Question

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1. complete the following table, by finding the atomic numbers and atomic masses for

each element:

symbol	be	o	al	ar	k	ca	te	i	xe
atomic mass

a. using the data in the table above, determine how the elements in the periodic table are
organized.
(i) atomic mass number \t\t (ii) atomic number.
b. explain your answer providing evidence from the data table.

Explanation:

Part 1: Completing the Table (Atomic Numbers and Atomic Masses)

To complete the table, we refer to the periodic table for each element:

Symbol	Atomic Number	Atomic Mass (approximate, in amu)
O	8	16.00
Al	13	26.98
Ar	18	39.95
K	19	39.10
Ca	20	40.08
Te	52	127.60
I	53	126.90
Xe	54	131.29

Part a: Determining Organization of Periodic Table

Step 1: Analyze Option (i) - Atomic Mass Number

Check the order of atomic masses:

• Be (9.012) → O (16.00) → Al (26.98) → Ar (39.95) → K (39.10) → Ca (40.08) → Te (127.60) → I (126.90) → Xe (131.29)

Here, K (39.10) has a lower atomic mass than Ar (39.95), and I (126.90) has a lower atomic mass than Te (127.60). If organized by atomic mass, this reverse order would occur, which is inconsistent.

Step 2: Analyze Option (ii) - Atomic Number

Check the order of atomic numbers:

• Be (4) → O (8) → Al (13) → Ar (18) → K (19) → Ca (20) → Te (52) → I (53) → Xe (54)

The atomic numbers increase consistently (4 → 8 → 13 → 18 → 19 → 20 → 52 → 53 → 54) with no reversals.

Part b: Explaining the Answer

• Evidence for Atomic Number: The atomic numbers of the elements (4, 8, 13, 18, 19, 20, 52, 53, 54) follow a strictly increasing sequence. For example, after Ar (18) comes K (19), then Ca (20); after Te (52) comes I (53), then Xe (54). This consistent increase matches the periodic table’s organization by atomic number.
• Evidence Against Atomic Mass: Atomic masses show inconsistencies (e.g., K < Ar, I < Te), proving atomic mass is not the primary organizing factor.

Final Answers:

a. The elements in the periodic table are organized by (ii) Atomic number.

b. Explanation: The atomic numbers of the elements (e.g., Be=4, O=8, Al=13, Ar=18, K=19, Ca=20, Te=52, I=53, Xe=54) increase in a consistent, sequential order. In contrast, atomic masses (e.g., K=39.10 < Ar=39.95, I=126.90 < Te=127.60) do not follow a strict increasing order, so atomic number is the correct organizing principle.

Answer:

Part 1: Completing the Table (Atomic Numbers and Atomic Masses)

To complete the table, we refer to the periodic table for each element:

Symbol	Atomic Number	Atomic Mass (approximate, in amu)
O	8	16.00
Al	13	26.98
Ar	18	39.95
K	19	39.10
Ca	20	40.08
Te	52	127.60
I	53	126.90
Xe	54	131.29

Part a: Determining Organization of Periodic Table

Step 1: Analyze Option (i) - Atomic Mass Number

Check the order of atomic masses:

• Be (9.012) → O (16.00) → Al (26.98) → Ar (39.95) → K (39.10) → Ca (40.08) → Te (127.60) → I (126.90) → Xe (131.29)

Here, K (39.10) has a lower atomic mass than Ar (39.95), and I (126.90) has a lower atomic mass than Te (127.60). If organized by atomic mass, this reverse order would occur, which is inconsistent.

Step 2: Analyze Option (ii) - Atomic Number

Check the order of atomic numbers:

• Be (4) → O (8) → Al (13) → Ar (18) → K (19) → Ca (20) → Te (52) → I (53) → Xe (54)

The atomic numbers increase consistently (4 → 8 → 13 → 18 → 19 → 20 → 52 → 53 → 54) with no reversals.

Part b: Explaining the Answer

• Evidence for Atomic Number: The atomic numbers of the elements (4, 8, 13, 18, 19, 20, 52, 53, 54) follow a strictly increasing sequence. For example, after Ar (18) comes K (19), then Ca (20); after Te (52) comes I (53), then Xe (54). This consistent increase matches the periodic table’s organization by atomic number.
• Evidence Against Atomic Mass: Atomic masses show inconsistencies (e.g., K < Ar, I < Te), proving atomic mass is not the primary organizing factor.

Final Answers:

a. The elements in the periodic table are organized by (ii) Atomic number.

b. Explanation: The atomic numbers of the elements (e.g., Be=4, O=8, Al=13, Ar=18, K=19, Ca=20, Te=52, I=53, Xe=54) increase in a consistent, sequential order. In contrast, atomic masses (e.g., K=39.10 < Ar=39.95, I=126.90 < Te=127.60) do not follow a strict increasing order, so atomic number is the correct organizing principle.