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A Level Chem - OCR > Topic 2 > Flashcards

Topic 2 Flashcards

1
Q

what is atomic number

A

number of protons and neutrons in the nucleus of an atom

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2
Q

what is mass number

A

total number of neutrons and protons in the nucleus of an atom

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3
Q

what is relative abundance

A

the amount of one substance compared with another

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4
Q

what is relative atomic mass

A

weighted mean mass of an atom compared with 1/12 of the mass of ana tom of Carbon-12

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5
Q

what is relative isotopic mass

A

the mass of an atom of an isotope compared with 1/12 of the mass of an atom of Carbon-12

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6
Q

what is relative formula mass

A

the mass of the formula unit of a compound with a giant structure

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7
Q

what is relative molecular mass

A

mass of a simple molecule

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8
Q

what is amount of substance

A

a quantity that uses mols as units

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9
Q

what does anhydrous mean

A

crystalline compound containing no water

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10
Q

what is Avogadro’s constant

A

number of atoms per mole of a substance
6.02 x 10^23

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11
Q

what is empirical formula and how do you calculate it

A

simplest whole number ratio of atoms of each element in a compound
1. given mass
2. divide by molar mass of each element
3. divide by smallest number
4. may need to multiply until all are whole numbers

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12
Q

what does hydrated mean

A

a crystalline that contains water

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13
Q

what is ideal gas and its equation

A

a gas which has molecules that occupy negligible space with no interactions
between them

pV = nRT

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14
Q

what is relative molecular formula

A

the average mass of one molecule of an element or compound compared to 1/12th the mass of an atom of carbon-12.

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15
Q

what is the meaning of standard solution

A

a solution of known concentration

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16
Q

rearrange pV = nRT to give the value of volume

A

v = nRT/P

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17
Q

rearrange pV = nRT to give the value of pressure

A

p - nRT/V

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18
Q

rearrange pV = nRT to give the value of moles

A

n = pV/RT

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19
Q

rearrange pV = nRT to give the value of temperature

A

T = PV/nR

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20
Q

what does each symbol in pV = nRT stand for

A

p = pressure (Pa/Pascals)
v = volume (m^3)
n = mols
R = ideal gas (8.314 J K-1 mol-1)
T = Temperature (K / Kelvin)

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21
Q

what is atom economy

A

conversion efficiency of a chemical process in terms of all atoms involved and the desired products produced.

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22
Q

what is the equation for atom economy

A

mr of desired product/ mr of all products/reactants

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23
Q

what is % yield

A

the ratio between what is experimentally obtained and what is theoretically calculated, multiplied by 100%

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24
Q

what is the equation for % yield

A

actual mass/theoretical mass x 100

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25
Q

why will actual mass always be lower than theoretical mass

A
  • some product is left in apparatus
  • some product/reactant is lost to the surroundings
  • incomplete reaction
  • reactants are not pure
26
Q

What is a dative covalent bond

A

when one of the bonding atoms donates both of the hared pair of electrons

27
Q

what is an ionic bond

A

the electrostatic forces of attraction between oppositely charged ions

28
Q

what are the properties of ionic bonding

A

high melting and boiling points - hlots of energy required to overcome the strong electrostatic forces f attraction
most are soluble in polar solvents as the ions are attracted to polar water molecules and break apart the lattice allowing water molecules to surround the ions
doesn’t conduct electricity as solid as ions are in fixed positions with no mobile charge carrier
conducts when molten/aqueous as the charge can flow

29
Q

what is covalent bonding

A

the strong electrostatic forces of attraction between a shared pair of electrons and the nuclei of bonding atoms

the overlap of atomic orbitals

30
Q

is attraction localised in a covalent bond

A

yes, it acts solely between the shared pair of electrons and the nuclei of bonding atoms

31
Q

shape of molecule with
2 bonding pairs 0 lone pairs
2 bonding pairs and 2 lone pairs

A

linear
bent/non-linear

32
Q

shape of a molecule with
3 bonding pairs and 0 lone pairs
3 bonding pairs and 1 lone pair

A

trigonal planar
triangular pyramid

33
Q

what is the shape of a molecule with
4 bonding pairs and 0 lone pairs
5 bonding pairs and 0 lone pairs

A

tetrahedral
trigonal byprimid

34
Q

what is the shape of a molecule with
6 bonding pairs and 0 lone pairs

A

octahedral

35
Q

what does a solid line mean

A

a bond in the plane of the paper

36
Q

what does a solid wedge mean

A

a bond that comes out of the plane of the paper

37
Q

what does a dotted wedge mean

A

a bond that is going into the plane of the paper

38
Q

what is electron-pair repulsion theory

A

the electron pairs that surround the central atom determine the shape of the molecule or ion
bc the electron pairs repel one another so that they are arranged as far apart as possible
the arrangement of electron pairs and minimises repulsion and thus holds the bonded atoms in a definite shape

39
Q

how much is a bond angle reduced by for each lone pair

A

2.5 degrees

40
Q

what is the bond angle for
tetrahedral
pyramidal
non-linear/bent

A

109.5
107
104.5

41
Q

what is the bind angle for
linear
trigonal planar
tetrahedral
octahedral

A

180
120
109.5
90

42
Q

what is electronegativity

A

the ability of an atom to attract a pair of electrons in a covalent bond towards itself

43
Q

what is a non polar bond

A

when the bonded electron pair is shared equally and occurs when the atoms are either the same or have the same/similar electronegativity

44
Q

what is a polar bond

A

when the electron pair is shared unequally between the bonded atoms and occurs when the bonded atoms are different or have different electronegativity values

45
Q

does a dipole in a covalent bond change

A

no, it is a permanent dipole

46
Q

what is a polar molecule and when does it occur

A

when a molecule has a net dipole as the dipoles present may reinforce one another to form a larger dipole over the whole molecule

47
Q

when do you have polar bonds and a non-polar molecule

A

when a molecule’s net dipole is cancelled out as its dipoles are acting in opposite directions

48
Q

what are intermolecular forces and what are their three categories

A

weak interactions between dipoles if different molecules
London forces
permanent dipole-dipole interactions
Hydrogen bonding

49
Q

what are london forces

A

weak intermolecular forces that exist between all molecules
act between induced dipoles of different molecules

50
Q

describe the origin of an induced dipole

A
  1. movement of electrons produces a changing dipole in a molecule
  2. at any instant, an instantaneous dipole will exist but its position is constantly shifting
  3. the instantaneous dipole induces a dipole on a neighbouring molecule
  4. the induced dipoles induces further dipoles in neighbouring molecules which then attract one another
51
Q

london forces result from interactions of electrons between molecules
the more electrons…

A
  • the larger the instantaneous and induced dipoles
  • the greater the induced dipole-dipole interactions
  • the stronger the attractive forces between molecules
52
Q

compare fluorine molecules and HCL molecules

A

fluorine non polar and only have london forces
HCl polar and have london forces and have permanent dipole dipole interactions between molecules
so bp of HCl is higher than F

53
Q

describe a simple molecular lattice

A

molecules are held in place by weak intermolecular forces
the atoms within each molecule are bonded together strongly by covalent bonds

54
Q

why do simple molecular substances have low melting and boiling points

A

weak intermolecular forces can be broken down by the energy present at low temperatures
only the weak intermolecular forces break
the covalent bonds are strong and do not break

55
Q

describe the solubility of non-polar simple molecular substances in non polar solvents

A

non polar simple molecular substances tend to be soluble in non polar solvents
- intermolecular forces form between molecules and solved and weaken intermolecular forces in the simple lattice

56
Q

describe solubility of non polar substances in polar solvents

A

little interaction between molecules in lattice and solvent molecules
intermolecular binding within polar solvent is too strong to be broken

57
Q

what does solubility of polar substances depend kn

A

strength of the dipole

58
Q

what is the electrical conductivity of simple molecular substances

A

no mobile charged particles in structure
nothing to complete an electrical circuit

59
Q

where do you find hydrogen bonds

A

between molecules containing an electronegative atom with a lone pair of electrons
O N F
or
in molecules containing a hydrogen atom attached to an electronegative atom
H-O H-N H-F

60
Q

why is ice less dense than water

A

hydrogen bonds hold water molecules apart in an open lattice structure
the water molecules are further apart than in water
solid ice is less dense than liquid water and flits

61
Q

why does water have a high mp
and bp

A

hydrogen bonds are strongmg forces - stronger than London forces
H bonds require a lot of energy to break so water has a higher than anticipated m/bp than from just London forces
when ice lattice breaks, the arrangement of H bonds is broke, when water boils, the H bonds break completely

62
Q

what are the other odd properties of water

A

high surface tensions and viscosity

A Level Chem - OCR (4 decks)

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