Atomic structure, Amount of substance, Bonding Chaps 1,2,3 Flashcards
1
Q
Define isotope.
A
Atoms with the same number of protons but a different number of neutrons.
2
Q
Define atomic number.
A
The number of protons in the nucleus of an atom.
3
Q
Define mass number
A
The sum of the protons and neutrons in the nucleus of an atom.
4
Q
Define relative atomic mass.
A
The mass of an atom relative to that of the carbon 12 isotope having the value of 12.
5
Q
Define empirical formula.
A
The simplest whole number ratio of the elements in a compound.
6
Q
Define molecular formula.
A
The exact number of atoms of each element in the formula of a compound.
7
Q
What is a functional group?
A
A functional group is an atom or group of atoms which when present in different molecules causes them to have simular chemical properties.
8
Q
When going across a period from left to right does electro-negativity increase or decrease ?
A
Increase.
9
Q
When going down a group does electro-negativity increase or decrease ?
A
Decrease.
10
Q
In larger molecules are permanent dipole forces or van der waals forces stronger ?
A
van der waals
11
Q
Define first ionisation energy.
A
The minimum amount of energy needed to remove one mole of electron from one mole of gaseous atom
12
Q
What is a structural isomer?
A
structural isomers are compounds with the same molecular formula but different structures.
13
Q
What is the general trend of first ionisation energies across period 3?
A
Increasing.
14
Q
Whats the 4 stages in a mass spectrometer?
A
1) ionisation 2) acceleration 3) deflection 4) detectionIADD
15
Q
Explain why ions formed in a mass spectrometer have a positive charge.
A
Because they have lost one (or more) electrons hence have a negative charge.
16
Q
What causes the ions to accelerate through the mass spectrometer?
A
They are attracted by a positively charged plate.
17
Q
In a mass spectrometer what forms ions into beams?
A
The ions pass through a series of holes or slits.
18
Q
In a mass spectrometer what bends the ions into a curved path?
A
A magnetic field at right angles to their direction of motion.
19
Q
What is Hess’s law
A
The enthalpy change when one mole of a compound is formed in its standard state from its elements in their standard states.
20
Q
Define standard enthalpy of combustion.
A
The energy required to remove one mole of electrons from one mole of gaseous atoms to for one mole of gaseous positive ions.
21
Q
How many electrons does the first, second and third shell hold?
A
1st - 2 electrons 2nd - 8 electrons 3rd - 18 electrons
22
Q
Define ionic bond
A
Oppositely charged ions held together in a crystal lattice by electrostatic attraction.
23
Q
Define covalent bond.
A
A shared pair of electrons one electron being supplied by each atom either side of the bond.
24
Q
Define electro-negativity.
A
The ability of an atom to attract the pair of electrons in a covalent bond to itself.
25
Define polar bond.
A covalent bond where the shared pair of electrons is displaced to one end.
26
Define bond enthalpy.
The energy required to break one mole of gaseous bonds to form gaseous atoms.
27
People who have a zinc deficiency can take hydrated zinc sulfate (ZnSO4.xH2O) as a dietary supplement.A student heated 4.38 g of hydrated zinc sulfate and obtained 2.46 g of anhydrous zinc sulfate.Use these data to calculate the value of the integer x in ZnSO4.xH2O . Show your working.
Mass of H2O = 4.38-2.46 (= 1.92 g)ZnSO4 2.46/161.5 =0.152H2O 1.92/18 =0.107(0.0152:0.152) (1:7)x=7
28
Zinc chloride can be prepared in the laboratory by the reaction between zinc oxide and hydrochloric acid.The equation for the reaction isZnO + 2HCl ZnCl2 + H2OA 0.0830 mol sample of pure zinc oxide was added to 100 cm3 of 1.20 mol dm–3hydrochloric acid.Calculate the maximum mass of anhydrous zinc chloride that could be obtained from the products of this reaction.
Moles HCl = 0.12(0)mol ZnCl2 = 0.06(0) OR 0.12 / 2mass ZnCl2 = 0.06 × 136.4= 8.18(4) (g) OR 8.2 (g)
29
Zinc chloride can also be prepared in the laboratory by the reaction between zinc and hydrogen chloride gas.Zn + 2HCl ZnCl2 + H2An impure sample of zinc powder with a mass of 5.68 g was reacted withhydrogen chloride gas until the reaction was complete. The zinc chloride produced had a mass of 10.7 g.Calculate the percentage purity of the zinc metal. Give your answer to 3 significant figures.
Moles ZnCl2 = 10.7/ 136.4= 0.0784) OR moles Zn = 0.0784Mass Zn reacting = 0.0784 × 65.4 = (5.13 g) % purity of Zn = 5.13 / 5.68 x 100 = 90.2% OR 90.3%
30
Predict the type of crystal structure in solid zinc fluoride and explain why its melting point is high.
IonicStrong (electrostatic) attraction (between ions)between oppositely charged ions / + and – ions / F– and Zn2+ ions
31
State the meaning of the term mass number of an isotope.
(Total number of) protons and neutrons (in nucleus of atom)
32
Give the symbol of the element that has an isotope with a mass number of 68 and has 38 neutrons in its nucleus.
Zn
33
State the type of bonding in lithium fluoride.Explain why a lot of energy is needed to melt a sample of solid lithium fluoride.
*Ionic*Strong or many or lots of (electrostatic) attractions (between ions)*Between + and – ions / between Li+ and F- ions / oppositely charged ions
34
Deduce why the bonding in nitrogen oxide is covalent rather than ionic.
Small electronegativity difference / difference = 0.5
35
Oxygen forms several different compounds with fluorine.Suggest the type of crystal shown by OF2
(simple) molecular
36
Write an equation to show how OF2 reacts with steam to form oxygen and hydrogen fluoride.
OF2 +H2O →O2 +2HF
37
One of these compounds of oxygen and fluorine has a relative molecular mass of 70.0 and contains 54.3% by mass of fluorine.Calculate the empirical formula and the molecular formula of this compound. Show your working.
45.7% OO 45.7 / 16 = 2.85F 54.3 / 19= 2.85(2.85:2.85) (1:1)EF = OF or FOMF (= 70.0/35) = O2F2 or F2O2
38
The element rubidium exists as the isotopes 85Rb and 87RbState the number of protons and the number of neutrons in an atom of the isotope 85Rb
37 48
39
The following equation shows the reaction of a phosphine molecule (PH3) with an H+ ion.PH3 + H+ ------>PH4+State the type of bond that is formed between the PH3 molecule and the H+ ion. Explain how this bond is formed.
Coordinate / dativePair of electrons on P(H3) donated (to H+)
40
Graphene is a new material made from carbon atoms. It is the thinnest and strongest material known. Graphene has a very high melting point and is an excellent conductor of electricity.Suggest why graphene is an excellent conductor of electricity.
Delocalised electrons / free electrons Able to move / flow (through the crystal)
41
Graphene is a macromolecular or giant covalent structure. In terms of its structure and bonding, why graphene has a high melting point.
Covalent bondsMany /strong / hard to break / need a lot of energy to break
42
Titanium is also a strong material that has a high melting point. It has a structure similar to that of magnesium.State the type of crystal structure shown by titanium.
(Giant) metallic / metal (lattice)
43
Explain, in terms of its structure and bonding, why titanium has a high melting point.
Nucleus / protons / positive ions and delocalised electrons (are attracted)Strong attraction
44
Titanium can be hammered into objects with different shapes that have similar strengths.Suggest why titanium can be hammered into different shapes.
Layers of atoms/ions slide (over one another)
45
Suggest why these objects with different shapes have similar strengths.
(Strong) (metallic) bonding re-formed / same (metallic) bonding / retains same (crystal) structure / same bond strength / same attraction between protons and delocalised electrons as before being hammered or words to that effect
46
Magnesium oxide (MgO) has a melting point of 3125 K.Predict the type of crystal structure in magnesium oxide and suggest why its melting point is high.
*(giant) Ionic*Between + and – ions / oppositely charged ions or Mg2+ and O2-*Strong attraction
47
Fluorine forms compounds with many other elements.Fluorine reacts with bromine to form liquid bromine trifluoride (BrF3).State the type of bond between Br and F in BrF3 and state how this bond is formed.
CovalentShared pair(s) of electrons / one electron from Br and one electron from F
48
BrF4– ions are also formed when potassium fluoride dissolves in liquid BrF3 to form KBrF4Explain, in terms of bonding, why KBrF4 has a high melting point.
*ionic or (forces of) attraction between ions / bonds between ions*Strong (electrostatic) attraction / strong bonds / lots of energy needed to break bonds*Between K+ and BrF4- ions/oppositely charged ions / + and - ions
49
Fluorine reacts with hydrogen to form hydrogen fluoride (HF).State the strongest type of intermolecular force between hydrogen fluoride molecules.
Hydrogen bonds
50
The boiling points of fluorine and hydrogen fluoride are –188 oC and 19.5 oC respectively. Explain, in terms of bonding, why the boiling point of fluorine is very low.
vdw / van der Waals forces between moleculesIMF are weak / need little energy to break IMF / easy to overcome IMF
51
When lead(II) nitrate is heated it decomposes to form lead(II) oxide, nitrogen dioxide and oxygen.Balance the following equation that shows this thermal decomposition. ........Pb(NO3)2(s) → ....... PbO(s) + .......NO2(g) + .......O2(g)
2Pb(NO3)2(s) → 2 PbO(s) + 4NO2(g) + (1)O2(g)
52
Suggest one reason why the yield of nitrogen dioxide formed during this reaction is often less than expected.
*Decomposition not complete*side reactions *by-products *some (NO2) escapes *not all reacts*impure Pb(NO3)2
53
Suggest one reason why it is difficult to obtain a pure sample of nitrogen dioxide from this reaction.
Hard to separate O2 from NO2 / hard to separate the 2 gases
54
There are several types of crystal structure and bonding shown by elements and compounds.Name the type of bonding in the element sodium.
Metallic
55
Sodium reacts with chlorine to form sodium chloride. Name the type of bonding in sodium chloride.
Ionic
56
Explain why the melting point of sodium chloride is high.
Strong (electrostatic) attractionBetween oppositely charged ions / particles
57
Suggest why the melting point of sodium iodide is lower than the melting point of sodium bromide.
Iodide / I– bigger (ion) (so less attraction to the Na+ ion)
58
Water can be found as ice, water and steam-why ice is less dense than water.
Water or H2O or molecules (in ice) are held further apart (than in liquid water) with (more) space/gaps/holes in structure
59
State the strongest type of intermolecular force holding the water molecules together in the ice crystal.
Hydrogen bonding
60
State the strongest type of intermolecular force in methane.
Give one reason why the melting point of ice is higher than the melting point of methane.
61
Give one reason why the melting point of ice is higher than the melting point of methane.
Hydrogen bonding is stronger than van der Waals forces
62
Water can also form the hydroxide ion.State the number of lone pairs of electrons in the hydroxide ion.
3
63
State the type of structure shown by a crystal of silicon. Explain why the melting point of silicon is very high.
Macromolecular/giant covalent/ giant molecular / giant atomicMany/strong covalent bondsBonds must be broken/overcome
64
State the type of structure shown by crystals of sulfur and phosphorus.Explain why the melting point of sulfur is higher than the melting point of phosphorus.
(Simple) molecularS bigger molecule (than P) or S8 and P4 referencesSo more/ stronger van der Waals‟ forces (to be broken or overcome)
65
Explain why the melting point of aluminium is higher than the melting point of sodium.
Bigger charge (3+ compared to 1+)More free /delocalised electrons (in Al)/bigger sea of electrons in AlStronger metallic bonding/ stronger (electrostatic) attraction between the (+) ions or nuclei and the (delocalised) electrons ( or implied)
66
Fluorine forms many compounds that contain covalent bonds. State the meaning of the term covalent bond.
shared pair of electrons
67
Write an equation to show the formation of one molecule of CIF3 from chlorine and fluorine molecules.
1/2 Cl2 + 3/2 F2 -> ClF 3
68
Suggest the strongest type of intermolecular force between CCI2F2 molecules.
Dipole – dipole
69
Give one reason why the oxide NO is a pollutant gas.
Toxic/ poisonous/ forms an acidic gas / 1 forms NO2 which is acidic/ respiratory irritant/ forms HNO3when NO reacts with water and oxygen/triggers asthma attacks/ greenhouse gas/photochemical smog/ contributes to global warming /formation of acid rain
70
The oxide NO reacts with oxygen to form nitrogen dioxide. Write an equation for this reaction.
2NO+O2----->2NO2
71
Explain how NO is produced in the engine of a motor vehicle.
Nitrogen / N2 and oxygen / O2 combine/react 1spark / high temperature / 2500-4000  C
72
Write an equation to show how NO is removed from the exhaust gases in motor vehicles using a catalytic converter.
2NO + 2CO----->N2 + 2CO2
73
Iodine and graphite are both solids. When iodine is heated gently a purple vapour is seen. Graphite will not melt until the temperature reaches 4000 K. Graphite conducts electricity but iodine is a very poor conductor of electricity.State the type of crystal structure for each of iodine and graphite.
Iodine – molecular Graphite- macromolecular/giant covalent/giant atomic
74
Describe the structure of and bonding in graphite and explain why the melting point of graphite is very high.
*Layers of (C atoms)*Connected by covalent bonds within each layer*Van der Waals forces/ IMF between layers/ weak forces between layers*Many/strong covalent bonds need to be broken
75
Explain why iodine vaporises when heated gently.
Van der Waals forces are weak or easily broken Van der Waals between molecules (or implied)
76
State why iodine is a very poor conductor of electricity---->
Does not have delocalised/free electrons
77
Define the term mass number of an atom.The mass number of an isotope of nitrogen is 15. Deduce the number of each of thefundamental particles in an atom of 15N
Mass number = number of protons + neutrons (in the nucleus/atom)7 protons and 7 electrons 8 neutrons
78
State the strongest type of intermolecular force in water and in hydrogen sulfide (H2S)
Hydrogen/H bonds van der Waals/vdw/ dipole-dipole
79
Explain why the boiling point of water is much higher than the boiling point of hydrogen sulfide.
Hydrogen bonds/IMF (in water) stronger OR IMF / VDW / dipole-dipole forces (in H2S) are weaker
80
Explain why the boiling points increase from H2S to H2Te
Atoms/molecules get larger/more shells/more electrons/ more surface areatherefore increased Van der Waals/IMF forces
81
When H+ ions react with H2O molecules, H3O+ ions are formed.Name the type of bond formed when H+ ions react with H2O molecules. Explain how this type of bond is formed in the H3O+ ion.
Dative (covalent)/ coordinate(Lone) pair/both electrons/two electrons on O(H2) donated (to H+) OR pair/both electrons come from O(H2)
82
Sodium sulfide (Na2S) has a melting point of 1223 K.Predict the type of bonding in sodium sulfide and explain why its melting point is high.
ionic oppositely charged ions /+ and – ions or particles ions attract strongly OR strong/many (ionic) bonds must be broken
83
Complete the electron arrangement of the selenium (Se) atom.1s2 ..............
1s22s22p63s23p64s23d104p4
84
State the block in the Periodic Table to which selenium belongs. Explain your answer.
p blockHighest energy / outermost e-/e-s in ‘p’ orbital/sub-level
85
State what is meant by the term mass number of an atom.
Sum of amount of protons and neutrons
86
Deduce the symbol, including the mass number, of an atom that has four fewer protons and four fewer neutrons than an atom of 76Se
68Zn
87
Explain how atoms are ionised in a mass spectrometer.
High energy e- / high speed e- / e- from electron gunKnock e- off (atom)
88
State how the ions are detected when they collide with the detector in a mass spectrometer
(Ions) generate/produce a current (on collision at the detector)
89
Balance the following equation:Al2Se3 + ...... H2O → ...... Al(OH)3 + ...… H2SeDescribe how the covalent bonds are formed in an H2Se molecule.
Al2Se3 + 6H2O → 2Al(OH)3 + 3H2Secovalent bond is a shared e- pair; Se supplies one e- and H supplies one/the other e-;
90
An empirical formula can be used to deduce the molecular formula of a compound. State what is meant by the term molecular formula.
(Actual) number of atoms of each element in a molecule/compound
91
State the information, other than the empirical formula, that you would need to deduce the molecular formula of a compound.
The Mr / relative molecular/formula mass
92
The melting points of the Period 3 elements silicon, sulphur and chlorine are 1683 K, 386 K and 172 K, respectively. Explain, in terms of the structure and bonding present, why the melting point of silicon is very high, and why the melting point of chlorine is lower than that of sulphur (7)
Macromolecular/giant atomic/giant covalent structure;Covalent bonds must be broken/overcome;Much energy to break bonds/bonds strong/many bonds to break; S and Cl both (simple) molecular / S8 & Cl2 / separate refs to molecules;vdW forces increase with number of e-/size/Mr etc; Van der Waals’ forces present in both (or implied);e-/size/Mr is smaller for Cl molecules;
93
Use your knowledge of structure and bonding to deduce why sodium metal can be beaten into shape when hit with a hammer but solid sodium chloride breaks into small pieces.
Correct bonding in both structures – accept correct descriptionsIn Na, atoms/ions/layers/particles slide/move when struck (but still 1 metallic bonding);Idea that, in NaCl, ions of same charge repel each other;
94
A sample from a meteorite was found to contain the isotopes 54Fe,56Fe and 57Fe.a- The relative abundances of these isotopes can be determined using a mass spectrometer. In the mass spectrometer, the sample is first vaporized and then ionised.(i) State what is meant by the term isotopes.(ii) Explain how, in a mass spectrometer, ions are detected and how their abundance is measured
(i) Isotopes of the same element have the same number of protons but different number of neutrons.Par example: 14C & 12C are both isotopes of the Carbon, both of them have 6 protons. When counting the neutrons 14C has 8 neutrons & 12C has only 6 neutrons.(ii)-detected by: positive ions collide with /are deflected to / are collected at the detector-causing current to flow / detected electrically-abundance measured: current depends on number of ions hitting detector
95
A sample from a meteorite was found to contain the isotopes 54Fe,56Fe and 57Fe.a- The relative abundances of these isotopes can be determined using a mass spectrometer. In the mass spectrometer, the sample is first vaporized and then ionised.(i) State what is meant by the term isotopes.(ii) Explain how, in a mass spectrometer, ions are detected and how their abundance is measured.b-(i) Define the term relative atomic mass of an element.(ii) The relative abundances of the isotopes in this sample of iron were found to be as follows.m/z 54 56 57Relative Abundance (%) 5.8 91.6 2.6Use the date above to calculate the relative atomic mass of iron in this sample. Give your answer to one decimal place. (i)Give the electron arrangement of an Fe2+ ion.(ii)State why iron is placed in the d block of the periodic table.(iii)State the difference, if any, in the chemical properties of isotopes of the same element. Explain your answer
The relative atomic mass of an element is the weighted average of the masses of its isotopes on a scale on which a carbon-12 atom has a mass of exactly 12 units. 55.9i- Iron has 26 electrons.The Ion Fe2+ means that the Iron has lost 2 electrons. Therefore, in total Fe2+ has 24 electrons.A shorthand way of writing electronic structures for Fe2+ which has 24 electrons is as follows:1s2 2s2 2p6 3s2 3p6 3d6 ii- Iron is placed in the d block of the periodic table just because its highest energy electrons are in 3d.iii- There are no difference in chemical properties of isotopes of the same element because these properties are controlled by the electrons. The change in the nucleus does not change chemical or physical properties.
96
(a)- Give the relative charge and relative mass of an electron.(b)- Isotopes of Chromium include 54Cr and 52Cr (i) - Give the number of protons present in an atom of 54Cr. (ii) - Deduce the number of neutrons present in an atom of 52Cr. (iii)- Apart from the relative mass of each isotope, what else would need to be known for the relative atomic mass of chromium to be calculated?(c)- In order to obtain a mass spectrum of a gaseous sample of chromium, the sample must be first ionised. (i) - Give two reasons why it is necessary to ionise the chromium atoms in the sample. (ii) - State what is adjusted so that each isotopes of chromium can be detected in turn. (iii)- Explain how the adjustment given in part (c)(ii) enables the isotopes of chromium to be separated
a- The relative charge of an electron is -1 and its relative mass is 1/1840 ( very nearly 0)b-iIsotopes are atoms with the same number of protons but different numbers of neutrons. Atoms of different isotopes of the same element vary in mass number because of the different number of neutrons in their nuclei alas they have the same Atomic Number Z. Looking at the periodic table we can see that the Atomic Number of Chromium is 24 therefore the number of protons present in an atom of 54Cr is 24b-ii52CrNumber of protons = 24Number of electrons = 24Number of Neutrons: 52 - 24 = 28b-iiiTo calculate the relative mass of Chromium we need to know the relative abundance of the isotopes in addition to the relative mass of each of the Chromium isotopes. c-iThe atom Chromium is ionised by knocking one or more electrons off to give a positive ion. This happens when a beam of high-energy electrons coming out from electrons gun knock out electrons from atoms or molecules of the sample, which is Crhere, so that they form positive ions.Why Ionisation is necessary? Ions are formed in order to be, 1-Accelerated by an electric field.2-Deflected by a magnet/Magnetic field.3-Detected by the current formed at the detector.c-iiIn a mass spectrometer in order to direct ions with different m/z values onto the detector the strength of the magnetic field must be adjusted. c-iiiThe angle of deflection of the ion is proportional to the charge and inverted to its mass.This means the ions with small value of m/z will be easily deflected and directed to the detector when the strength of the magnetic field is low. When we increase the strength of the magnetic field, the ion with higher value of m/z will be directed on the detector.Ions strike the detector, accept electrons, lose their charge and create a current which is proportional to the abundance of each ion.From the strength of the magnetic field at which a particular ion hits the detector, a computer works out the value of the mass to the charge m/z, of the original ion. A read-out called a mass spectrum is produced.
