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2025 summer chemistry knowledge points and questions collection > unit 1 knowledge points > Flashcards

unit 1 knowledge points Flashcards

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1
Q

What is isotopes?

A

atoms of the same element that have the same atomic number but different mass number (the number of neutrons is different)

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2
Q

What is molecular ion peak?

A

the peak with the highest m/z ratio in the mass spectrum, the M peak

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2
Q

What is relative atomic mass (Aᵣ)

A

(of an element) the weighted mean (average) mass of an atom of the element compared to 1/12 of the mass of an atom of carbon-12

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3
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7
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8
Q

What is electronegativity?

A

the ability of an atom to attract a bonding pair of electrons.

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9
Q

Electronegativity Difference and Bond Type

A

1. ΔEN ≥ 1.7: Ionic bonds (electron transfer).
2. 0.5 ≤ ΔEN < 1.7: Polar covalent bonds (unequal sharing).
3. ΔEN < 0.5: Nonpolar covalent bonds (equal sharing).
4. Exceptions exist (e.g., AgCl has covalent character despite ΔEN = 1.23 due to polarizability).

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10
Q

What is polarising power and what is polarisation?

A

1. polarising power is the ability of a positive ion to distort the electron density of a neighbouring negative ion
2. polarisation is the distortion of the electron density of a negative ion

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11
Q

Polarisation will be increase by?

A

1. high charge and small size of the cation
2. high charge and big size of the anion

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12
Q

What is ionic bonding?

A

the electrostatic attraction between oppositely charged ions

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13
Q

How does ionic radius change?

A

Decreases as the number of protons increases (as the electrons are attracted more strongly by nuleus)

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14
Q

What are the four main physical properties of ionic compounds?

A

1. high melting temperatures
2. brittleness
3. poor electrical conductivity when solid but good when molten
4. often soluble in water

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15
Q

Explain high melting temperatures of ionic compounds

A

A large amount of energy is required to overcome the electrostatic forces of attraction

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16
Q

Explain brittleness of ionic compounds

A

Ions of the same charge are side by side and repel one another

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17
Q

Explain electrical conductivity of ionic compounds

A

1. solid compounds do not conduct:
no delocalised electrons, ions are not free to move
2. molten compounds will conduct:
ions are now mobile,
and will migrate to the electrodes of opposite sign when a potential difference is applied,
the compound will undergo electrolysis if direct current used
3. solutions of compounds will conduct:
the lattice breaks down into ions when dissolves

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18
Q

Explain soluble in water of ionic compounds

A

the energy required to break apart the lattic structure and separate the ion can be supplied by the hydration of the separated ions produced

hydration:
1. oxygen end towards cations
2. hydrogen end towards anion
3. exothermic

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19
Q

How does a covalent bond form?

A

Two atomic orbitals containing a single electron from two atoms overlap with each other

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20
Q

Formation of sigma bonds?

A

An end-on overlap
(a single covalent bond between the two atoms)

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21
Q

Formation of pi bonds?

A

An sideways overlap
1. pi bond cannot form until a sigma bond has been formed
2. so pi bonds only exist between atoms joined by double or triple bonds

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22
Q

How do orbitals overlap in nitrogen molecule, ethene and HCN (hydrogen cyanide)?

A

1. nitrogen molecule: two pi bonds, one sigma bonds
2. ethene: three sigma bonds, one pi bonds
3. HCN: two sigma bonds, two pi bonds

double bond: one sigma, one pi

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23
Why the sigma bond between the two carbon atoms in ethene is stronger than pi bond?
**1.** pi bonds **break easily** (sideways overlap) **2.** pi bonds **cannot rotate** whereas sigma bonds can have free rotation
24
What is the **octet rule**?
the outer shell of each atom must have eight electrons
25
The **special examples** of the octet rule?
BeCl2 4 BCl3 6 PCl5 10 SF6 12
26
What is the **dative covalent bond**?
the bond formed when an **empty** **orbital** (of one atom) overlaps with an orbital **containing** **a** **lone** **pair** **of** **electrons** (of another atom)
27
The examples of dative covalent bond?
H3O+ NH4+ Al2Cl6 (AlCl3 in gas phase)
28
What is the **electron pair repulsion theory**?
1. the shape of a molecule or ion is caused by **repulsion** between the pairs of electrons, both **bond** pairs and **lone** pairs, that surround the **central** **atom** 2. the electron pairs arrange themselves arround the central atom so that the repulsion is at a **minimum** 3. lone pair-lone pair repulsion **>** lone pair - bond pair repulsion **>** bond pair - bond pair repulsion
29
The shapes of molecules and ions?
**1.** linear (**2** bond pairs) **2.** trigonal planar (**3** bond pairs) **3.** tetrahetral (**4** bond pairs) **e.g.** CH4 **4.** trigonal bipyramidal (**5** bond pairs) **e.g.** PCl5 **5.** octahedral (**6** bond pairs) **e.g.** SF6 **6.** trigonal pyramidal (**3** bond pairs / **1** lone pair) **e.g.** NH3 **7.** V - shaped (**2** bond pairs / **2** lone pairs) **e.g.** H2O
30
The bond angles in molecules and ions?
1. linear: 180° 2. trigonal planar: 120° 3. tetrahedral: 109.5° 4. trigonal pyramidal: 107° 5. V - shaped: 104.5° 6. trigonal bipyramidal: 90° and 120° 7. octahedral: 90° and 180°
31
What is **dipole**?
a dipole exists when two charges of equal magnitude but opposite signs are separated by a small distance
32
What is dipole moment?
the difference in magnitude between δ+ and δ- multiplied by the distance of separation between the charges
33
What is the metallic bonding?
the electrostatic force of attraction between the metal cations and delocalised electrons
34
What are the main five physical properties of metallic bonding?
1. high melting temperatures 2. good electrical conductivity 3. good thermal conductivity 4. malleability 5. ductility
35
Explain **high melting temperatures** of metallic bondings
1. need to **overcome** many of forces of attraction between the **cations** and the **delocalised** **electrons** in **giant** **lattice** structure in metals 2. so **the number of delocalised electrons** and the **charge-to-radius ratio** of the **cation** affect the melting temperature
36
Explain **electrical** **conductivity** of metallic bondings
when a potential difference is applied across the end of a metal, the delocalised electrons will be attracted to, and move towards, the positive terminal of the cell.
37
Explain the **thermal conductivity** of metallic bondings
1. **free-moving delocalised electrons** pass kinetic energy 2. **cations** are **closely packed** and pass the kinetic energy
38
Explain the **malleability** and the **ductility** of metallic bondings
1. the ability of delocalised electrons and the cations to **move** **throughout** the structure 2. so when a stress is applied, the layers of cations may **slide** **over** one another
39
What are four common giant covalent substances?
**1.** diamond **2.** graphite **3.** graphene **4.** silicon(Ⅳ) oxide
40
Why is diamond extremely hard?
**very strong C—C bonding** (each carbon atom forms four sigma bonds to four carbon atoms, in a giant 3D tetrahedral arrangement with all angles of **109.5°**)
41
Why can graphite be used as a solid lubricant?
the absorbed gases on the surface of the carbon atom, so the layers can slide easily, and that's why it is not used as a lubricant in spacecraft
42
What is the special about graphite as a good conductor of electricity?
it can only conduct electricity **parallel** to its layers, not one layer to the next
43
What is the empirical formula?
it shows the numbers of each atom in simplest whole-number ratio
44
What is the functional group?
an atom or group of atoms in a molecule that is responsible for ite chemical reactions
45
What is the homologous series?
a family of compounds with the same functional group, which differ in formula by CH₂ from the next member
46
What is the structural isomers?
compounds with the same molecular formula but different structural formulae
47
What are two improtant types of structural isomerism?
1. chain isomerism 2. position isomerism
48
What does cis- and trans- mean respectively?
They are a type of **stereoisomerism** **1.** cis-: two **identical** or **similar** **groups** are on the **same** side of a double bond or ring. **2.** trans-: two **identical** or **similar** **groups** are on **opposite** sides of a double bond or ring.
49
What is addtion reaction?
reaction in which two molecules combine to form one molecule ## Footnote unsaturated alkenes
50
What is substitution reaction?
reaction in which one atom or group is replaced by another atom or group
51
What is oxidation reaction?
reaction in which a substance **gains oxygen** or **loses hydrogen**
52
What is reduction reaction?
reaction in which a substance loses oxygen or gains hydrogen
53
What is the polymerisation reaction?
reaction in which a large number of small molecules react together to form one very large molecule
54
What is homolytic fission?
the breaking of a covalent bond where each of the bonding electrons leaves with one species, forming a free radical ## Footnote 2 radicals
55
What is heterolytic fission?
the breaking of a covalent bond so that both bonding electrons are taken by one atom ## Footnote 2 ions
56
What is free radical
a species that contains an unpaired electron
57
What is electrophile?
a species that is attracted to a region of high electron density (labelled with δ-)
58
What are three main processes used to convert crude oil into fuels?
**1.** fractional distrillation **2.** cracking **3.** reforming
59
What is fractional distrillation?
the process used to separate a liquid mixture into fractions by boiling and condensing
60
What is cracking?
the breakdown of molecules into shorter ones by heating with a catalyst (zeolite, made of Al, Si, and O)
61
What is reforming?
the conversion of straight-chain hydrocarbons into branched-chain and cyclic hydrocarbons (catalyst: Pt)
62
What is the difference between complete and incomplete combustion?
1. complete combustion **only** produces **CO₂** and **H₂O** 2. incomplete combution produces **CO** and **soot** (unburnt carbon)
63
What is catalytic converter?
1. all use small quantities of precious metals (Pt, Rh, Pd) 2. can remove CO, unburned hydrocarbons and oxides of nitrogen 3. not good at removing sulfur compounds (remove from fuels)
64
What is carbon neutral?
a considered net zero effect on the amount of carbon dioxide in the atmosphere
65
What is mechanism?
the sequence of steps in an overall reaction; each step shows what happen to the electrons involved in bond breaking or bond formation
66
The main three steps of mechanism?
**1.** **initiation** (formation of **free radicals**, bond **breaking** caused by **ultraviolet radiation**) **2.** **propagation** (**two** steps, convert the starting materials into **products**) **3.** **termination** (formation of a **molecule** from two **free** **radicals**)
67
What is hydrogenation?
a reaction involving the addtion of hydrogen
68
What is hydration?
a reaction involving the addtion of water (or steam)
69
What is diol?
a compound containing two OH (alcohol) groups
70
What do curly arrows mean?
represent the movement of electron pairs ## Footnote 1. start from a bond and move to an atom 2. start from a lone pair of electrons and move to an atom
71
What is electrophilic addition?
a reaction in which two molecules form one molecule and the attacking molecule is an **electrophile** (HBr)
72
What is carbocation?
a positive ion in which the charge is shown on a carbon atom
73
What is electron-releasing group?
a group that pushes electrons towards the atom it is joined to
74
What are monomers?
the small molecules that combine together to form a polymer
75
What is repeat unit?
the set of atoms that are joined together in large numbers to produce the polymer strcture
76
What is **incineration**?
converting polymer waste into energy by burning
77
What is **biodegradable**?
a biodegradable substance is one that can be broken down by microbes
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2025 summer chemistry knowledge points and questions collection (5 decks)

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