Transition Elements · Practice

All questions with answers · Transition Elements

1. At normal air pressure, pure water boils at 100 °C and ethanol (alcohol) boils at 78 °C. What does this tell you?

   • A. The forces between water particles are stronger than those between ethanol particles.
   • D. Nothing, because the boiling point depends on how much liquid you heat.
   • C. Water particles are heavier, so water needs more heating to boil.
   • B. The forces between ethanol particles are stronger, because ethanol boils first.

   Answer: The forces between water particles are stronger than those between ethanol particles.

   To boil, particles must break free from each other. Stronger forces need more heating, so the boiling point is higher. Water boils at 100 °C and ethanol at 78 °C. So water particles hold each other more strongly. Mass is not the reason: an ethanol particle is heavier than a water particle. The amount of liquid does not change the boiling point either. Key words: stronger forces between particles, higher boiling point.

2. Substance	Melting point (°C)	Boiling point (°C)
   P	-20	80
   Q	30	290
   R	120	400

   The table gives the melting and boiling points of three substances. Which one is a liquid at 100 °C?

   • B. Q
   • C. R
   • A. P

   Answer: Q

   A substance is a liquid between its melting point and its boiling point. Below the melting point it is a solid. Above the boiling point it is a gas. P: 100 °C is above its boiling point (80 °C), so P is a gas. Q: 100 °C lies between 30 °C and 290 °C, so Q is a liquid. R: 100 °C is below its melting point (120 °C), so R is still solid. Compare the temperature with both values, not just one.

3. In which substance are the atoms joined by covalent bonds?

   • B. NH3$\mathrm{NH}{}_3$
   • C. Na2O$\mathrm{Na}{}_2\mathrm{O}$
   • A. CaCl2$\mathrm{CaCl}{}_2$

   Answer: NH3$\mathrm{NH}{}_3$

   Look at the kinds of atoms. A metal and a non-metal: the metal gives electrons, ions form, and the bond is ionic. Two non-metals: the atoms share pairs of electrons, and the bond is covalent. CaCl2$\mathrm{CaCl}{}_2$ and Na2O$\mathrm{Na}{}_2\mathrm{O}$ each contain a metal, so they are ionic. NH3$\mathrm{NH}{}_3$ has only non-metals (N and H), so its bonds are covalent.

4. Potassium (K) has 1 outer electron. Sulphur (S) has 6 outer electrons. Which describes the bonding in potassium sulphide, K2S$\mathrm{K}{}_2\mathrm{S}$?

   • D. No electrons move, because K and S are only mixed together.
   • A. Each K atom gives one electron to S, and the ions formed attract.
   • B. The K and S atoms share pairs of electrons with each other.
   • C. The S atom gives two electrons, one to each K atom.

   Answer: Each K atom gives one electron to S, and the ions formed attract.

   Potassium is a metal with 1 outer electron. Sulphur is a non-metal that needs 2 more electrons. So two K atoms each give one electron to one S atom. K+$\mathrm{K}{}^{+}$ and S²⁻$\mathrm{S}{}^{2-}$ ions form. Opposite charges attract: this is an ionic bond. That is why the formula has two K for one S.

5. What holds the atoms together in a piece of silver metal?

   • B. Pairs of electrons shared between two neighboring silver atoms
   • C. Positive and negative silver ions attracting each other
   • A. Positive silver ions attracted to a sea of free valence electrons

   Answer: Positive silver ions attracted to a sea of free valence electrons

   In a metal, each atom releases its valence (outer) electrons. The atoms become positive ions in a regular crystal lattice. The free electrons move among the ions and hold them together. This is the metallic bond. It is not covalent: no fixed pairs are shared. It is not ionic: there are no negative ions.

6. Lithium (Li) gives 1 valence electron per atom to its metallic bond. Beryllium (Be), the next element, gives 2. Which prediction about their melting points is correct?

   • C. They melt at about the same temperature, because they are neighbors.
   • D. Be melts higher, because its atoms share fixed pairs of electrons.
   • A. Be melts higher, because its extra free electron makes its metallic bond stronger.
   • B. Be melts higher, because its atoms are heavier than lithium atoms.

   Answer: Be melts higher, because its extra free electron makes its metallic bond stronger.

   In the metallic bond, positive ions are held by a sea of free valence electrons. Lithium gives 1 electron per atom; beryllium gives 2. For these two neighbors, more free electrons per atom make a stronger metallic bond. (Other factors also matter, so this is not a rule for every pair of metals.) A stronger bond needs more heat to break, so Be melts higher. Real values: Li melts at 181 °C, Be at 1287 °C. Mass is not the reason: Be is only slightly heavier than Li.

7. A metal bar has a density of 7.9 g/cm³. You cut it into two equal halves. What is the density of one half?

   • A. 3.95 g/cm³
   • C. 15.8 g/cm³
   • B. 7.9 g/cm³

   Answer: 7.9 g/cm³

   Density = mass ÷ volume. Cutting the bar in half halves the mass and halves the volume. The ratio stays the same: 7.9 g/cm³. Density belongs to the substance, not to the size of the piece. Pieces of the same pure metal have the same density.

8. A metal cube has a mass of 33.6 g and a volume of 4 cm³. Calculate its density in g/cm³.

   Answer: 8.4 ± 0.05 g/cm³

   Density = mass ÷ volume = 33.6 g ÷ 4 cm³ = 8.4 g/cm³. Common mistake 1: multiplying, 33.6 × 4 = 134.4. Density is mass per unit volume, so divide. Common mistake 2: volume ÷ mass, 4 ÷ 33.6 = 0.12. The mass goes on top.

9. Element	Atomic number	Atomic mass	Atomic radius
   Sc$\mathrm{Sc}$	21	45	1.44
   Ti$\mathrm{Ti}$	22	47.9	1.32
   V$\mathrm{V}$	23	51	1.22
   Cr$\mathrm{Cr}$	24	52	1.17
   Mn$\mathrm{Mn}$	25	54.9	1.17
   Fe$\mathrm{Fe}$	26	55.9	1.16
   Co$\mathrm{Co}$	27	58.9	1.16
   Ni$\mathrm{Ni}$	28	58.7	1.15
   Cu$\mathrm{Cu}$	29	63.5	1.17

   Use the table. Which pair of neighboring elements does not follow the general trend of atomic mass?

   • B. Fe and Co
   • C. Co and Ni
   • D. Ni and Cu
   • A. Cr and Mn

   Answer: Co and Ni

   The general trend: atomic mass increases gradually with increasing atomic number. Scan the atomic mass column from Sc to Cu. Every step rises except one: Co 58.9 to Ni 58.7. So nickel is abnormal. The book's reason: nickel has five stable isotopes with average mass 58.7 u. Equal values for Cr and Mn are in the radius column. The big rise from Ni to Cu still follows the trend.

10. Give reasons: The decrease in atomic radius across the first transition series is small.

    Answer: Key points: two opposite factors. (1) The effective nuclear charge increases, so the nuclear attraction to electrons increases; this decreases the atomic radius. (2) The number of electrons in the 3d sublevel increases, so the repulsion between them increases; this increases the atomic radius. (3) The two factors oppose each other, so the atomic radius stays relatively constant (nearly constant from Cr to Cu).

    A full answer names both factors and their opposite effects. Factor 1: the effective nuclear charge increases, so the nuclear attraction to electrons increases. This tends to decrease the radius. Factor 2: more electrons enter the 3d sublevel, so the repulsion between them increases. This tends to increase the radius. The two factors oppose each other, so the radius changes little. Most likely wrong answer: only the nuclear charge. Alone, it would make the radius fall sharply, as across period 3.

11. Choose the correct answer: The metallic property appears clearly in the first transition elements, as all of them are ...

    • B. solids with limited chemical activity, like copper
    • D. solids that go rusty when exposed to moist air
    • A. solids with metallic luster that conduct heat and electricity well
    • C. active metals that replace the hydrogen of water strongly

    Answer: solids with metallic luster that conduct heat and electricity well

    Book point 3a: all of them are solids, with metallic luster and good conductivity of heat and electricity. These properties are shared by the whole series. Chemical activity is different: it varies (point 3d). Copper has limited activity, iron is moderate, and scandium is highly active. So options about activity describe only one member each.

12. Give reasons: The first transition elements have high melting and boiling points.

    Answer: Key points: (1) They have a strong metallic bond. (2) This bond is formed by the sharing of both 4s and 3d electrons.

    To melt or boil a metal, the metallic bond must be overcome. In these elements, both 4s and 3d electrons share in forming the metallic bond. Here, the many electrons sharing in the bond make it strong, so a lot of heat is needed. Key words: strong metallic bond, sharing of both 4s and 3d electrons. Most likely wrong answer: 'their atoms are heavy'. Mass does not decide melting points. Another wrong answer: 'only 4s electrons form the bond'. Then their metallic bond would be weak, more like calcium's (Ca melts at 842 °C).

13. Give reasons: The density of the first transition elements increases with increasing atomic number.

    Answer: Key points: (1) The atomic mass increases with atomic number. (2) The atomic size (radius) stays relatively constant. (3) So more mass is packed into nearly the same volume, and the density increases.

    Density = mass ÷ volume. Across the series, the atomic mass increases. But the atomic size stays relatively constant, because of the two opposite factors. So each atom adds more mass in nearly the same volume. The density therefore increases. Key words: atomic mass increases, atomic size relatively constant. Most likely wrong answer: 'the atoms get much smaller'. From Cr to Cu, the radius hardly changes, yet density still rises.

14. Give reasons: Nickel (₂₈${}_{28}$Ni) is abnormal in the gradual increase of atomic mass across the first transition series.

    Answer: Key points: (1) Atomic mass increases gradually with increasing atomic number. (2) Nickel's atomic mass (58.7 u) is less than cobalt's (58.9 u), although nickel comes after cobalt. (3) Nickel has five stable isotopes. (4) Its atomic mass, 58.7 u, is the average mass of these isotopes.

    Atomic mass usually rises with atomic number. Nickel (Z = 28) comes after cobalt (Z = 27), but its atomic mass is smaller. The reason is in its isotopes. Nickel has five stable isotopes, and 58.7 u is their average mass. Most nickel atoms are the light isotope nickel-58, so the average stays low. Key words: five stable isotopes, average mass 58.7 u. Most likely wrong answer: 'nickel has fewer protons'. No: nickel has 28 protons, cobalt 27. Another wrong answer: 'the value is a misprint'. It is a real average.

15. Element	Atomic radius
    Sc	1.44
    Ti	1.32
    V	1.22
    Cr	1.17
    Mn	1.17
    Fe	1.16
    Co	1.16
    Ni	1.15
    Cu	1.17

    The graph shows the atomic radius from Sc to Cu. In which part does the increasing effective nuclear charge clearly win over the repulsion between 3d electrons?

    • A. From Sc to Cr
    • D. Nowhere in the series
    • B. From Cr to Ni
    • C. From Ni to Cu

    Answer: From Sc to Cr

    When the effective nuclear charge wins, the radius clearly decreases. From Sc (1.44) to Cr (1.17), the radius falls clearly. So the nuclear attraction wins there. From Cr to Cu, the values stay between 1.15 and 1.17. There the 3d repulsion balances the attraction, so the radius is nearly constant. A larger nuclear charge alone does not mean a smaller atom. The repulsion must also be counted.

16. Consider the following statements: (I) Iron has moderate activity: it goes rusty if exposed to air. (II) Copper replaces the hydrogen of water strongly. (III) Scandium is a good conductor of heat and electricity. Which of these statements is/are correct?

    • C. (I) and (III)
    • A. (I) only
    • D. (II) and (III)
    • B. (I) and (II)

    Answer: (I) and (III)

    (I) is correct: the book calls iron moderate, since it goes rusty if exposed to air. (II) is wrong: copper has limited chemical activity. Scandium is the one that replaces the hydrogen of water strongly. (III) is correct: all of them have metallic luster and good conductivity of heat and electricity. Activity varies from member to member, but conductivity is shared.

17. Element	Atomic mass	Melting point (°C)
    Sc$\mathrm{Sc}$	45	1397
    Ti$\mathrm{Ti}$	47.9	1680
    V$\mathrm{V}$	51	1710
    Cr$\mathrm{Cr}$	52	1890
    Mn$\mathrm{Mn}$	54.9	1247
    Fe$\mathrm{Fe}$	55.9	1538
    Co$\mathrm{Co}$	58.9	1490
    Ni$\mathrm{Ni}$	58.7	1492
    Cu$\mathrm{Cu}$	63.5	1083

    Use the table. Compare vanadium and iron. Which conclusion is correct?

    • D. Melting point falls steadily with increasing atomic number.
    • B. Heavier atoms melt higher, so iron's value must be a misprint.
    • C. Iron's 3d electrons do not share in its metallic bond.
    • A. Atomic mass does not decide the melting point; bond strength does.

    Answer: Atomic mass does not decide the melting point; bond strength does.

    Vanadium: atomic mass 51, melting point 1710 °C. Iron: atomic mass 55.9, melting point 1538 °C. Iron is heavier but melts lower. So atomic mass does not decide the melting point. The strength of the metallic bond decides it. The book: both 4s and 3d electrons share in this strong bond. The values do not change steadily: they rise from Sc to Cr, then vary.

18. Element	Atomic mass	Atomic radius
    Ti$\mathrm{Ti}$	47.9	1.32
    Mn$\mathrm{Mn}$	54.9	1.17
    Fe$\mathrm{Fe}$	55.9	1.16
    Co$\mathrm{Co}$	58.9	1.16

    The table gives the atomic mass and atomic radius of four elements. Without the density column, which element has the highest density?

    • D. Mn, Fe and Co equally
    • C. Co
    • A. Ti
    • B. Fe

    Answer: Co

    Density = mass ÷ volume. Atoms of nearly equal radius take nearly the same volume. Mn, Fe and Co have nearly equal radii (1.16 to 1.17). Among them, Co has the largest atomic mass, 58.9. So Co packs the most mass into about the same volume. Ti has larger atoms (1.32) and a smaller mass, so it is the least dense. Book values: Ti 4.42, Mn 7.21, Fe 7.87, Co 8.70 g/cm³.

19. In a laboratory, a sample of nickel is made only of nickel-60 atoms. Cobalt's atomic mass is 58.9. What is true about the atomic mass of this nickel sample?

    • D. It cannot be found without the number of protons
    • B. It is 58.7, as nickel always has this mass
    • C. It is less than cobalt's, as nickel is abnormal
    • A. It is about 60, greater than cobalt's

    Answer: It is about 60, greater than cobalt's

    Natural nickel is a mix of five stable isotopes. Its atomic mass, 58.7 u, is their average. Most natural nickel atoms are the light nickel-58, so the average is below cobalt's 58.9. This sample has only nickel-60 atoms. So its average mass is about 60, greater than cobalt's. Nickel's abnormality comes from its isotope mix, not from its protons.

20. Consider the following statements about the atomic radius in the first transition series: (I) The effective nuclear charge increases, which tends to decrease the atomic radius. (II) The repulsion between 3d electrons increases with their number, which tends to decrease the atomic radius. (III) The two factors oppose each other, so the atomic radius is nearly constant from Cr to Cu. Which of these statements is/are correct?

    • C. (I) and (III)
    • B. (I) and (II)
    • A. (I) only
    • D. (II) and (III)

    Answer: (I) and (III)

    (I) is correct. The effective nuclear charge increases, so the nuclear attraction to electrons increases. This decreases the radius. (II) is wrong. More 3d electrons repel each other more, which increases the radius, not decreases it. (III) is correct. The two opposite factors balance, so the radius is nearly constant from Cr to Cu.

21. Element X is in the first transition series. Its atom has the electronic configuration [Ar] 4s²\,3d¹$4s^{2}3d^1$. Which describes the chemical activity of X?

    • D. No activity, since its 3d sublevel is almost empty
    • C. High activity: it replaces the hydrogen of water strongly
    • A. Limited activity, like copper
    • B. Moderate activity: it goes rusty in air, like iron

    Answer: High activity: it replaces the hydrogen of water strongly

    Step 1: name X. [Ar] 4s²\,3d¹$4s^{2}3d^1$ has one 3d electron, so X is the first element, scandium (Z = 21). Step 2: recall its activity. The book says scandium is highly active: it replaces the hydrogen of water strongly. Activity varies across the series: copper limited, iron moderate, scandium highly active.

22. Vanadium (₂₃${}_{23}$V) has the configuration [Ar] 4s²\,3d³$4s^{2}3d^3$. Using the book's reason for high melting points, how many electrons of each vanadium atom can share in the metallic bond?

    • A. 2
    • D. 23
    • B. 3
    • C. 5

    Answer: 5

    The book: the strong metallic bond forms by the sharing of both 4s and 3d electrons. Vanadium has 2 electrons in 4s and 3 in 3d. So 2 + 3 = 5 electrons per atom can share in the bond. The inner [Ar] electrons do not take part. Calcium, [Ar] 4s²$4s^2$, has only its two 4s electrons. That is why vanadium's metallic bond is much stronger.

23. Element	Atomic mass	Atomic radius	Density (g/cm³)
    Sc$\mathrm{Sc}$	45	1.44	3.10
    Ti$\mathrm{Ti}$	47.9	1.32	4.42

    From Sc to Ti, the atomic mass rises by only about 6%, but the density rises by about 43%. Use the table. Which statement explains the large rise?

    • D. Titanium melts higher, so its atoms pack more mass.
    • A. The mass rises and the radius falls; both raise the density.
    • B. The rise in atomic mass alone explains the rise.
    • C. Titanium atoms are larger, so each holds more mass.

    Answer: The mass rises and the radius falls; both raise the density.

    Density = mass ÷ volume. From Sc to Ti, the atomic mass rises from 45 to 47.9. The atomic radius also falls, from 1.44 to 1.32. So each atom has more mass in a smaller volume. Both changes raise the density, from 3.10 to 4.42 g/cm³. From Cr to Cu, the radius is nearly constant. There, the rising atomic mass is the main reason.

24. Manganese (₂₅${}_{25}$Mn) and copper (₂₉${}_{29}$Cu) have the same atomic radius in the book's table (1.17), although copper has four more protons. Which statement explains this?

    • C. Copper has only one 4s electron, which stops its atom shrinking.
    • B. More 3d repulsion in Cu balances its greater nuclear attraction.
    • A. The nuclear attraction stays the same from Mn to Cu.
    • D. Copper atoms are heavier, so they take up more space.

    Answer: More 3d repulsion in Cu balances its greater nuclear attraction.

    From Mn to Cu, the effective nuclear charge increases, so the nuclear attraction increases. Alone, this would shrink the atom. But the 3d electrons also increase, from 3d⁵${}^5$ in Mn to 3d¹⁰${}^{10}$ in Cu. Their repulsion increases, which tends to enlarge the atom. The two opposite factors balance, so Cu's radius is again 1.17, the same as Mn's. (The elements between them are only slightly smaller.) Copper's 4s¹ and its mass are not the book's reasons for size.

25. Write the electronic configuration of: (a) Cr³⁺$\mathrm{Cr}{}^{3+}$ (₂₄${}_{24}$Cr) (b) Ni²⁺$\mathrm{Ni}{}^{2+}$ (₂₈${}_{28}$Ni)

    Answer: (a) Cr³⁺$\mathrm{Cr}{}^{3+}$: [Ar] 3d³$3d^3$ (from Cr [Ar] 4s¹\,3d⁵$4s^{1}3d^5$: lose the 4s electron, then two 3d electrons). (b) Ni²⁺$\mathrm{Ni}{}^{2+}$: [Ar] 3d⁸$3d^8$ (from Ni [Ar] 4s²\,3d⁸$4s^{2}3d^8$: lose the two 4s electrons).

    Write the atom first. Then remove electrons from 4s first: 4s is the outer level, so it loses electrons first. (a) Cr is [Ar] 4s¹\,3d⁵$4s^{1}3d^5$. Remove the one 4s electron, then two 3d electrons: [Ar] 3d³$3d^3$. (b) Ni is [Ar] 4s²\,3d⁸$4s^{2}3d^8$. Remove the two 4s electrons: [Ar] 3d⁸$3d^8$. Most likely wrong answer: removing 3d electrons first, giving Ni²⁺ as [Ar] 4s²\,3d⁶$4s^{2}3d^6$. Another: Cr³⁺ as [Ar] 4s¹\,3d²$4s^{1}3d^2$, keeping the outer 4s electron.

26. Give reasons: The electronic configuration of copper (₂₉${}_{29}$Cu) is abnormal.

    Answer: Key points: (1) The expected configuration is [Ar] 4s²\,3d⁹$4s^{2}3d^9$. (2) The real one is [Ar] 4s¹\,3d¹⁰$4s^{1}3d^{10}$: one electron is in 3d instead of 4s. (3) A completely filled 3d sublevel (d¹⁰$d^{10}$) gives the atom lower energy and extra stability.

    By the filling pattern, copper would be [Ar] 4s²\,3d⁹$4s^{2}3d^9$. But the real atom is [Ar] 4s¹\,3d¹⁰$4s^{1}3d^{10}$. Now the 3d sublevel is completely filled (d¹⁰$d^{10}$), and 4s is half filled. This arrangement gives the atom lower energy, so it is more stable. Chromium is abnormal for a similar reason: half-filled 3d (d⁵$d^5$). Key words: abnormal configuration, filled d¹⁰$d^{10}$, extra stability. Most likely wrong answer: writing [Ar] 4s²\,3d⁹$4s^{2}3d^9$ and calling it normal.

27. Element X of the first transition series is as rigid as steel but less dense than steel. Which is a use of X?

    • A. Dental implants and artificial joints
    • C. Car springs, added in small amounts to steel
    • B. Mercury vapour lamps for TV photography at night
    • D. Metal plating and leather tanning

    Answer: Dental implants and artificial joints

    Step 1: name X. The book says titanium is as rigid as steel but less dense than steel. So X is titanium. Step 2: recall its uses. Titanium is used in dental implants and artificial joints. It is inert, so the body does not reject it. Its alloys with aluminum are used in aircraft and space shuttles. Scandium is used in mercury vapour lamps. A vanadium-steel alloy is used in car springs, and chromium is used in plating.