Topic 2: Elements, Compounds and Mixtures Flashcards
1
Q
What does it mean if a substance is pure?
A
- Consist of a single element or compound which contains no other substances
2
Q
What is a mixture?
A
- Consists of two or more elements or compounds that are physically mixed together, they are not chemically combined.
3
Q
What is the difference in melting and boiling point for pure substances and mixtures?
A
- Pure melt and boil at specific and sharp temperatures
- Mixtures have a range of melting and boiling points as they consist of different substances that tend to lower the melting point and broaden the melting point range
4
Q
What is melting point analysis used for?
A
- Assess purity of drugs
5
Q
What is a cooling curve?
A
- Used to see the influence of impurities
- Horizontal show sharp melting point, pure
- Gradual decrease, impure
6
Q
What is the equation for percentage change?
A
Percentage Change = Final Value - Original Value / Original Value X 100
7
Q
What is the symbol for relative atomic mass?
A
Ar
8
Q
What is the symbol for relative formula mass?
A
Mr
9
Q
What does the relative atomic mass refer to?
A
Average mass of the atoms of an element
10
Q
What does the relative molecular mass refer to?
A
Average mass of the atoms of one molecule of an element or compound
11
Q
What is the empirical formula?
A
Simplest whole number ratio of atoms
12
Q
How do you figure out the empirical formula of a dot-and-cross diagram?
A
Count no. of atoms of each element and simplify
13
Q
How do you figure out the empirical formula of a 3D lattice structure diagram?
A
- Write ions in lattice
- Balance charges
14
Q
What is the equation for the percentage by mass of an element in a compound?
A
% mass of an element = Aᵣ x No. of atoms in element / Mᵣ of compound X 100
15
Q
What is an alloy?
A
Mixture of metals
16
Q
What is steel composed of and used for?
A
- Alloy of Iron + Carbon
- Construction Materials , Appliances, Vehicles
17
Q
What is stainless steel composed of and used for?
A
- Alloy of Iron + Chromium + Nickel
- Kitchen Utensils, Surgical Instruments
18
Q
What is brass composed of and used for?
A
- Copper + Zinc
- Musical Instruments, Plumbing
19
Q
What is bronze composed of and used for?
A
- Copper + Tin
- Sculptures, Medals, Bearings
20
Q
What is duralumin composed of and used for?
A
- Aluminium + Copper + Manganese + Magnesium
- Aircraft Structures, Automotive Parts
21
Q
What is a formulation?
A
A mixture that has been designed as a useful product
22
Q
Why are alloys stronger and harder than most pure metals?
A
- Alloys contain atoms of different sizes, which distorts the regular arrangements of atoms
- This makes it more difficult for the layers to slide over each other
23
Q
What is filtration?
A
- Used to separate undissolved solid from solid liquid solution
- Filter paper placed in filter funnel
- Paper only allows small liquid particles to pass through, the filtrate, and solid particles are remained as residue
24
Q
What is crystallisation?
A
- Used to separate dissolved solid from solution where solid is more soluble in hot compared to cold solvent
- Solution heated, solvent evaporated, saturated solution left behind
- Cool solution slowly and crystals begin to grow
- Filtered than washed with cold distilled water to remove impurities
25
What is simple distillation?
- Separate pure liquid from mixture
- Solution is heated and pure water evaporates
- Vapour passes through condenser, turns into pure liquid and collected in beaker
- Only solid solute left behind
26
What is fractional distillation?
- Used for miscible liquids with different boiling points.
- Selectively evaporating and condensing components based on their boiling temperatures.
27
How does the fractionating column improve separation in fractional distillation?
- Contains glass beads that increase surface area
- Cause substances with higher boiling points to cool and condense within the column
- Allow lower boiling point substances to pass through to the condenser
28
How would ethanol be separated from water using fractional distillation?
- Ethanol-water mixture is heated to 78°C (ethanol's boiling point)
- Ethanol evaporates, passes through the fractionating column, condenses in the condenser, and collects in a beaker
- Heating is stopped before reaching water's boiling point (100°C).
29
What is chromatography?
Used to separate substances and provide information to help identify them
30
Why does paper chromatography work?
Components have different solubilities in the solvent and different adhesion to the paper
31
What does the paper chromatography process involve?
- Drawing a pencil line on chromatography paper (pencil won't run with the solvent)
- Placing sample spots on the line
- Putting the paper in solvent, keeping the pencil line above solvent level
- Letting the solvent travel up by capillary action
32
Why do substance spread apart during paper chromatography?
Different substances have different solubilities so will travel at different rates causing spread
33
What are the two phases in chromatography?
- Mobile Phase
- Stationary Phase
34
What is the mobile and stationary phase in paper chromatography?
- Mobile Phase is solvent in which sample molecules move (water/ethanol)
- Stationary Phase is Chromatography Paper
35
What is the mobile and stationary phase in TLC?
- Stationary Phase is a thin layer of inert substance (silica) supported on flat, unreactive surface
- Mobile Phase is a solvent
36
What are Rf values used for in chromatography?
Rf values are used to identify the components of mixtures
37
How is the Rf value calculated?
Retention factor = distance moved by compound ÷ distance moved by solvent
38
Do Rf values have units?
No
39
What happens to Rf values if the solvent is changed?
The Rf value changes when the solvent is changed
40
Why can Rf values be used to identify unknown substances?
Because the Rf value of a particular compound is always the same under identical conditions, it can be compared with reference values of known substances
41
From where are both distances measured when calculating Rf values?
Both distances are measured from the baseline
42
How many spots will a pure substance produce on a chromatogram?
Pure substances will produce only one spot on the chromatogram
43
What does it mean if two substances produce identical chromatograms?
If two or more substances produce identical chromatograms
44
How can you identify a mixture using chromatography?
A mixture will separate on the paper to show all the different components as separate spots
45
What does a chromatogram with more than one spot indicate?
It indicates an impure substance
46
What is the mobile phase in gas chromatography?
An unreactive carrier gas (e.g.
47
What is the stationary phase in gas chromatography?
A thin layer of an unreactive liquid (e.g.
48
What is meant by 'retention time' in gas chromatography?
How long each component takes to travel through the column
49
What factors affect how quickly substances move through a gas chromatography column?
Their attraction to the stationary phase - substances with more attraction take longer to move through
50
What does the number of peaks on a gas chromatogram represent?
The number of compounds in the mixture
51
What does the height of a peak on a gas chromatogram indicate?
How much of each compound is present (higher peak = more compound)
52
What does the position of a peak on a gas chromatogram indicate?
The retention time of the compound (how long it took to move through the column)
53
How can elements be divided based on their electron behavior?
Elements can be divided into metals and non-metals; metals form positive ions by losing electrons, while non-metals form negative ions by gaining electrons.
54
What is an ion?
An ion is an atom or molecule which has become charged through the loss or gain of one or more electron(s).
55
What happens when metals form ions?
Metals form positive ions (cations) when they react because they lose electrons, leaving them with an overall positive charge.
56
What happens when non-metals form ions?
Non-metals form negative ions (anions) when they react because they gain electrons, leaving them with an overall negative charge.
57
What are metalloids?
Elements that display properties of both metals and non-metals, also called semi-metals.
58
How does metallic character change across the Periodic Table?
Metallic character decreases as you move across a Period from left to right, and increases as you move down a Group.
59
Why does metallic character change in this pattern?
This trend occurs due to atoms more readily accepting electrons to fill their valence shells as atomic size and nuclear attraction changes.
60
How is the Periodic Table organized in terms of periods and groups?
The table is arranged in vertical columns called groups and horizontal rows called periods.
61
What do periods in the Periodic Table represent?
Periods are horizontal rows that show the number of shells of electrons an atom has. For example, elements in Period 2 have two electron shells.
62
What do groups in the Periodic Table represent?
Groups are vertical columns that show how many outer electrons each atom has. For example, Group 4 elements have atoms with 4 electrons in the outermost shell.
63
What are some alternative names for certain groups in the Periodic Table?
Group 1 is also known as the 'alkali metals', Group 7 is also known as the 'halogens', and Group 0 is also known as the 'noble gases'.
64
How do electrons occupy shells in an atom?
Electrons first occupy the shell closest to the nucleus (maximum 2 electrons), then fill additional shells when a shell becomes full.
65
How many electrons can the first three electron shells hold?
The first shell can hold 2 electrons, while the second and third shells can each hold 8 electrons.
66
What is the valence shell?
The outermost shell of an atom is called the valence shell, and an atom is much more stable if this shell is completely filled with electrons.
67
How do atoms achieve a full outer shell of electrons?
Atoms can gain electrons (non-metals), lose electrons (metals), or share electrons (covalent bonds) to achieve a full outer shell.
68
How is electron configuration written using number notation?
By writing the number of electrons in each shell separated by commas or periods, starting with the innermost shell (e.g., 2.8.1 for sodium).
69
What is the relationship between an element's group number and its electron configuration?
Elements in the same group have the same number of outer shell electrons. For example, 2.2, 2.8.2, and 2.8.8.2 all show Group 2 elements as they all end in '2'.
70
What is an ionic bond?
The strong electrostatic forces of attraction between oppositely charged ions, typically occurring between a metal and a non-metal.
71
How is a sodium chloride (NaCl) ionic bond formed?
Sodium loses one electron to form Na+ (1+), and chlorine gains one electron to form Cl- (1-), with the oppositely charged ions attracting each other.
72
How is a magnesium oxide (MgO) ionic bond formed?
Magnesium loses two electrons to form Mg2+ (2+), and oxygen gains two electrons to form O2- (2-), with the oppositely charged ions attracting each other.
73
What are the advantages of dot and cross diagrams for showing ionic compounds?
They are useful for illustrating the transfer of electrons and indicate from which atom the bonding electrons come.
74
What are the disadvantages of dot and cross diagrams for showing ionic compounds?
They fail to illustrate the 3D arrangements of atoms and electron shells, and don't indicate the relative sizes of the atoms.
75
What are the advantages of ball and stick models for ionic compounds?
They are useful for illustrating the arrangement of atoms/ions in 3D space and for visualizing the shape of an ionic compound.
76
What are the disadvantages of ball and stick models for ionic compounds?
They fail to indicate the movement of electrons, show ions placed far apart, don't show accurate ion sizes, don't show electrostatic forces, and don't show ion charges.
77
What is a covalent bond?
When non-metal atoms share pairs of electrons with other non-metal atoms to obtain a full outer shell of electrons.
78
How strong are covalent bonds?
Covalent bonds between atoms are very strong.
79
What is a molecule?
When two or more atoms are chemically bonded together, they form 'molecules'.
80
What types of structures can covalently bonded substances form?
Covalently bonded substances may consist of small molecules or giant structures.
81
What are intermolecular forces?
Weak forces that exist between individual molecules (not to be confused with the strong covalent bonds within molecules).
82
What are bonding electrons?
Shared electrons that occur in pairs and are involved in covalent bonds.
83
What are non-bonding electrons or lone pairs?
Electrons on the outer shell which are not involved in the covalent bond(s).
84
Can simple covalent molecules conduct electricity?
No, simple covalent molecules do not conduct electricity as they do not contain free electrons.
85
What is the difference between simple covalent molecules and giant covalent structures?
Simple covalent molecules contain fixed numbers of atoms bonded with strong covalent bonds and have weak intermolecular forces between molecules. Giant covalent structures have huge numbers of atoms all bonded together with strong covalent bonds with no weak intermolecular forces.
86
What are three common giant covalent structures?
Diamond, graphite, and silicon dioxide.
87
Why do giant covalent structures have high melting and boiling points?
They have many strong covalent bonds, requiring large amounts of heat energy to overcome these forces and break down bonds.
88
Can giant covalent structures conduct electricity?
Most cannot conduct electricity as they do not have free electrons nor charged particles, but there are exceptions such as graphite and graphene.
89
What are polymers?
Very large covalent molecules (macromolecules) made by linking together large numbers of smaller molecules called monomers.
90
How are polymer chains held together?
Each monomer is connected to adjacent units via strong covalent bonds, with intermolecular forces acting between polymer chains.
91
Why are polymers usually solid at room temperature?
The intermolecular forces acting between polymer chains are larger than those between simple molecules.
92
Give examples of synthetic polymers.
Polythene, polyvinyl chloride (PVC), resins, plastics, polystyrene, nylon.
93
Give examples of natural or biological polymers.
DNA, proteins, silk, wool.
94
What is metallic bonding?
A bonding structure where metal atoms lose their outer shell electrons to become positively charged ions, with the electrons forming a 'sea' of delocalised electrons.
95
What are delocalised electrons in a metal?
Outer shell electrons that no longer belong to any specific metal atom and can move freely between the positive metal ions.
96
Why can metals conduct electricity?
Due to the delocalised electrons that can move freely within the structure.
97
How are metal atoms arranged in metallic bonding?
Metal ions are arranged in a regular pattern (lattice structure), with strong electrostatic attractions between the positive metal ions and the negative sea of delocalised electrons.
98
How did Mendeleev organize his Periodic Table?
He organized elements into vertical columns based on their chemical properties, and horizontally in order of increasing atomic mass.
99
What was unique about Mendeleev's approach to the Periodic Table?
He left gaps for undiscovered elements instead of forcing elements to fit, and he switched the order of some elements to maintain consistency in chemical properties down columns.
100
How did Mendeleev predict properties of undiscovered elements?
He used the properties and trends of other elements in the group with the gap to predict the properties of undiscovered elements.
101
Which predicted element confirmed Mendeleev's theory when it was later discovered?
'Eka-silicon', which we now know as germanium.
102
What does the group number on the modern Periodic Table indicate?
The number of electrons in the outer shell (valence electrons), except for helium which has 2 electrons in its first and only shell but is in Group 0.
103
Why do elements in the same group have similar chemical reactions?
Because they have the same number of electrons in their outer shell, which influences how they react.
104
How does reactivity change down Group 1 (alkali metals)?
Group 1 metals become more reactive as you move down the group.
105
How does reactivity change down Group 7 (halogens)?
Group 7 non-metals show a decrease in reactivity moving down the group.
106
How do reactivity trends for metals and non-metals generally compare?
It is common for trends to be the opposite for metals and non-metals.
107
What group in the Periodic Table is carbon found and what abilities does it have?
- Group 4
- Ability to form four covalent bonds
- Large no. of natural and synthetic organic compounds can be formed
108
What are allotropes?
Different forms of the same element
109
Describe diamond
- Allotrope of carbon
- One carbon atom bonds with four other carbons, forming a tetrahedron
- Covalent bonds are identical and strong
- No intermolecular forces
110
What are the physical properties of diamond?
- Doesn't conduct electricity
- High melting point
- Extremely hard
111
What are the uses of diamond?
- Useful for purposes where extremely tough material is required
- Jewellery
- Coating blades in cutting tools
112
Describe graphite
- Allotrope of carbon
- One carbon atom bonds with three others forming layers of hexagons, leaving one free electron per carbon atom
- Free electrons are free to move, carry charge and migrate along layers, hence can conduct electricity
- Covalent bonds are strong, but layers have weak intermolecular forces so layers can slide over other making graphite soft and slippery
113
What are the physical properties of graphite?
- Conducts electricity and heat
- High melting point
- Soft and slippery
114
What are the uses of graphite?
- Pencils
- Industrial Lubricant (engines and locks)
- Inert electrodes for electrolysis
115
Describe graphene
- Single layer of graphite
- Sheet of carbon atoms covalently bonded forming a continuous hexagonal layer
- 2D Molecule
- Useful in fabricating composite materials and in electronics
116
What are the physical properties of graphene?
- Strong and light (Strong covalent bonds)
- Conducts heat and electricity (Free electrons move along surface)
- Transparent (Absorbs 2.3% of light)
- Flexible (Strong covalent bonds between atoms are flexible)
117
Describe fullerenes.
- Group of carbon allotropes which consist of molecules that form hollow tubes or spheres
- Trap other molecules by forming around target molecule
- Useful for drug delivery systems
- Huge SA, useful catalyst
- Excellent lubricants
118
Describe nanotubes.
- Graphene rolled into cylinder
- High tensile strength
- Conduct electricity
119
How does the amount of energy needed to change state relate to the forces between particles?
The amount of energy needed to change state from solid to liquid and from liquid to gas depends on the strength of the forces between the particles.
120
What is the relationship between force strength and energy requirements for state changes?
The stronger the forces of attraction, the more energy that is needed to overcome them for a state change to occur.
121
How do the forces between particles affect melting and boiling points?
The stronger the forces between the particles the higher the melting point and boiling point of the substance.
122
What type of intermolecular forces do simple molecules have and how does this affect their melting and boiling points?
Simple molecules have weak intermolecular forces that need little energy to break resulting in low melting and boiling points.
123
What type of bonds do giant ionic lattices and macromolecular structures have and how does this affect their melting and boiling points?
Giant ionic lattices and macromolecular structures have very strong bonds which need lots of energy to break, resulting in high melting and boiling points.
124
What is melting?
Melting is when a solid (s) changes into a liquid (l).
125
What type of energy does melting require and what happens to the particles?
The process requires heat energy which transforms into kinetic energy, allowing the particles to move.
126
What is special about the temperature at which melting occurs?
It occurs at a specific temperature known as the melting point which is unique to each pure solid.
127
What is boiling?
Boiling is when a liquid (l) changes into a gas (g).
128
What happens during the boiling process?
This requires heat which causes bubbles of gas to form below the surface of a liquid, allowing for liquid particles to escape from the surface and from within the liquid.
129
What is special about the temperature at which boiling occurs?
It occurs at a specific temperature known as the boiling point which is unique to each pure liquid.
130
What is freezing?
Freezing is when a liquid (l) changes into a solid (s).
131
How does freezing relate to melting?
This is the reverse of melting and occurs at exactly the same temperature as melting, hence the melting point and freezing point of a pure substance are the same.
132
What is an example of a freezing/melting point?
Water for example freezes and melts at 0 ºC.
133
What temperature conditions are required for freezing?
It requires a significant decrease in temperature (or loss of thermal energy) and occurs at a specific temperature which is unique for each pure substance.
134
What is evaporation?
When a liquid (l) changes into a gas (g).
135
Where does evaporation occur and how does it differ from boiling?
Evaporation occurs only at the surface of liquids where high energy particles can escape from the liquids surface at low temperatures, below the boiling point of the liquid.
136
What factors affect the rate of evaporation?
The larger the surface area and the warmer the liquid/surface, the more quickly a liquid can evaporate.
137
Over what temperature range does evaporation occur?
Evaporation occurs over a range of temperatures, but heating will speed up the process as particles need energy to escape from the surface.
138
What is condensation?
When a gas (g) changes into a liquid (l), usually on cooling.
139
What happens to gas particles during condensation?
When a gas is cooled its particles lose energy and when they bump into each other, they lack energy to bounce away again, instead grouping together to form a liquid.
140
What is sublimation?
When a solid (s) changes directly into a gas (g).
141
What are examples of substances that undergo sublimation?
This happens to only a few solids, such as iodine or solid carbon dioxide.
142
What is the reverse of sublimation called?
The reverse reaction also happens and is called desublimation or deposition.
143
How can the physical state of a substance be predicted?
The physical state of a substance under certain conditions can be predicted from a given set of data.
144
What data is usually provided to predict a substance's physical state?
Normally you are given melting and boiling point data for a substance and asked to predict its physical state in specified conditions.
145
What state will a substance be in at temperatures below the melting point?
At temperatures below the melting point: The substance will be in the solid state.
146
What state will a substance be in at temperatures between the melting point and the boiling point?
At temperatures between the melting point and the boiling point: The substance will be in the liquid state.
147
What state will a substance be in at temperatures above the boiling point?
At temperatures above the boiling point: The substance will be in the gas state.
148
What are examples of bulk properties?
- Electrical Conductivity
- Melting and Boiling Points
149
How do bulk properties arise?
Many atoms, ions or molecules acting together
150
What is meant by brittle?
Cracks or breaks when an external force is applied
151
What is meant by malleable?
Change shape without cracking or breaking layers
152
What are examples of brittle substances?
Ionic and Giant Covalent Structures
153
What are examples of malleable substances?
Most metals
154
Why are metals malleable?
Atoms are arranged in layers which slide over each other when force is applied
155
Why are Giant Covalent and Ionic structures brittle?
Bonds are broken when force is applied and as a result break
156
What are the forces in polymers?
- Solid at room temp.
- Strong covalent bonds between atoms but intermolecular forces between polymer molecules
157
What are the difference between intermolecular forces and covalent/ionic bonds?
Intermolecular forces are larger than those between simple covalent molecules and therefore need more energy to break but weaker than ionic or covalent bonds.
158
What are the three categories of particles based on diameter?
Coarse particles (particulate-matter or dust), Fine particles, and Nanoparticles
159
What is the size range of nanoparticles?
Between 1 and 100 nanometres
160
How many atoms do nanoparticles typically contain?
Only a few hundred atoms
161
How do nanoparticles compare in size to atoms and simple molecules?
Atoms and simple molecules are around 100 times larger than nanoparticles
162
What is the size range of fine particles?
Between 100 and 2500 nm
163
What is the field of research into the production and application of nanoparticles called?
Nanoscience
164
What is one of the most interesting features of nanoparticles?
Their very high surface area to volume ratio
165
What happens to the surface area to volume ratio as particles decrease in size?
The surface area increases in relation to volume
166
By what factor does the surface area to volume ratio increase when the side of a cube decreases by a factor of 10?
By a factor of 10
167
Why might nanoparticles have different properties from the same materials in bulk?
Because of their high surface area to volume ratio
168
What are fullerenes?
Nanoparticles made of carbon
169
How do fullerenes behave compared to larger carbon compounds like diamond and graphite?
Very differently
170
In which two areas is the surface area to volume ratio an important feature?
Catalysis and surface chemistry
171
Why does a higher surface area to volume ratio make for better catalysts?
More surface area is available for reaction
172
What is the main industrial application of nanoparticles?
Catalysis
173
How is titanium dioxide in nanoparticle form used differently from its bulk form?
Nanoparticle form: used in sunscreens to block UV light without white marks; Bulk form: used as a white pigment in paints
174
Why are fullerenes used in medicine and drug design?
They are more easily absorbed and can deliver drugs to target areas more effectively
175
What are two other applications of fullerenes besides medicine?
Electronic circuitry and as coatings for artificial limbs and joints
176
What property makes silver nanoparticles useful in medical clothing and surgical masks?
Antibacterial properties
177
What is a primary concern about nanoparticles in relation to health?
Lack of understanding on how they may affect health, particularly long-term effects
178
Why might even a small amount of toxicity in nanoparticles be concerning?
It would be multiplied due to the high surface area to volume ratio
179
What additional factor compounds the potential risk of toxic nanoparticles?
They are not easily disposed of by the body
