarisation lead to?

Answer 13

• Electron sharing- degree of covalency

Question 14

What affects the polarising power of the positive metal ion (cation)

Answer 14

• Charge
• Radius

Question 15

What affects the polarisability of a negative non metal ion (anion)

Answer 15

• Charge- Larger the negative charge, more polarisability
• Size- Larger the ion, more polarisability

Question 16

Is enthalphy change of formation exothermic or endotermic for ionic compounds?

What does this mean?

Answer 16

• ​Exothermic
• Compounds are more stable, due to a lower level energy

Question 17

How can enthalpy of formation be calculated for ions that do not exist?

Answer 17

Born-Haber cycle

Question 18

What gives an ion more preference to be formed ?

Answer 18

• More exothermic enthalpy change of formations
• More stable
• Greater preference

Question 19

What is a covalent bond?

Answer 19

• Sharing of electrons between two non metals
• Forms molecules and giant structures
• Electrostatic force between the positive nuclei and the shared pair of electron holds the atoms together

Question 20

What evidence is there for the strength of covalent bonds?

Answer 20

• Giant molecular structures form atomic crystals. The lattice contains covalent bonds where the lattice has a very high melting and boiling temperature therefore the bonding is strong
• Electron denstiy maps of simple covalent structures are directional. Allows for repulsion to shape the molecule showing the strength of the covalent bond

Question 21

What are dative covalent bonds?

Answer 21

When one atom provides both the electrons for the covalent bond. There is no difference in strength or length of the bond

Question 22

What is the general metal structure?

Answer 22

• Positive metal ions in a crystal surrounded by a sea of delocalised electrons
• Close packing
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Question 23

What is metallic bonding?

Answer 23

• The attraction between the positive metal ions and the sea of delocalised electrons

Question 24

What are the properties of metals?

Answer 24

• High melting and boiling temperatures- Strong metallic bonding due to metallic bonding and the close packing therefore emore energy required to break the bonds
• Good conductors of heat and electricity- Heat energy is transffered to the electrons allowing a greater KE for the electrons to conduct the heat and electricity around the metal
• Malleable- Due to delocalised electrons