Question 1

Question 1Which of the following properties of the halogens

increase from F to I? I. Atomic radius II. Melting point III. Electronegativity

Answer: B (atomic radius & melting point)Reason: atomic radius increases down a group

since more electron shells are being added each time; the melting point increases since the atoms get larger & hence there are more electrons to induce more temporary dipoles which leads to stronger Van der Waals’ forces.

Question 2Which factors lead to an element having a low value

of first ionisation energy?I. Large atomic radiusII.High number of occupied energy levelsIII.High nuclear charge

Answer: A (large atomic radius & high number of occupied energy levels)

Reason: The larger the atom, the further away the outer (valence) electrons are from the nucleus; a large number of occupied energy levels gives rise to increased shielding; hence the outermost electron is more easily removed in the process: X(g) X+(g) + e-

Question 3What is the correct number of each

particle in a fluoride ion, 19F–?protons neutrons electrons

A. 9 10 8B. 9 10 9C. 9 10 10D. 9 19 10

(Total 1 mark)

Answer: CReason: the fluoride anion means that there is 1 more electron than proton to give the ion a single negative charge,; there are 10 neutrons as 10+9= 19 which is the mass number

Question 4Which properties are typical of most non-metals in

period 3 (Na to Ar)?I. They form ions by gaining one or more electrons.II. They are poor conductors of heat and electricity.III. They have high melting points.

Answer: A (II & I only)Reason: Non-metals usually form anions by gaining

electrons from metals; they are poor conductors due to only Van der Waals forces being present which cannot carry permanent charge

Question 6Rubidium is an element in the same group of the periodic

table as lithium and sodium. It is likely to be a metal which has a

A. high melting point and reacts slowly with water.B. high melting point and reacts vigorously with water.C. low melting point and reacts vigorously with water.D. low melting point and reacts slowly with water.

Answer: CReason: It is a group 1 alkali metal

Question 7When the following species are arranged in order of increasing radius, what is the correct order?

A. Cl–, Ar, K+

B. K+, Ar , Cl–

C. Cl–, K+, ArD. Ar, Cl–, K+

Answer: D (Ar<Cl->K+)Reason: Atomic radius increases down a group & from right to

left across a period. An increasing nuclear charge across a period causes the atom to contract by “pulling” the outer (valence) electrons inwards. On descending a group more shells are being added each time so the valence electrons become further away from the nucleus while at the same time they are more shielded by the extra shells.

Question 8 Which property decreases down group 7 in the periodic table? A. atomic radius B. electronegativity C. ionic radius D. melting point

Answer: B (electronegativity)Reason: On descending the group, more shells are being

added so the valence electrons are further away from the nucleus & are better shielded by the extra inner shells. This outweighs the effect of the increased nuclear charge & hence the attraction for the outer electron pair in a covalent bond is decreased.

Question 9 What is the correct sequence for the processes

occurring in a mass spectrometer?A. vaporization, ionization, acceleration, deflectionB. vaporization, acceleration, ionization, deflectionC. ionization, vaporization, acceleration, deflectionD. ionization, vaporization, deflection, acceleration

Answer: A (vaporization, ionization, acceleration, deflection)

Question 10Which of the reactions below occur as written? I. Br2 + 2I– → 2Br– + I2

II. Br2 + 2Cl– → 2Br– + Cl2

A. I onlyB. II onlyC. Both I and IID. Neither I nor II

Answer: AReason: Bromine is more reactive (stronger oxidising agent) than iodine

but less reactive than chlorine & hence will only displace iodide ions from their salts & oxidise them to iodine. Reactivity decreases down group 7 due to the electron affinity decreasing since more shells are being added, causing the valence electrons to be further away from the nucleus & better shielded.

Question 11Which general trends are correct for the oxides of the period 3 elements

(Na2O to Cl2O)? I. Acid character decreases. II. Electrical conductivity (in the molten state) decreases. III. Bonding changes from ionic to covalent.

Answer: CReason: Electricity conductivity decreases across period 3 for

the oxides since the bonding changes from ionic to covalent. Only ionic compounds can conduct electricity in the molten state; covalent compounds are uncharged species & hence are non-conductors. Acid character increases across the period.

Question 12What increases in equal steps of one from left to right in the periodic table

for the elements lithium to neon?A. the number of occupied electron energy levelsB. the number of neutrons in the most common isotopeC. the number of electrons in the atomD. the atomic mass

Answer: CReason: The atomic number (no. of protons) increases in increments of 1

across period 2; the number of electrons increases in the same manner since all atoms are neutral (the number of electrons must equal the number of protons).

Question 13Which of the physical properties below decrease with increasing atomic number for

both the alkali metals and the halogens? I. Atomic radius II. Ionization energy III. Melting point

A. I onlyB. II onlyC. III onlyD. I and III only

Answer: B (II only)Reason: The valence electrons are more easily removed

on descending a group since they are further away from the nucleus & better shielded.

Question 14Which is the correct description of polarity in F2 and HF molecules?

A. Both molecules contain a polar bond.B. Neither molecule contains a polar bond.C. Both molecules are polar.D. Only one of the molecules is polar.

Answer: D (Only one of the molecules is polar)Reason: Only HF is polar since it is composed of 2 different atoms with

very different electronegativity values.

Question 15For which element are the group number and the period number

the same?A. LiB. BeC. BD. Mg

Answer: B (Be)Reason: Beryllium is in both group 2 & period 2

Question 22i Crocetin consists of the elements carbon, hydrogen and oxygen.

Determine the empirical formula of crocetin, if 1.00 g of crocetin forms 2.68 g of carbon dioxide and 0.657 g of water when it undergoes complete combustion.

Moles C = Moles CO2 = 2.68 g/44.01 g mol-1 = 0.0609 molMoles H = 2 x moles H2O = 2 x (0.657 g/ 18.02 g mol-1) = 0.0729 molMass of C = 0.0609 mol x 12.01 g mol-1 = 0.731 gMass of H = 0.0729 mol x 1.01 g mol-1 = 0.0736 gThe remainder must be the mass of oxygen in crocetinMass of O = 1.00 - 0.731 - 0.0736 = 0.195 gMoles O = 0.195/16 = 0.0122

Carbon Hydrogen

Oxygen

Moles 0.0609 0.0729 0.0122Mole ratio

0.0609/0.0122

0.0730/0.0122

0.0122/0.0122

Emperical formula

4.99 5.98 1Empirical formula: C5H6O

Question 22iiDetermine the molecular formula of crocetin

given that 0.300 mole of crocetin has a mass of 98.5 g

Molar mass of crocetin = 98.5 g / 0.300 mol = 328 g mol-1

Total molecular mass of EF, (C5H6O) = 82.11Molar mass of MF/ Molar mass of EF =328/82.11 =

4Molecular formula: C20H24O4

Question 23iNitrogen is found in period 2 and group 5 of

the periodic table.(i) Distinguish between the terms period

and group.

Period is a horizontal row in the periodic table & a group is a vertical column

Question 23iiState the electron arrangement of nitrogen

and explain why it is found in period 2 and group 5 of the periodic table.

Electron arrangement: 2,5 Found in period 2 as electrons are in 2 energy

levels/shellsFound in group 5 as 5 outer/valence electrons

Question 24aiA sample of germanium is analysed in a mass spectrometer. The first and

last processes in mass spectrometry are vaporization and detection.State the names of the other three processes in the order in which they

occur in a mass spectrometer.

Ionization, acceleration, deflection

Question 24aiiFor each of the processes named in (a) (i),

outline how the process occurs

Ionization: sample bombarded with high energy/high-speed electrons

Acceleration: use electric field/oppositely charged plates

Deflection: magnetic field

Question 24biThe sample of germanium is found to have the

following composition:Isotope 70Ge 72Ge 74Ge 76GeRelative abundance / 22.60 25.45 36.73 15.22Define the term relative atomic mass.

Average/weighted mean of masses of all isotopes of an element;

Relative to 1 atom of 12C

Question 24biiCalculate the relative atomic mass of this

sample of germanium, giving your answer to two decimal places.

Ar = (70 x 0.226) + (72 x 0.2545) + (74 x 0.3673) + (76 x 0.1522)

= 72.89

Question 25aState the meaning of the term electronegativity.

the ability of an element/atom/nucleus to attract a bonding pair of electrons in a covalent bond

Question 25bState and explain the trend in electronegativity across

period 3 from Na to Cl.

Electronegativity increases across the period;The number of protons/nuclear charge increases

Question 28aiExplain the following statements.(a) The first ionization energy of sodium is less than

that of magnesium.

Na has a lower nuclear charge/number of protons;

electrons being removed from the same energy level/shell

Question 28aiiExplain the following statements.(ii)The first ionization energy of sodium greater

than that of potassium

The electrons in sodium are closer to the nucleus/in a lower energy level/ Na has less shielding effect

hence harder to remove the valence electrons

Question 28bExplain the following statements.The electronegativity of chlorine is higher than

that of sulfur.

Chlorine has a higher nuclear charge;Attracts the electron pair/electrons in the bond

more strongly

Question 29iExplain why the ionic radius of chlorine is less than that

of sulfur.

Chlorine has an extra proton/greater nuclear charge;

Same amount of shielding (2 inner shells);Hence outer electrons attracted more strongly

Question 29iiExplain what is meant by the term electronegativity

and explain why the electronegativity of chlorine is greater than that of bromine.

Electronegativiy is the ability of an atom to attract a bonding pair of electrons in a covalent bond

chlorine has a smaller radius/electrons are closer to the nucleus/;

hence repelled by fewer inner electrons/decreased shielding effect

Question 30A toxic gas, A, consists of 53.8% nitrogen and 46.2%

carbon by mass. At 273 K and1.01×105 Pa, 1.048 g of A occupies 462 cm3. Determine the empirical formula of A.Calculate the molar mass of the compound and determine its molecular structure.

Empirical formula of A: CN

Carbon NitrogenMoles 46.2/12.01 =

3.8553.8/14.01 =

3.85Mole ratio 1 1

Question 30 (cont’d)Moles A = volume of A/ molar volume =0.462dm3 /

22.4dm mol-3 = 0.0206Molar mass A = Mass/moles = 1.048g / 0.0206 mol =

50.8 g mol-1 Mr of empirical formula (CN) = 12.01 + 14.01 = 26.02Molar mass of A/Mr of empirical formula = 50.8/26.02

= 2.00

Hence Molecular formula of A: C2N2 Possible structure: N≡C−C≡N (Cyanogen)