[SEC 3] CHAPTER 5 - structure & properties of materials

Question 1

what is a compound made of?

Answer 1

two or more elements that are chemically combined

Question 2

what is a mixture made of?

Answer 2

two or more elements and/or compounds that are not chemically combined

Question 3

how is an element formed?

Answer 3

most naturally occuring

Question 4

how is a compound formed?

Answer 4

from a chemical reaction

Question 5

how is a mixture formed

Answer 5

usually from physical mixing

Question 6

what is the ratio of a compounds constituents?

Answer 6

fixed ratio (doesnt change)

Question 7

what is the raio of a mixtures constituents?

Answer 7

no fixed ratio

Question 8

what are a compounds properties like?

Answer 8

has different properties from its constituents elements

Question 9

what are a mixtures properties like?

Answer 9

usually has similar properties to its constituent suubstances

Question 10

melting and boiling points of elements

Answer 10

fixed (pure)

Question 11

melting and boiling points of compound

Answer 11

fixed (pure)

Question 12

melting and boiling points of mixture

Answer 12

melt and boil over a range of temperatures (impure)

Question 13

what is a molten state

Answer 13

solid is heated to HIGH temperature until liquuid state
EG. sodium

Question 14

what is aqueous state

Answer 14

when a solid is DISSOLVED in water
EG. sodium

Question 15

what is Van Der Waals

Answer 15

intermolecular forces of attraction

Question 16

what is the structure of diamond, graphite and silicon dioxide?

Answer 16

giant covalent molecule

Question 17

what is the structure of hydrogen (H2), bromine (Br2) and iodine (I2)?

Answer 17

simple covalent molecule

Question 18

what are giant covalent molecules called?

Answer 18

macromolecules

Question 19

define allotropes

Answer 19

allotropes are different forms of the same element with different structural arrangement of atoms

Question 20

What are the allotropes of carbon and describe its structural arrangement

Answer 20

1. Diamond
   - in a tetrahedral arrangement
2. Graphite
   - is made of layers of carbon atoms in a hexagonal arrangement

Question 21

what are the structural properties of diamond?

Answer 21

• diamond is a macromolecule made up of carbon atoms
• each carbon atom forms covalent bonds with four other carbon atoms
• has a 3D network structure called tetrahedral arrangement
• contains millions of carbon atoms formed by strong covalent bonds

Question 22

why do giant covalent molecules have high melting and boiling points?

Answer 22

because many strong covalent bonds require large amounts of energy to overcome

Question 23

why diamond cannot conduct electricity?

Answer 23

because all valence electrons are used for covalent bonding, therefore no mobile electrons to carry electrical charges

Question 24

why graphite can conduct electricity?

Answer 24

because there are mobile delocalised electrons (free to move along the layers of carbon atoms)

Question 25

why giant covalent molecules insoluble in both water and organic solvents?

Answer 25

because attraction between the solvent molecules and giant molecular structure are not strong enough to break the strong covalent bonds

Question 26

what are the attractive forces between particles in giant covalent molecules?

Answer 26

strong covalent bonds, except for weak intermolecular forces of attraction between layers of graphite

Question 27

why is diamond/silicon dioxide hard?

Answer 27

hard because of strong covalent bonding in all directions therefore atoms cannot slide past each other

Question 28

why is graphite slippery and soft?

Answer 28

because weak intermolecular forces of attraction between the layers allow layers to slide over each other easily

Question 29

why simple covalent molecules have low melting and boiling points?

Answer 29

because weak intermolecular forces of attraction require small amount of energy to overcome the larger the size of the molecule, the higher the molecular surface area, the stronger the Van Der Waals focres, the higher the melting and boiling point

Question 30

why giant ionic crystal lattice have high (usually more than 500degrees) melting and boiling points?

Answer 30

because strong electrostatis forces of attraction between oppositely charged ions require large amount of energy to overcome the higher the charged of the ions, the higher the melting and boiling point

Question 31

why giant ionic crystal lattice in solic state cannot conduct electricity?

Answer 31

because ions are not mobile, they are held in fixed positions and cannot move around to carry electrical chargesy

Question 32

giant ionic crystal lattice can connduct electricity in molten and aqueous state?

Answer 32

because there are mobile ions to carry electrical charges

Question 33

why simple covalent molecules cannot conduct electricity in physical state?

Answer 33

because there are no mobile electrons and ions to carry electrical charges

Question 34

what is the solubility of giant ionic crystal lattice?

Answer 34

usually soluble in water and insoluble in organic solvents

Question 35

why giant covalent molecules insoluble in both water and organic solvents?

Answer 35

because attraction between the solvent molecules and giant molecular structure are not strong enough to break the strong covalent bonds

Question 36

why giant ionic crystal lattice is hard?

Answer 36

because strong electrostatic forces of attraction between oppositely charged ions make ionic compounds resistant to deforming difficult for layers of ions to slide over each other

Question 37

what particles is giant metallic lattice made up of?

Answer 37

lattice of positive ions surrounded by sea ood delocalised electrons

Question 38

why giant metallic lattice have high melting and boiling points?

Answer 38

because strong electrostatic forces of attraction between positive ions and sea of delocalised electrons require large amount of energy to overcome

Question 39

why giant metallic lattice can conduct electricity in solid state?

Answer 39

because there are mobile/delocalised electrons to carry electrical charges

Question 40

what is the solubility of giant metallic lattice?

Answer 40

insoluble in both water and organic solvents

Question 41

why is giant metallic lattice malleable and ductile?

Answer 41

due to regular packing of same-sized atoms, layers of atoms can slide over each other easily when a force is applied