OCR-A Chemistry A-Level > Definitions > Flashcards

Definitions Flashcards

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1
Q

Define first ionisation energy

A

The amount of energy needed to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions

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2
Q

Define orbital

A

The volume of space around the nucleus where an electron is most likely to be found. It can hold up to 2 electrons with opposite spin

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3
Q

Define sub-shell

A

A group of orbitals with the same energy levels within the same shell

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4
Q

Define isotopic mass

A

The mass of an isotope of an atom compared to 1/12 the mass of a carbon-12 atom

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5
Q

Define relative atomic mass

A

The weighted mean mass of an atom of an element compared to 1/12 the mass of a carbon-12 atom

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6
Q

Define shielding

A

The repulsion between electrons in the same shell which reduces the effect of nuclear charge and therefore decreases the nuclear attraction

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7
Q

Define atomic radius

A

The distance of the outermost electrons from the nucleus

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8
Q

Define nuclear charge

A

The number of protons in the nucleus of an atom

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9
Q

Define covalent bonding

A

The electrostatic force of attraction between the shared pair of electrons and the nuclei of the bonded atoms

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10
Q

Define ionic bonding

A

The electrostatic force of attraction between oppositely charged ions

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11
Q

Define metallic bonding

A

The electrostatic force of attraction between positive ions and delocalised electrons

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12
Q

Define electronegativity

A

The ability of an atom to attract the shared pairs of electrons in a covalent bond

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13
Q

Define dative covalent bond

A

When both electrons of a shared pair have been given by one of the atoms

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14
Q

Define structure in bonding

A

The study of the 3-dimensional geometric arrangement of particles in matter

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15
Q

Define bonding

A

The study of the forces that hold atoms, ions and molecules together in matter

Elements bond to get a noble gas configuration and become energetically stable

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16
Q

Define principal quantum number

A

The number given to each shell to denote their different energy levels

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17
Q

Define homologous series

A

A series of molecules with the same functional group and general formula, SUCCESSIVELY differing by one CH2 group
(they have similar chemical properties and varying physical properties)

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18
Q

Define hydrocarbon

A

A molecule that ONLY contains hydrogen and carbon atoms

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19
Q

Define saturated

A

A molecule thatONLY contains SINGLE covalent bonds

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20
Q

Define mono-unsaturated

A

A molecule that contains ONE C=C bond

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21
Q

Define unsaturated

A

A molecule that contains MANY C=C bonds

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22
Q

Define molecular formula

A

The actual number of atoms of each element in the molecule

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23
Q

Define empirical formula

A

The simplest whole-number ratio of atoms of each element in a compound

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24
Q

Define structural formula

A

Shows how the atoms are bonded within a molecule

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25
Define structural isomerism
Molecules with the **same molecular formula** but **different structural formula** _TYPES:_ - Chain - Positional group - Functional group
26
Define stereoisomerism
Molecules with the **same structural formula** but **different arrangement of atoms in space**
27
Define E/Z isomerism
A type of **stereoisomerism** that occurs due to the **restricted rotation around the C=C bond**, and **each carbon in the C=C bond is bonded to 2 different groups**
28
Define displayed formula
Shows **how the atoms are bonded in a molecule** and **ALL THE BONDS**
29
Define skeletal formula
A formula where **all the hydrogens are removed** and the **carbon skeleton** is represented by a **zigzag line**. **Functional groups are shown**.
30
Define heterolytic fission
The **breaking of a covalent bond** where **both bonding electrons** go to **ONE of the atoms in the bond**, forming a **CATION** and **ANION**.
31
Define homolytic fission
The **breaking of a covalent bond** where **one of the bonding electrons** goes to **each atom in the bond** forming **TWO FREE RADICALS**.
32
What is a free radical?
An atom with an **unpaired electron**.
33
Define electronegativity.
The **ability of an atom to attract the bonding pair in a covalent bond**.
34
What is a polar bond?
A bond with a **permanent dipole** due to **different electronegativities**.
35
What is a polar molecule?
A molecule with **an overall dipole** which **CANNOT BE SYMMETRICAL**.
36
What is a carbocation?
An **organic ion** where a **carbon atom has a positive charge**.
37
What is an electrophile?
An **electron-deficient species** which is **attracted to an electron-rich species** and **ACCEPTS an electron pair** to form a **NEW COVALENT BOND**.
38
What is a nucleophile?
An **electron-rich species** that is **attracted to an electron-deficient species** and **DONATES an electron pair** to form a **NEW COVALENT BOND**.
39
Define an addition reaction.
A reaction where **one molecule is joined to another molecule**, and forms **only one product**.
40
Define a substitution reaction.
**One species replaces another species in a molecule**, forming **2 products**.
41
Define a hydrolysis reaction.
**Water or a hydroxide ion is added to a molecule to break it into two.**
42
Define a mechanism.
A **sequence of steps drawn out** to **show the movement of electrons within a chemical reaction**.
43
Define aromatic
A **HYDROCARBON including a benzene ring**.
44
Define aliphatic
A **HYDROCARBON** with **carbon atoms joined together in chains and non-aromatic rings**.
45
Define alicyclic
A **HYDROCARBON** with **carbon atoms joined together in a non-aromatic ring**.
46
Define disproportionation
The **SIMULTANEOUS** oxidation and reduction of the **SAME SPECIES**.
47
What do oxidation states show?
The **total number of electrons** which have been **involved in bonding with another element**.
48
What is the formula for percentage error?
[ (measurement error x number of errors) / net measurement value ] x 100
49
Define a redox reaction.
When oxidation and reduction happen in a given reaction.
50
What is an oxidising agent?
Something that **causes other species to be oxidised**, by **taking electrons from the other species and becoming reduced**.
51
What is a reducing agent?
Something that **causes other species to be reduced** by **giving electrons to the other species and becoming oxidised**.
52
Define bond enthalpy.
The energy required to **break ONE MOLE** of a **SPECIFIC covalent bond** in **GASEOUS MOLECULES under standard conditions**.
53
Define average bond enthalpy.
The AVERAGE energy required to **break ONE MOLE of a SPECIFIC covalent bond** in **GASEOUS molecules**.
54
Define heat enthalpy.
A **measure of heat energy in a chemical system**. *(energy stored within the bonds)*
55
Define 🔺H.
The **CHANGE IN HEAT ENTHALPY** when a reaction occurs, in kJmol-1. *🔺H = products - reactants*
56
Define the law of conservation of energy.
Energy **CANNOT BE CREATED OR DESTROYED** but it can be **CONVERTED from one form to another.**
57
Define an exothermic reaction.
_Heat energy_ is **given out**. *🔺H is NEGATIVE because system has lost energy to surroundings and temp increases*
58
Define an endothermic reaction.
_Heat energy_ is **taken in**. *🔺H is positive, because system has more energy than surroundings which loses energy, so temp decreases*
59
Define activation energy.
The **minimum energy needed to start a reaction** by breaking existing bonds.
60
What is a catalyst?
It **increases the rate of the reaction** by **providing an alternate pathway with lower activation energy** and is **NOT USED UP** in the process. *it usually reacts to form an intermediate and is regenerated at the end*
61
62
What is a homogeneous catalyst?
A catalyst that is in the **SAME phase as the reactants**
63
What is a heterogeneous catalyst?
A catalyst in a **DIFFERENT phase to the reactants** (including immiscibility)
64
Define standard enthalpy of reaction.
The **energy change** for a **STATED reaction** in the **molar quantities shown in the STATED equation** under **STANDARD CONDITIONS** with all reactants and products in their **STANDARD STATES**. (🔺rH) *e.g. Mg (s) + 1/2 O2 (g) --> MgO (s)*
65
Define standard enthalpy of formation.
The **energy change** when **ONE MOLE of a compound** is **formed** from its **constituent elements** in their **STANDARD STATES** under **STANDARD CONDITIONS**. (🔺fH) *usually exothermic!!!*
66
Define standard enthalpy of combustion.
The **energy change** when **ONE MOLE of a substance** is **completely combusted** under **STANDARD CONDITIONS**. (🔺cH) *ALWAYS EXOTHERMIC EXOTHERMIC EXOTHERMIC*
67
Define standard enthalpy of neutralisation.
The **energy change** when **ONE MOLE of WATER** is formed by an **acid/base reaction** under **STANDARD CONDITIONS**. (🔺neutH)
68
Define calorimetry.
It involves the **practical determination of enthalpy changes**.
69
Define bond dissociation enthalpy.
The **MEAN energy needed** for **ONE MOLE** of a **given type of gaseous bond** to undergo **HOMOLYTIC FISSION**. *the breaking of one mole of bonds in gaseous molecules*
70
Define an acid.
Contains hydrogen and releases H+ ions when dissolved in water
71
What is a strong acid?
**Completely dissociates** in **aqueous solution**. (all H atoms released as H+ ions in solution)
72
What is a weak acid?
**Partially dissociates** in **aqueous solution**. (not all/small proportion of H atoms released as H+ ions in solution)
73
Define an alkali.
A base which dissolves in water and releases OH- ions into solution
74
What are the must know redox equations?
- **manganate (VII) to Mn2+** MnO4- (aq) + 5e- + 8H+ (aq) --> Mn2+ (aq) + 4H2O (l) - **dichromate (VI) to Cr3+** Cr2O7 2- (aq) + 14H+ (aq) + 6e- --> 2Cr3+ (aq) + 7H2O (l) - **iron (II) to Fe3+ iron (III)** Fe2+ (aq) --> Fe3+ (aq) + e-
75
Define empirical formula.
The simplest whole number ratio of elements in a compound.
OCR-A Chemistry A-Level
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