chap 4 and 5 Flashcards

Question

does simple molecules have low or high melting and boiling point?

Answer 1

molecules with simple molecular structure evaporate easily and are described as volatile. they exist mostly as gases or liquids at room temperature. these molecules have simple molecular structure. small amount of energy is needed to overcome the weak intermolecular forces of attraction the size of the molecule will affect the melting and boiling point. as the molecule gets larger, the intermolecular forces of attraction are stronger and hence more energy is required to overcome them. hence, larger molecules have higher melting and boiling points than smaller molecules

Answer 2

insoluble in water but soluble in organic solvents e.g. alcohol, acetone, benzene

Answer 3

most substances with simple molecular structure exist as molecules and do not have mobile ions or electrons to conduct electricity some substances might dissociate in water to form aqueous solutions that can conduct electricity, for example, hydrogen chloride gas dissolving in water to form hydrochloric acid (presence of mobile H+ and cl- ions)

Answer 4

each carbon atom forms covalent bonds with four other carbon atoms. diamond has a three-dimensional network structure in a tetrahedral structure

Answer 5

each carbon atom forms covalent bonds with three other carbon atoms. graphite has a layered structure consisting of hexagonal rings of carbon atoms

Answer 6

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

Answer 7

molecules with giant covalent structure have numerous covalent bonds holding many atoms together, making them very rigid and able to withstand large forces (e.g. diamond)

Answer 8

graphite’s structure consists of strong covalent bonds between atoms within each layer, but weak intermolecular forces of attraction between the layers of carbon. hence, layer of carbon atoms can slide past each other , but each layer is hard to break apart

Answer 9

diamond is hard and is often used to coat drill bits and cutting tools. giant covalent structures are hard. large amount of energy is needed to break the strong covalent bonds between atoms in diamond graphite is soft and slippery, and is used in solid lubricant and pencil lead. small amount of energy is needed to overcome the weak intermolecular forces of attraction between layers of carbon atoms. the layers of carbon atoms can slide over each other easily

Answer 10

molecules with giant covalent structure are very resistant to heat and are solids at room temperature. the molecules have giant covalent structure. large amount of energy is needed to break the strong covalent bonds between atoms

Answer 11

insoluble in water and organic solvents

Answer 12

molecules with giant covalent structure, like diamond and silicon dioxide, have no mobile electrons or mobile ions and hence do not conduct electricity. however, in graphite, each carbon atom is bonded to three pother carbon atoms. this leaves one unbonded delocalised electron per carbon atom. hence the presence of mobile electrons allow graphite to conduct electricity

Answer 13

metal atoms are held strongly together by metallic bonding. in the solid state, metal atoms are closely packed in an orderly manner. these atoms form a giant metallic lattice structure. the metal atoms lose their outermost electrons to become positively-charged ions (cations). the electrons are now said to be delocalised. the delocalised mobile electrons can move around freely between the metal cations

Answer 14

metallic bonds are the strong electrostatic forces of attraction between positively-charged ions (cations) in the metal and “sea of delocalised mobile electrons”

Answer 15

malleable: can be hammered, bent and flattened into a thin sheet ductile: can be pulled into a wire without breaking

Answer 16

pure metals have a regular structure. if enough force is applied, the layers of atom can slide over one another easily, without disrupting the metallic bonding

Answer 17

pure metals have a regular structure. if enough force is applied, the layers of atom can slide over one another easily, without disrupting the metallic bonding

Answer 18

metals have a high melting and boiling point. metals are typically solids at room temperature and pressure. metals have a giant metallic lattice structure. large amount of energy is needed to overcome the strong electrostatic forces of attraction between positively-charged ions and “sea of delocalised mobile electrons”

Answer 19

metals are good conductors of heat. in the metallic lattice, the ions are closely packed. the proximity of the ions allow them to transfer heat energy by vibration quickly from one ion to another. the movement of mobile electrons further speed up the rate of transfer of heat. hence, metals are good conductors of heat

Answer 20

metals conduct electricity in molten and solid state. in solid or molten state, the electrons are free to move about. hence the mobile electrons enable metals to conduct electricity

Answer 21

an alloy is a mixture of a metal with one or more other elements. the elements can be metals or non-metals

Answer 22

brass (copper and zinc) stainless steel (iron, chromium nickel and carbon)

Answer 23

-to improve the appearance of metals -make metals harder and stronger -lower the melting points of metals: alloys are mixtures that melts over a range of temperatures -make metals more resistant to corrosion

Answer 24

compared to pure metals which are soft as the layers of atoms that are orderly arranged can slide over each other easily, alloys are harder and stronger. in alloys, the additional metal / non-metal atoms of different sizes disrupts the orderly arrangement of atoms in the pure metal, making it difficult for layers of atom to slide over one another. this makes alloys much stronger and harder