3.1.3 Bonding

Question 1

What is ionic bonding?

Answer 1

A type of chemical bonding that involves the electrostatic attraction between charged ions

Question 2

Structure of ionic compound

Answer 2

Ions arranged in lattice

Question 3

How happens during ionic bonding?

Answer 3

Outer shell electrons are transferred from metal atoms so non-metal atoms forming ionic bonds (metal cations and non-metals anions)

Question 4

Properties of ionic compounds

Answer 4

Electrical conductivity- not when solid, when molten or dissolved (ions free to move + carry charge)
Melting/boiling point- high due to strong electrostatic forces so a lot of energy is required to overcome
Solubility in water- usually yes as water molecules are polar (part has small negative charge and part has small positive charge) so the water molecules pull metals away from ions + cause it to dissolve

Question 5

How to work out formula of ionic compound

Answer 5

Work out how many electrons need to be lost or gained to form full outer shells (group number). Balance so that the number of electrons that need to be lost from a metal = number of electrons that need to be gained by a non-metal

Question 6

How to form out formula of ions

Answer 6

Look at the group number of that element which indicates the amount of electrons in the outer shell. Use this to work out how many electrons need to be lost or gained to form a full outer shell. If it gains electrons, an anion is formed and if it loses electron, a cation is formed. The amount of electrons required indicates the size of the charge

Question 7

Define the term elecronegativity

Answer 7

The power of an atom to attract a pair of electrons in a covalent bond

Question 8

Explain how permanent dipole-dipole forces arise between hydrogen chloride molecules

Answer 8

Difference in electrogenativity leads to attraction between slight positive on one molecule and slight negative on the other.

Question 9

Explain why sodium bromide has a melting point that is higher than that of sodium and higher than that of sodium iodide

Answer 9

Sodium bromide and iodide ionically bonded
Sodium atom donates 1 electron to bromine/iodine atom creating 2 oppositely charged ions.
The oppositely charged ions are electrostatically attracted and held together in a giant lattice
Sodium is metallically bonded by the electrostatic attraction between positive metal ions and delocalised electrons.
Sodium has a giant lattice structure
Ionic bonds are stronger than metallic bonds (stronger electrostatic attraction)
Br- is smaller than I-

Question 10

What type of substance is an alloy?

Answer 10

Mixture

Question 11

Describe a safe method for making pure crystals of copper sulfate from copper carbonate and dilute sulfuric acid

Answer 11

• sulfuric acid in beaker (or similar)
• add copper carbonate one spatula at a time
• until copper carbonate is in excess or until no more effervescence occurs *
• filter using filter paper and funnel
• filter excess copper carbonate
• pour solution into evaporating basin / dish
• heat using Bunsen burner
• leave to crystallise / leave for water to evaporate / boil off water
• decant solution
• pat dry (using filter paper)
• wear safety spectacles / goggles

Question 12

Suggest why the electronegativity of the elements increases from lithium to fluorine.

Answer 12

More protons
Similar shielding

Question 13

Suggest the type of crystal shown by OF2

Answer 13

Molecular

Question 14

State how the bond between ammonia and boron trichloride is formed

Answer 14

Lone pair is donated to B(Cl3)

Question 15

Why do metals melt over a larger temperature range than simple molecular molecules ?

Answer 15

Metals has forces of attraction in liquid

Question 16

Explain how the value of the Cl-Al-Cl bond angle in AlCl3 changes, if at all, on
formation of the compound H3NAlCl3

Answer 16

Aluminium now surrounded by 4 electron pairs
Tetrahedral
Cl-Al-Cl bond angle decreases

Question 17

Which elements can be hydrogen bonded

Answer 17

Nitrogen
Oxygen
Fluorine

Question 18

Describe what happens when a reaction mixture is refluxed and why it is necessary.

Answer 18

A mixture of liquids is heated to boiling point for a prolonged time
Vapour is formed which escapes from the liquid mixture, is changed back into liquid and returned to the liquid mixture

Question 19

Describe how you would obtain a sample of ethanal from a mixture of three compounds (higher bps). Include in your answer a description of the apparatus you would use and how you would minimise the loss of ethanal

Answer 19

Mixture heated in a suitable flask / container
With still head containing a thermometer Water cooled condenser connected to the still head and suitable cooled collecting vessel
Collect sample at the boiling point of ethanal
Cooled collection vessel necessary to reduce evaporation of ethanal

Question 20

Explain why methanol is easy to liquefy

Answer 20

Hydrogen bonding
Strong enough force to keep molecules together in a liquid

Question 21

Importance of hydrogen bonding in ice

Answer 21

Low density
Spacing of molecules (move further apart)
Ice can float
Increasing melting boiling point

Question 22

Define macromolecular

Answer 22

Giant molecule with covalent bonds

Question 23

Why does macromolecule have higher boiling point than simple molecules

Answer 23

M- contains covalent bonds that must be broken, strong bonds
S- contains VdW between molecules, weak forces

Question 24

Describe the structure of and bonding in graphite and explain why the melting point of graphite is very high

Answer 24

Arranged in layers
Giant covalent
Strong covalent bonds
VdW between layers

Question 25

Bond formed when H+ ion reacts with H2O + how

Answer 25

Dative
Lone pair of electron on O shared/donated to H+

Question 26

Strongest IMF between 2 ammonia molecules

Answer 26

Large difference in electronegativity between N and H
Forms dipole (N partially - and H partially +)
Lone pair on N attracts H partially +

Question 27

Why does NH3 have higher boiling point than AsH3

Answer 27

NH3 contains hydrogen bonding- strongest IMF
AsH3 contains VdW- weakest IMF
Hydrogen bonding stronger than VdW

Question 28

How does hydrogen bonding cause anomalous melting and boiling points of some compounds

Answer 28

Hydrogen bonding is the strongest intermolecular force so the boiling/melting point will be higher than expected if present

Question 29

You can describe bonding pairs and lone pairs of electrons as

Answer 29

Charge clouds that repel each other

Question 30

How do pairs of electrons in the outer shell arrange themself

Answer 30

As far apart as possible to minimise repulsion

Question 31

Suggest one reason why electron pair repulsion theory cannot be used to predict the
shape of the [CoCl4]2– ion

Answer 31

Too many electrons in d sub-shell

Question 32

3 factors affecting electronegativity

Answer 32

Nuclear charge
Atomic radius
Electron shielding

Question 33

Describe Van der Waals forces of attraction

Answer 33

Temporary dipoles created by the random movement of electrons
Induces dipole in neighbouring molecule
Temporary induced dipole-dipole attraction

Question 34

Why are Van der Waals forces stronger in larger molecules

Answer 34

More electrons

Question 35

How does hydrogen bonding arise

Answer 35

O-H, N-H, F-H bonds
Lone pairs of electrons on O,N,F
Highly electronegative
Leave H nucleus exposed
Strong force of attraction between H nucleus and lone pair on O,N,F

Question 36

Why is ice less dense that liquid water

Answer 36

In water, hydrogen bonds constantly break + reform as molecules move about
Ice, hydrogen bonds hold molecules in fixed positions. Makes them slightly further apart than in liquid water

Question 37

Electron repulsion theory

Answer 37

Electron pairs will take up positions as far away from each other as possible to minimise the repulsive forces between them