Transition Elements · تدريب

كل الأسئلة بإجاباتها · Transition Elements

1. The electrons of an atom stay around its nucleus instead of flying away. Which statement explains this?

   • A. The positive nucleus attracts the negative electrons.
   • D. The electrons attract each other and stay together.
   • C. The neutrons in the nucleus attract the electrons.
   • B. The negative nucleus attracts the negative electrons.

   الإجابة: The positive nucleus attracts the negative electrons.

   There are two kinds of charge: positive and negative. Like charges repel, and unlike charges attract. The nucleus contains protons (positive) and neutrons (no charge). Electrons are negative. So the positive nucleus attracts the negative electrons. The electrons themselves repel each other. You will use both ideas in this chapter: the nucleus attracts electrons, and electrons repel each other.

2. Two electrons are moved closer to each other. What happens to the force between them?

   • B. They repel each other more weakly.
   • C. They start to attract each other.
   • A. They repel each other more strongly.
   • D. There is no force, because they have the same charge.

   الإجابة: They repel each other more strongly.

   Electrons are all negative, so two electrons are like charges and repel each other. The force between charges is stronger when they are closer. So moving the electrons closer makes the repulsion stronger. The book uses this idea: more electrons in 3d means more repulsion between them. This repulsion tends to increase the atomic radius.

3. Which statement about a piece of solid iron is correct?

   • A. It is made of tiny iron atoms that keep vibrating.
   • C. Its particles do not move at all because it is a solid.
   • B. It is one continuous piece with no particles inside.
   • D. It is made of iron molecules, each built from different kinds of atoms.

   الإجابة: It is made of tiny iron atoms that keep vibrating.

   All matter is made of tiny particles. Iron is an element, so it is made of iron atoms only. In a solid, the atoms are packed close together and stay in place. They still keep moving: they vibrate. Later you will meet the metallic bond that holds the atoms of transition metals together.

4. A copper rod gets slightly longer when it is heated. What happens to its atoms?

   • A. They vibrate more, so the spaces between them get slightly bigger.
   • B. Each atom grows bigger.
   • D. The atoms melt and spread out.
   • C. New copper atoms are formed inside the rod.

   الإجابة: They vibrate more, so the spaces between them get slightly bigger.

   Heating gives the atoms more energy, so they vibrate more strongly. They push each other a little further apart. The spaces between atoms grow, so the whole rod gets longer. The atoms themselves keep the same size and number. Remember: a property of the whole metal (expanding, melting) is not a property of one atom.

5. An iron atom is written as ⁵⁶₂₆Fe${}_{26}^{56}\mathrm{Fe}$. How many electrons does this neutral atom contain?

   • D. 82
   • A. 26
   • C. 30
   • B. 56

   الإجابة: 26

   In ^A_ZX${}_Z^A\mathrm{X}$, Z (lower number) is the atomic number = number of protons. A (upper number) is the mass number = protons + neutrons. A neutral atom has as many electrons as protons. So iron has 26 protons and 26 electrons, and 56 - 26 = 30 neutrons. You need the number of electrons to write every electronic configuration in this chapter.

6. A cobalt atom has atomic number 27 and mass number 59. How many neutrons are in its nucleus?

   الإجابة: 32 neutrons

   Mass number = protons + neutrons. Atomic number = protons = 27. Neutrons = mass number - atomic number = 59 - 27 = 32. Common wrong answers: 27 is the number of protons (and electrons). 59 counts protons and neutrons together. 86 comes from adding the two numbers. Key words: atomic number = number of protons; mass number = protons + neutrons.

7. What is the greatest number of electrons the third main energy level (M, n = 3$n=3$) can hold?

   • A. 18
   • C. 9
   • D. 6
   • B. 8

   الإجابة: 18

   A main energy level n$n$ holds at most 2n²$2n^2$ electrons. K (n = 1$n=1$): 2. L (n = 2$n=2$): 8. M (n = 3$n=3$): 18. N (n = 4$n=4$): 32. The M level can take 18 because it contains the 3d sublevel. This matters in this chapter: the first transition series fills the 3d sublevel, which is part of the third level.

8. Which shows the correct distribution of the 20 electrons of calcium (₂₀${}_{20}$Ca) in its main energy levels?

   • B. 2, 8, 10
   • A. 2, 8, 8, 2
   • D. 8, 8, 4
   • C. 2, 18

   الإجابة: 2, 8, 8, 2

   Calcium has 20 electrons. K takes 2 and L takes 8. M takes 8 (3s and 3p). The last 2 go to the N level (4s), not to the 3d of level M. So the distribution is 2, 8, 8, 2. The book starts the first transition series right after calcium. From scandium on, the 3d sublevel of level M fills.

9. What is the chemical symbol of iron?

   • D. F
   • C. Ir
   • A. Fe
   • B. I

   الإجابة: Fe

   Iron's symbol is Fe, from the Latin ferrum. Some other symbols in this chapter also come from Latin: copper is Cu (cuprum). A symbol has one capital letter, sometimes followed by one small letter. You will see Fe on almost every page of this chapter.

10. Which formula represents an element (one kind of atom only), not a compound?

    • B. CO$\mathrm{CO}$
    • A. Co$\mathrm{Co}$
    • D. Fe2O3$\mathrm{Fe}{}_2\mathrm{O}{}_3$
    • C. CuO$\mathrm{CuO}$

    الإجابة: Co$\mathrm{Co}$

    An element is made of one kind of atom, so its formula has one symbol. Each symbol starts with a capital letter; a small letter belongs to the same symbol. Co (cobalt) is one symbol. CO is two symbols, C and O: carbon monoxide, a compound. CuO and Fe2O3$\mathrm{Fe}{}_2\mathrm{O}{}_3$ are compounds of a metal with oxygen. Read capitals carefully: Co and CO are very different.

11. Representative elements in the same group (vertical column) have similar chemical properties. Why?

    • B. They have the same number of main energy levels.
    • D. They have the same number of protons.
    • C. They have the same atomic mass.
    • A. They have the same number of electrons in the outer energy level.

    الإجابة: They have the same number of electrons in the outer energy level.

    A period is a horizontal row. Its elements have the same number of main energy levels. A group is a vertical column. For the representative elements, a group shares the same number of outer electrons. Chemical properties depend mainly on outer electrons, so a group shares similar properties. In this chapter you will meet group VIII, where elements resemble their horizontal neighbours more. Keep the normal rule in mind first.

12. The electrons of potassium (₁₉${}_{19}$K) are distributed as 2, 8, 8, 1. In which period is potassium?

    • C. The third period
    • A. The fourth period
    • B. The first period

    الإجابة: The fourth period

    The period number equals the number of main energy levels that contain electrons. Potassium has electrons in K, L, M and N: four levels, so it is in the fourth period. Its single outer electron puts it in group 1 (IA). The first transition series is also in the fourth period, right after potassium and calcium.

13. Which sublevels make up the third main energy level (n = 3$n=3$)?

    • B. 3s, 3p, 3d and 3f
    • C. 3s and 3p only
    • A. 3s, 3p and 3d

    الإجابة: 3s, 3p and 3d

    A main energy level n$n$ contains n$n$ sublevels. Level 1: 1s. Level 2: 2s, 2p. Level 3: 3s, 3p, 3d. Level 4: 4s, 4p, 4d, 4f. So the d sublevel first appears at n = 3$n=3$. The 3d sublevel is the one filled in the first transition series.

14. Which of the following sublevels cannot exist?

    • A. 2d
    • C. 4f
    • D. 5d
    • B. 3d

    الإجابة: 2d

    Level n$n$ has n$n$ sublevels: level 2 has s and p only, so 2d cannot exist. 3d exists in level 3, 4f in level 4, and 5d in level 5. The transition series use 3d, 4d, 5d and 6d. They never use 1d or 2d.

15. How many orbitals are there in a d sublevel?

    • A. 5
    • D. 7
    • B. 10
    • C. 3

    الإجابة: 5

    Number of orbitals: s = 1, p = 3, d = 5, f = 7. Each orbital holds at most 2 electrons. So a d sublevel holds 5 × 2 = 10$5\times 2=10$ electrons. You will draw these five d orbitals as five boxes in this chapter.

16. Which statement describes an orbital correctly?

    • A. A region around the nucleus where an electron is most likely found; it holds up to 2 electrons.
    • C. A region around the nucleus where an electron is most likely found; it holds up to 8 electrons.
    • B. A fixed circular path around the nucleus; it holds up to 2 electrons.
    • D. A fixed circular path around the nucleus; it holds up to 8 electrons.

    الإجابة: A region around the nucleus where an electron is most likely found; it holds up to 2 electrons.

    An orbital is a region of space around the nucleus where the electron is most likely to be found. It is not a circular path. Each orbital holds at most 2 electrons, with opposite spins. In the book, each orbital is drawn as a box: ↑ for one electron, ↑↓ for two.

17. Arrange these sublevels in the order in which electrons fill them (Aufbau principle), first to last.

    الإجابة: 3s → 3p → 4s → 3d → 4p

    By the Aufbau principle, electrons fill sublevels in this order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, ... So the order here is 3s, 3p, 4s, 3d, 4p. Most common mistake: putting 3d right after 3p because 3 comes before 4. This order explains why calcium ends with 4s², and the first transition series then fills 3d.

18. Argon (₁₈${}_{18}$Ar) has the configuration 1s²\,2s²\,2p⁶\,3s²\,3p⁶$1s^{2}2s^{2}2p^{6}3s^{2}3p^6$. Which sublevel receives the 19th electron in potassium (₁₉${}_{19}$K)?

    • C. 4p
    • A. 4s
    • B. 3d
    • D. 3p

    الإجابة: 4s

    3p is full at argon (3p⁶$3p^6$). By the Aufbau principle, the order after 3p is 4s, then 3d, then 4p. So the 19th electron goes into 4s: K is [Ar]\,4s¹$[\mathrm{Ar}]4s^1$. Remember this order: 3d starts filling only after 4s, from scandium onwards.

19. An ordinary bar magnet is brought near each object. Which object is clearly pulled toward it?

    • A. An iron nail
    • C. A plastic ruler rubbed with a cloth
    • B. A copper wire

    الإجابة: An iron nail

    A magnet has a magnetic field around it. It strongly attracts some materials, like iron, cobalt and nickel. Most metals, such as copper, are not clearly pulled. A rubbed ruler is charged; that is electricity, not magnetism. In this chapter you will see that some substances are only weakly attracted to an external magnetic field.

20. The south pole of magnet A attracts end X of magnet B. What is end X?

    • B. A south pole
    • C. It could be either pole, because a magnet attracts both
    • A. A north pole

    الإجابة: A north pole

    Every magnet has a north and a south pole. Like poles repel, and unlike poles attract. End X is attracted to a south pole, so it must be a north pole. So a magnetic field can attract or repel. In this chapter, paramagnetic substances are attracted to an external field and diamagnetic ones are repelled.

21. Two electrons occupy the same orbital. Which statement is correct?

    • D. They spin in opposite directions, so their magnetic effects add up.
    • B. They spin in the same direction, so their magnetic effects add up.
    • A. They spin in opposite directions, so their magnetic effects cancel.
    • C. They stop spinning, because the orbital is full.

    الإجابة: They spin in opposite directions, so their magnetic effects cancel.

    Each electron spins and acts like a tiny magnet. By the Pauli principle, two electrons in one orbital must have opposite spins (↑↓). Opposite spins cancel each other's magnetic effect. The book uses this idea: when all electrons are paired, the magnetic moment equals zero (diamagnetic).

22. What is the greatest number of electrons in one d sublevel that can all spin in the same direction?

    • A. 5
    • C. 2
    • B. 10

    الإجابة: 5

    A d sublevel has 5 orbitals. By the Pauli principle, an orbital can hold two electrons only with opposite spins. So each orbital can give at most one electron spinning ↑. With 5 orbitals, at most 5 electrons can spin the same way. That is why a d⁵$d^5$ sublevel has 5 unpaired electrons, the greatest possible number.

23. Which is the correct electronic configuration of calcium (₂₀${}_{20}$Ca)?

    • C. 1s²\,2s²\,2p⁶\,3s²\,3p⁸$1s^{2}2s^{2}2p^{6}3s^{2}3p^8$
    • A. 1s²\,2s²\,2p⁶\,3s²\,3p⁶\,4s²$1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^2$
    • D. 1s²\,2s²\,2p⁶\,3s²\,3p⁶\,3d¹\,4s¹$1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{1}4s^1$
    • B. 1s²\,2s²\,2p⁶\,3s²\,3p⁶\,3d²$1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^2$

    الإجابة: 1s²\,2s²\,2p⁶\,3s²\,3p⁶\,4s²$1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^2$

    Fill in the Aufbau order. Respect each capacity: s = 2, p = 6, d = 10. 1s²\,2s²\,2p⁶\,3s²\,3p⁶$1s^{2}2s^{2}2p^{6}3s^{2}3p^6$ uses 18 electrons. The last 2 go to 4s. Short form: [Ar]\,4s²$[\mathrm{Ar}]4s^2$. This is exactly where the book starts the first transition series: after calcium, 3d begins to fill.

24. Which is the correct short (noble-gas core) configuration of gallium (₃₁${}_{31}$Ga)?

    • C. [Ar]\,4s²\,3d¹¹$[\mathrm{Ar}]4s^{2}3d^{11}$
    • A. [Ar]\,4s²\,3d¹⁰\,4p¹$[\mathrm{Ar}]4s^{2}3d^{10}4p^1$
    • B. [Ar]\,4s²\,4p¹$[\mathrm{Ar}]4s^{2}4p^1$
    • D. [Kr]\,4s²\,3d¹⁰\,4p¹$[\mathrm{Kr}]4s^{2}3d^{10}4p^1$

    الإجابة: [Ar]\,4s²\,3d¹⁰\,4p¹$[\mathrm{Ar}]4s^{2}3d^{10}4p^1$

    Step 1: take the noble gas before gallium: argon, 18 electrons. Step 2: 31 - 18 = 13 electrons remain. Step 3: fill in the Aufbau order: 4s (2), then 3d (10), then 4p (1). So Ga is [Ar]\,4s²\,3d¹⁰\,4p¹$[\mathrm{Ar}]4s^{2}3d^{10}4p^1$. Always check the total and each sublevel's capacity.

25. Classify each element into its block, using the sublevel that receives its last electron.

    الإجابة: d-block: ₂₃${}_{23}$V: [Ar]\,4s²\,3d³$[\mathrm{Ar}]4s^{2}3d^3$, ₃₀${}_{30}$Zn: [Ar]\,4s²\,3d¹⁰$[\mathrm{Ar}]4s^{2}3d^{10}$ · p-block: ₁₇${}_{17}$Cl: [Ne]\,3s²\,3p⁵$[\mathrm{Ne}]3s^{2}3p^5$ · s-block: ₁₁${}_{11}$Na: [Ne]\,3s¹$[\mathrm{Ne}]3s^1$, ₂₀${}_{20}$Ca: [Ar]\,4s²$[\mathrm{Ar}]4s^2$

    The block is the sublevel that receives the last electron in the Aufbau order. Na (3s¹$3s^1$) and Ca (4s²$4s^2$): s-block. Cl (3p⁵$3p^5$): p-block. V (3d³$3d^3$) and Zn (3d¹⁰$3d^{10}$): d-block. Common mistake 1: putting V in the s-block because 4s is written first. Common mistake 2: putting Zn outside the d-block because its 3d is full. Zn is a d-block element, even though the book does not count it as a transition element.

26. Bromine (₃₅${}_{35}$Br) has the configuration [Ar]\,4s²\,3d¹⁰\,4p⁵$[\mathrm{Ar}]4s^{2}3d^{10}4p^5$. In which block is bromine?

    • B. The d-block
    • C. The s-block
    • A. The p-block

    الإجابة: The p-block

    The block is decided by the sublevel that receives the last electron. For bromine, 4s fills, then 3d, then 4p. The last electron enters 4p, so bromine is in the p-block. A full 3d¹⁰$3d^{10}$ inside the atom does not make it a d-block element.

27. Choose the correct answer: In the long form of the periodic table, the main transition elements occupy ...

    • B. the right side of the table, after the p-block
    • C. the two separate rows below the main table
    • D. the left side of the table, before the s-block
    • A. the middle of the table, between the s-block and the p-block

    الإجابة: the middle of the table, between the s-block and the p-block

    The book: the transition elements occupy the middle of the periodic table, between the (s) and (p) blocks. They are more than 60 elements. They are classified into main transition elements (d-block) and inner transition elements (f-block). The two rows under the table are the inner transition elements, which this chapter does not study.

28. Choose the correct answer: The d-block of the periodic table contains ...

    • B. 5 vertical columns, because the d sublevel has 5 orbitals
    • C. 8 vertical columns, because there are 8 B groups (IIIB to IIB)
    • A. 10 vertical columns, because the d sublevel can take up to 10 electrons

    الإجابة: 10 vertical columns, because the d sublevel can take up to 10 electrons

    In the main transition elements, electrons occupy the d sublevel in sequence. The d sublevel can take up to ten electrons, so the d-block contains ten vertical columns. The first column ends with ns²\,(n-1)d¹$n{s}^2(n-1)d^1$; the last ends with ns²\,(n-1)d¹⁰$n{s}^2(n-1)d^{10}$. There are 8 group labels only because group VIII alone takes three columns (8, 9, 10).

29. Choose the correct answer: The second transition series includes the elements in which the ... sublevel is filled successively, and it lies in the ... period.

    • A. 4d ... fifth
    • D. 2d ... second
    • B. 5d ... fifth
    • C. 4d ... fourth

    الإجابة: 4d ... fifth

    The four series fill (n-1)d$(n-1)d$, one level below the period number n$n$. First series: 3d, period 4 (Sc to Zn). Second series: 4d, period 5 (Y to Cd). Third series: 5d, period 6 (La to Hg). Fourth series: 6d, period 7. Key words from the book: 'the sublevel (4d) is filled successively', 'found in the fifth period'.

30. Choose the correct answer: The first transition series starts with ... and ends with ...

    • C. titanium (₂₂${}_{22}$Ti) ... zinc (₃₀${}_{30}$Zn)
    • A. scandium (₂₁${}_{21}$Sc) ... zinc (₃₀${}_{30}$Zn)
    • D. calcium (₂₀${}_{20}$Ca) ... zinc (₃₀${}_{30}$Zn)
    • B. scandium (₂₁${}_{21}$Sc) ... copper (₂₉${}_{29}$Cu)

    الإجابة: scandium (₂₁${}_{21}$Sc) ... zinc (₃₀${}_{30}$Zn)

    The first transition series includes the elements in which the 3d sublevel is filled successively. It is in the fourth period after calcium. It has ten elements: Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn. It starts with scandium (₂₁${}_{21}$Sc, 4s²\,3d¹$4s^{2}3d^1$) and ends with zinc (₃₀${}_{30}$Zn, 4s²\,3d¹⁰$4s^{2}3d^{10}$). Note: zinc belongs to the series even though the book does not consider it a transition element.

31. Compare: classify each description as belonging to the main transition elements or the inner transition elements.

    الإجابة: Main transition elements: Their atoms fill the 4d sublevel, The elements of the first transition series, The elements studied in this chapter · Inner transition elements: Their atoms fill the 4f sublevel, The lanthanides, Their atoms fill the 5f sublevel

    The transition elements are classified into two classes. Main transition elements (d-block): their atoms fill a d sublevel (3d, 4d, 5d, 6d). They form the four transition series, and this chapter studies them only. Inner transition elements (f-block): their atoms fill an f sublevel (4f = lanthanides, 5f = actinides). They are the two rows under the table. Most common mistake: counting the lanthanides as main transition elements because the lanthanides and actinides lie in periods 6 and 7.

32. Arrange the following groups of the d-block from left to right as they appear in the periodic table.

    الإجابة: IIIB → VB → VIIB → VIII → IB → IIB

    From left to right the d-block groups are: IIIB (3), IVB (4), VB (5), VIB (6), VIIB (7), VIII (8, 9, 10), IB (11), IIB (12). So the order here is IIIB, VB, VIIB, VIII, IB, IIB. Most common mistake: putting IB and IIB first because 'I' and 'II' are smaller numbers. Use the modern numbers 3 to 12 to check yourself.

33. Rutherfordium (₁₀₄${}_{104}$Rf) lies in the seventh period. Its configuration ends with 5f¹⁴\,7s²\,6d²$5f^{14}7s^{2}6d^2$. To which group of elements does it belong?

    • B. The seventh transition series
    • D. The sixth transition series, because it fills 6d
    • C. The inner transition elements, because it contains 5f¹⁴$5f^{14}$
    • A. The fourth transition series

    الإجابة: The fourth transition series

    Rf's last electrons enter 6d: 7s²\,6d²$7s^{2}6d^2$. The 5f¹⁴$5f^{14}$ is complete, so it does not decide the block. The book: in the fourth transition series, the 6d sublevel is filled successively. These elements are found in the seventh period. Link: 3d = first, 4d = second, 5d = third, 6d = fourth. Neither the period number (7) nor the sublevel number (6) is the series number.

34. element	Sc	Ti	V	Cr	Mn	Fe	Co	Ni	Cu	Zn
    % wt	0.0026	0.66	0.02	0.014	0.11	5	0.003	0.0089	0.0068	0.0078

    The table shows the percent of each element of the first transition series in the earth's crust. Which statement is correct?

    • A. Iron is the most abundant, and scandium is the least abundant.
    • C. The percent decreases steadily from Sc to Zn as the atomic number increases.
    • B. Iron is the most abundant, and cobalt is the least abundant.
    • D. Cobalt has a very small percent, so it has little economic importance.

    الإجابة: Iron is the most abundant, and scandium is the least abundant.

    Read each value from the table. Iron (5) is by far the largest. The smallest is scandium (0.0026), just below cobalt (0.003 = 0.0030). The values go up and down across the series, for example Ti 0.66 and V 0.02. So there is no steady trend. The book adds: together these elements form only nearly 7% of the crust, but they have high economic importance. Tip: to compare decimals, write them with the same number of digits.

35. The configurations of three elements end as follows: ₇₂${}_{72}$X: 6s²\,4f¹⁴\,5d²$6s^{2}4f^{14}5d^2$ ₆₃${}_{63}$Y: 6s²\,4f⁷$6s^{2}4f^7$ ₃₁${}_{31}$Z: 4s²\,3d¹⁰\,4p¹$4s^{2}3d^{10}4p^1$ Consider the following statements: (I) X is an inner transition element, because its atom contains a full 4f sublevel. (II) Y is an inner transition element. (III) Z is a main transition element, because its atom contains a full 3d sublevel. Which of these statements is/are correct?

    • A. II only
    • D. I, II and III
    • C. II and III only
    • B. I and II only

    الإجابة: II only

    Classify an element by the sublevel its electrons are filling, the last one in the configuration. (I) Wrong: X has a full 4f sublevel, but its electrons are now filling 5d (5d²$5d^2$). So X is a main transition element (d-block, third transition series). (II) Correct: Y is filling the 4f sublevel, so it is an inner transition element (f-block, a lanthanide). (III) Wrong: Z has a full 3d sublevel, but its last electron enters 4p. So Z is a p-block element, not a transition element. Answer: II only. Key idea: main transition elements fill a d sublevel; inner transition elements fill an f sublevel.

36. Element X lies in the sixth period. Its configuration ends with 4f¹⁴\,6s²\,5d⁶$4f^{14}6s^{2}5d^6$. Which choice gives the group of X and the elements X resembles most?

    • D. Group VIB; it resembles the element below it more than its horizontal neighbours
    • B. Group VIII; it resembles the element below it more than its horizontal neighbours
    • C. Group VIB; it resembles its horizontal neighbours more than the element below it
    • A. Group VIII; it resembles its horizontal neighbours more than the element below it

    الإجابة: Group VIII; it resembles its horizontal neighbours more than the element below it

    Step 1 (find the column): X fills 5d, so it is in the d-block (third series). The 4f¹⁴ is complete and does not decide the block. The columns run from d¹$d^1$ (IIIB) to d¹⁰$d^{10}$ (IIB): d¹$d^1$ IIIB, d²$d^2$ IVB, d³$d^3$ VB, d⁴$d^4$ VIB, d⁵$d^5$ VIIB, d⁶$d^6$ VIII. So X is in the first column of group VIII (column 8). Step 2 (the property): group VIII is special. The book says its elements are similar horizontally more than the elements below them. Most common mistake: taking the number of d electrons (6) as the group number, which gives VIB.

37. The configurations of three elements end as follows: ₂₅${}_{25}$X: 4s²\,3d⁵$4s^{2}3d^5$ ₄₃${}_{43}$Y: 5s²\,4d⁵$5s^{2}4d^5$ ₇₃${}_{73}$Z: 6s²\,4f¹⁴\,5d³$6s^{2}4f^{14}5d^3$ Consider the following statements: (I) X and Y belong to different transition series, although both have five electrons in their d sublevel. (II) Y lies in the fourth period, because its atom fills the 4d sublevel. (III) Z belongs to the third transition series and lies in the sixth period. Which of these statements is/are correct?

    • C. III only
    • D. I, II and III
    • B. I and II only
    • A. I and III only

    الإجابة: I and III only

    (I) holds: X fills 3d, so it is in the first transition series; Y fills 4d, so it is in the second transition series. Having five d electrons each does not put them in the same series. (II) does not hold: Y's outer sublevel is 5s, so it lies in the fifth period. The second transition series fills 4d and lies in the fifth period. (III) holds: Z fills 5d (its 4f is already full), so it is in the third transition series, in the sixth period. Answer: I and III only. Rule for the transition series: the series in period n$n$ fills the (n-1)d$(n-1)d$ sublevel.

38. Element X belongs to the first transition series. Its atomic number is 4 more than that of the first element of this series. The symbol of X is ...

    • C. Cr
    • A. Mn
    • B. Mg
    • D. Fe

    الإجابة: Mn

    Step 1: the first element of the first transition series is scandium, ₂₁${}_{21}$Sc. Step 2: 21 + 4 = 25. In order: Sc 21, Ti 22, V 23, Cr 24, Mn 25, Fe 26, Co 27, Ni 28, Cu 29, Zn 30. So X is manganese, Mn. Common errors: starting the series at Ti (gives Fe), swapping Cr and Mn, or writing Mg (magnesium) for manganese.