atomic structure + bonding

Question 1

Bonding of ionic compounds

Answer 1

Ionic bonds are strong electrostatic forces of attraction between opposite charged ions

Question 2

Structure of ionic compounds

Answer 2

Ions in an ionic compound form a lattice structure:
-regular arrangement of ions
-ionic bonds between oppositely charged ions

Question 3

M.p and b.p of ionic compounds

Answer 3

High
Solid at room temperature:
-many strong ionic bonds
-large amounts of energy must be -transferred to break structure

Question 4

What is the solubility of ionic compounds in water ?

Answer 4

Ionic compounds often soluble in water - dissolve to form aqueous solutions

Question 5

What are ionic lattices referred to ?

Answer 5

Called ‘giant lattice’ as involves many ions

Question 6

Where can covalent bonds occur (singular)

Answer 6

Covalent bonds occur in a single element - group number

Question 7

Properties of covalent bonds NOT SIMPLE MOLECULAR SUBSTANCES

Answer 7

-strong
-between non metals
-produce molecules

Question 8

Bonding of SIMPLE COVALENT SUBSTANCES

Answer 8

Simple molecule made up of few atoms joined by strong covalent bonds :
-non metal compounds (HCL,CH4)
-non-metal elements (H2, O2)
Usually have low mp and BP so liquid or gas at room temperature

Question 9

Intermolecular forces / difference between them and covalent bonds

Answer 9

Weak attractive forces between molecules called intermolecular forces - when simple molecular substance melts or boils :
-intermolecular forces overcome
-covalent bonds do NOT break

Question 10

Do simple molecular substances conduct ?

Answer 10

Do not conduct as - not electrically charged and do NOT contain electrons that are free to move
SOME however break down in a solution, forming ions that can move - solution can therefore conduct

Question 11

Do simple molecular substances dissolve in water ?

Answer 11

MANY simple molecular structures insoluble in water - intermolecular forces between water and substances weaker than those between
-water molecules
-molecules of the substance

Question 12

What are the conditions for solubility ? (Simple molecular structures)

Answer 12

Only of they can form strong enough intermolecular forces with water molecules e.g.
-hydrogen + water sparingly soluble
-chlorine, carbon dioxide, sulfur dioxide and ammonia soluble
-ethanol and ethanoic acid soluble
-sugar soluble in water

Question 13

Example - explain why nitrogen is suitable for use as an insulator in high voltage electrical transformers

Answer 13

Unreactive - does not react with materials in transformer. Can insulate as does not conduct electricity

Question 14

What is bonding and structure like in a giant molecular structure?

Answer 14

Giant molecules consists of many atoms :
-joined by strong covalent bonds
-arranged in a regular lattice structure
-Can be non metal elements e.g. carbon or compounds such as silicone

Question 15

What is the melting and boiling points of giant molecular compounds ?

Answer 15

-High mp+bp so solids at room temp. Lots of energy transferred to break the MANY strong covalent bonds

Question 16

What is the solubility of giant molecular substances ?

Answer 16

Insoluble in water

Question 17

How do we represent giant molecular substances ?

Answer 17

Because there are many atiks you cannot represent an entire giant molecule using displayed formulae or dot and cross diagrams

Question 18

Arrangement of diamond

Answer 18

-each atom bonded to four others
-strong covalent bonds between atoms
-hexagonal shape
-form of carbon

Question 19

Arrangement of graphite

Answer 19

-Each atom bonded to 3 others
-weak intermolecular forces between layers
-strong covalent bonds between atoms in a layer

Question 20

Uses of graphite

Answer 20

In graphite, the weak intermolecular forces let the layers slide over each other - useful as a lubricant + slippery

Question 21

(WORKED EXAMPLE)
Graphite is used to make electrodes because it contains electricity. Explain why it conducts electricity but diamond does not ?

Answer 21

A carbon atom can form four covalent bonds - in graphite each carbon atom only forms 3 covalent bonds. The non binding outer electrons become delocalised meaning they can move through the structure, so graphite can conduct. Diamond does not have delocalised electrons so cannot conduct.

Question 22

What is the structure of graphene / how is it represented ?

Answer 22

Graphene resembles a single later of graphite:
-each carbon atom is covalently bonded to three other carbon atoms
-it has a regular lattice structure
-interlocking hexagonal rings of carbon atoms

Question 23

What are the properties of graphene ?

Answer 23

-conducts electricity because non bonding outer electrons become delocalised and can move through the structure
-is STRONG and FLEXIBLE as contains many strong covalent bonds
-is almost transparent as its layers are just one atom thick

Question 24

What is a fullerine ?

Answer 24

Fullerenes resemble a sheet of graphene rolled

Question 25

What are buckyballs ? (Fullerene)

Answer 25

Hollow balls.
Buckminsterfullerene has carbon atoms arranged in pentagons as well as hexagons.
Materials made from buckyballs :
-conduct electricity as have delocalised electrons
-are soft when solid because they have weak intermolecular forces

Question 26

What are nanotubes ? (Fullerene)

Answer 26

Hollow tubes with open or closed ends. They can be several mm long.
-conduct as have delocalised electrons
-strong because the structure is made of many strong covalent bonds

Question 27

Poly(ethane) misconception

Answer 27

Poly(ethane) is not a fullerene but a hydrocarbon. Polymer molecules describes as macromolecules rather than giant covalent structures

Question 28

(WORKED EXAMPLE) describe the structure of poly(ethane)

Answer 28

Consists of large molecules containing chains of carbon atoms these atoms are joined together and to hydrogen atoms by covalent bonds.

Question 29

Properties of metals (reshaping)

Answer 29

Malleable- bent into shape without shattering. If force applied layers of ions slide over each other changing the shape of the metal. whereas non metals brittle and will break when bent or hit in the solid state

Question 30

Metallic bonding

Answer 30

Consists of a giant lattice of positively charged metal ions + has a sea of delocalised electrons - come from the outer shells of the atoms.
Metallic bonds are strong forces of attraction between positive metal ions and delocalised electrons

Question 31

Solubility of metals

Answer 31

Insoluble in water, however some dissolve - react with water to produce soluble metal HYDROXIDES, (and hydrogen) which dissolve exposing more metal to the water.

Question 32

How do we represent structure and bonding ?

Answer 32

The structure and bonding of different substances are represented using models. (All of which have some limitations)

Question 33

Positives and Limitations of the written formulae

Answer 33

Empirical:
-simplest whole number ratio. This does not show how the atoms are arranged or the actual number of atoms
Molecular:
-number of atoms in an element. Does not show how the atoms are arranged
Structural:
-most accurate as gives example of number of atoms and how they are arranged.

Question 34

Limitations of drawn structures

Answer 34

When you draw a structure you should show all the covalent bonds in a molecule
- does not show molecules three-dimensional shape
-does not show the bonding and non-bonding electrons

Question 35

Positives and Limitations of ball and stick models

Answer 35

Can be drawn or modelled ✅
Do not show ❌
-how each atom is bonded to other atoms
-the molecules three dimensional shape
Do not show the bonding and non bonding electons, or each elements chemical symbol.

Question 36

Positives and Limitations of space filling models

Answer 36

✅more accurate in showing sites if atoms relative to their binds than ball and stick
❌may not see all the atoms in q complex space filling model

Question 37

(WORKED EXAMPLE) Positives and negatives of dot and cross diagrams

Answer 37

✅this diagram shows the symbol for each atom in the molecule. Shows how each atom is bonded to other atoms. Pair of electrons in each covalent bond shown by dots and crosses non bonding pairs of electrons in the outer shells are included.
❌does not show the three dimensional shape of the molecule. May lead you to think that the molecules are flat as two dimensional.

Question 38

Why are covalent bonds strong ?

Answer 38

Covalent bonds are strong because the shared electrons are attracted to the nucleus of both atoms.

Question 39

What is the advantage of double and triple bonds?

Answer 39

Double and triple bonds are normally stronger and require more energy to break.