DP Chemistry (first assessment 2025)

Syllabus sections »

Structure 3. Classification of matter » Structure 3.1—The periodic table: Classification of elements

Structure 3.1—The periodic table: Classification of elements

Description

[N/A]

Directly related questions

22N.1A.SL.TZ0.6:
What is the relative atomic mass of a sample of chlorine containing 70 % of the ³⁵Cl isotope and 30 % of the ³⁷Cl isotope?

A. 35.4

B. 35.5

C. 35.6

D. 35.7
22N.1A.SL.TZ0.6:
What is the relative atomic mass of a sample of chlorine containing 70 % of the ³⁵Cl isotope and 30 % of the ³⁷Cl isotope?

A. 35.4

B. 35.5

C. 35.6

D. 35.7
22N.1A.SL.TZ0.7:
Which elements are considered to be metalloids?

I. Gallium

II. Germanium

III. Arsenic

A. I and II only

B. I and III only

C. II and III only

D. I, II and III
22N.1A.SL.TZ0.7:
Which elements are considered to be metalloids?

I. Gallium

II. Germanium

III. Arsenic

A. I and II only

B. I and III only

C. II and III only

D. I, II and III
22N.1A.SL.TZ0.8: Which property of elements increases down a group but decreases across a period? A. Atomic...
22N.1A.SL.TZ0.8: Which property of elements increases down a group but decreases across a period? A. Atomic...
22N.2.SL.TZ0.5b:
Write an equation that shows how sulfur dioxide can produce acid rain.
22N.2.SL.TZ0.5b:
Write an equation that shows how sulfur dioxide can produce acid rain.
22N.2.SL.TZ0.b:
Write an equation that shows how sulfur dioxide can produce acid rain.
19M.1A.HL.TZ1.10:
What is the IUPAC name of NiCO₃?

A. nickel(II) carbonate

B. nickel carbonate

C. nickel(I) carbonate

D. nitrogen(I) carbonate
19M.1A.HL.TZ1.10:
What is the IUPAC name of NiCO₃?

A. nickel(II) carbonate

B. nickel carbonate

C. nickel(I) carbonate

D. nitrogen(I) carbonate
19M.1A.HL.TZ1.10:
What is the IUPAC name of NiCO₃?

A. nickel(II) carbonate

B. nickel carbonate

C. nickel(I) carbonate

D. nitrogen(I) carbonate
19M.1A.HL.TZ1.10:
What is the IUPAC name of NiCO₃?

A. nickel(II) carbonate

B. nickel carbonate

C. nickel(I) carbonate

D. nitrogen(I) carbonate
19M.2.SL.TZ2.4e(i):
Suggest why the existence of salts containing an ion with this formula could be predicted. Refer to section 7 of the data booklet.
19M.2.SL.TZ2.4e(i):
Suggest why the existence of salts containing an ion with this formula could be predicted. Refer to section 7 of the data booklet.
19M.2.SL.TZ2.e(i):
Suggest why the existence of salts containing an ion with this formula could be predicted. Refer to section 7 of the data booklet.

Sub sections and their related questions

Structure 3.1.1—The periodic table consists of periods, groups and blocks. Identify the positions of metals, metalloids and non-metals in the periodic table.

22M.2.SL.TZ1.1a(ii): State the block of the periodic table in which magnesium is located.
22M.1A.SL.TZ2.8: Which element is found in the 4th group, 6th period of the periodic table? A. Selenium B....
19N.1A.SL.TZ0.8: Which is an f-block element? A. Sc B. Sm C. Sn D. Sr
21M.1A.SL.TZ2.8:
Which is a d-block element?

A. Ca

B. Cf

C. C $l$

D. Co
22N.1A.SL.TZ0.7:
Which elements are considered to be metalloids?

I. Gallium

II. Germanium

III. Arsenic

A. I and II only

B. I and III only

C. II and III only

D. I, II and III
22M.2.SL.TZ1.1a(ii): State the block of the periodic table in which magnesium is located.
22M.2.SL.TZ1.a(ii): State the block of the periodic table in which magnesium is located.
22M.1A.SL.TZ2.8: Which element is found in the 4th group, 6th period of the periodic table? A. Selenium B....
19N.1A.SL.TZ0.8: Which is an f-block element? A. Sc B. Sm C. Sn D. Sr
21M.1A.SL.TZ2.8:
Which is a d-block element?

A. Ca

B. Cf

C. C $l$

D. Co
22N.1A.SL.TZ0.7:
Which elements are considered to be metalloids?

I. Gallium

II. Germanium

III. Arsenic

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

Structure 3.1.2—The period number shows the outer energy level that is occupied by electrons. Elements in a group have a common number of valence electrons. Deduce the electron configuration of an atom up to Z = 36 from the element’s position in the periodic table and vice versa.

19M.1A.SL.TZ1.6:
Which describes an atom of bismuth, Bi (Z = 83)?
19M.1A.SL.TZ1.7:
Which describes an atom of bismuth, Bi (Z = 83)?
22M.1A.SL.TZ1.8:
Which of the following is the electron configuration of a metallic element?

A. [Ne] 3s² 3p²

B. [Ne] 3s² 3p⁴

C. [Ne] 3s² 3p⁶ 3d³ 4s²

D. [Ne] 3s² 3p⁶ 3d¹⁰ 4s² 4p⁵
21M.1A.SL.TZ1.7: Which species has the same electron configuration as argon? A. Br− B. Ca2+ C. Al3+ D. Si4+
19M.1A.SL.TZ1.6:
Which describes an atom of bismuth, Bi (Z = 83)?
19M.1A.SL.TZ1.7:
Which describes an atom of bismuth, Bi (Z = 83)?
22M.1A.SL.TZ1.8:
Which of the following is the electron configuration of a metallic element?

A. [Ne] 3s² 3p²

B. [Ne] 3s² 3p⁴

C. [Ne] 3s² 3p⁶ 3d³ 4s²

D. [Ne] 3s² 3p⁶ 3d¹⁰ 4s² 4p⁵
21M.1A.SL.TZ1.7: Which species has the same electron configuration as argon? A. Br− B. Ca2+ C. Al3+ D. Si4+

Structure 3.1.3—Periodicity refers to trends in properties of elements across a period and down a group.

22M.2.SL.TZ2.2a:
Explain why the first ionization energy of calcium is greater than that of potassium.
22M.1A.SL.TZ2.7: Three elements, X, Y, and Z are in the same period of the periodic table. The relative sizes of...
22M.1A.SL.TZ2.5: What is the correct order for increasing first ionization energy? A. Na < Mg < Al B. Na...
19M.2.SL.TZ2.4b(i):
Suggest the basis of these predictions.
19M.2.SL.TZ2.3b(iii):
Predict, giving two reasons, how the first ionization energy of ¹⁵N compares with that of ¹⁴N.
19M.2.SL.TZ2.4a:
Before its isolation, scientists predicted the existence of rhenium and some of its properties.

Suggest the basis of these predictions.
19M.1A.SL.TZ1.7: Which series represents atoms in order of decreasing atomic radius? A. N > C > Be >...
19M.1A.SL.TZ2.7: How do the following properties change down Group 17 of the periodic table?
19M.1A.SL.TZ1.8: What are typical characteristics of metals?
19M.1A.SL.TZ2.8: How do the following properties change down Group 17 of the periodic table?
19M.2.SL.TZ2.3b(iii):
Predict, giving two reasons, how the first ionization energy of ¹⁵N compares with that of ¹⁴N.
19N.1A.SL.TZ0.7: Which property shows a general increase from left to right across period 2, Li to F? A. Melting...
21M.1A.SL.TZ1.8: Which trend is correct, going down group 1? A. Melting point increases B. Reactivity...
21M.2.SL.TZ2.2a(i): Explain why Si has a smaller atomic radius than Al.
21M.2.SL.TZ1.1b:
Justify why sulfur is classified as a non-metal by giving two of its chemical properties.
21M.1A.SL.TZ2.7: Which property increases down group 1? A. atomic radius B. electronegativity C. first...
21M.1A.SL.TZ2.16:
Which represents electron affinity?

A. Al²⁺(g) → Al³⁺(g) + e⁻

B. C (g) + e⁻ → C⁻(g)

C. Cl₂(g) → 2Cl (g)

D. S (s) → S⁺(g) + e⁻
21M.2.SL.TZ1.1b:
Justify why sulfur is classified as a non-metal by giving two of its chemical properties.
20N.1A.SL.TZ0.7:
Which of the following shows a general increase across period 3 from $Na$ to $Cl$ ?

A. Ionic radius

B. Atomic radius

C. Ionization energy

D. Melting point
21N.2.SL.TZ0.2: Explain the general increase in trend in the first ionization energies of the period 3 elements,...
22N.1A.SL.TZ0.8: Which property of elements increases down a group but decreases across a period? A. Atomic...
22M.2.SL.TZ2.2a:
Explain why the first ionization energy of calcium is greater than that of potassium.
22M.2.SL.TZ2.a:
Explain why the first ionization energy of calcium is greater than that of potassium.
22M.1A.SL.TZ2.7: Three elements, X, Y, and Z are in the same period of the periodic table. The relative sizes of...
22M.1A.SL.TZ2.5: What is the correct order for increasing first ionization energy? A. Na < Mg < Al B. Na...
19M.2.SL.TZ2.4b(i):
Suggest the basis of these predictions.
19M.2.SL.TZ2.b(i):
Suggest the basis of these predictions.
19M.2.SL.TZ2.3b(iii):
Predict, giving two reasons, how the first ionization energy of ¹⁵N compares with that of ¹⁴N.
19M.2.SL.TZ2.b(iii):
Predict, giving two reasons, how the first ionization energy of ¹⁵N compares with that of ¹⁴N.
19M.2.SL.TZ2.4a:
Before its isolation, scientists predicted the existence of rhenium and some of its properties.

Suggest the basis of these predictions.
19M.2.SL.TZ2.a:
Before its isolation, scientists predicted the existence of rhenium and some of its properties.

Suggest the basis of these predictions.
19M.1A.SL.TZ1.7: Which series represents atoms in order of decreasing atomic radius? A. N > C > Be >...
19M.1A.SL.TZ2.7: How do the following properties change down Group 17 of the periodic table?
19M.1A.SL.TZ1.8: What are typical characteristics of metals?
19M.1A.SL.TZ2.8: How do the following properties change down Group 17 of the periodic table?
19M.2.SL.TZ2.3b(iii):
Predict, giving two reasons, how the first ionization energy of ¹⁵N compares with that of ¹⁴N.
19M.2.SL.TZ2.b(iii):
Predict, giving two reasons, how the first ionization energy of ¹⁵N compares with that of ¹⁴N.
19N.1A.SL.TZ0.7: Which property shows a general increase from left to right across period 2, Li to F? A. Melting...
21M.1A.SL.TZ1.8: Which trend is correct, going down group 1? A. Melting point increases B. Reactivity...
21M.2.SL.TZ2.2a(i): Explain why Si has a smaller atomic radius than Al.
21M.2.SL.TZ2.a(i): Explain why Si has a smaller atomic radius than Al.
21M.2.SL.TZ1.1b:
Justify why sulfur is classified as a non-metal by giving two of its chemical properties.
21M.2.SL.TZ1.b:
Justify why sulfur is classified as a non-metal by giving two of its chemical properties.
21M.1A.SL.TZ2.7: Which property increases down group 1? A. atomic radius B. electronegativity C. first...
21M.1A.SL.TZ2.16:
Which represents electron affinity?

A. Al²⁺(g) → Al³⁺(g) + e⁻

B. C (g) + e⁻ → C⁻(g)

C. Cl₂(g) → 2Cl (g)

D. S (s) → S⁺(g) + e⁻
21M.2.SL.TZ1.1b:
Justify why sulfur is classified as a non-metal by giving two of its chemical properties.
21M.2.SL.TZ1.b:
Justify why sulfur is classified as a non-metal by giving two of its chemical properties.
20N.1A.SL.TZ0.7:
Which of the following shows a general increase across period 3 from $Na$ to $Cl$ ?

A. Ionic radius

B. Atomic radius

C. Ionization energy

D. Melting point
21N.2.SL.TZ0.2: Explain the general increase in trend in the first ionization energies of the period 3 elements,...
22N.1A.SL.TZ0.8: Which property of elements increases down a group but decreases across a period? A. Atomic...

Structure 3.1.4—Trends in properties of elements down a group include the increasing metallic character of group 1 elements and decreasing non-metallic character of group 17 elements. Describe and explain the reactions of group 1 metals with water, and of group 17 elements with halide ions.

22M.2.SL.TZ1.5d(iv): The polarity of the carbon–halogen bond, C–X, facilitates attack by HO–. Outline, giving a...
22M.2.SL.TZ1.3f(iii): The polarity of the carbon–halogen bond, C–X, facilitates attack by HO–. Outline, giving a...
22M.1A.SL.TZ2.7: Three elements, X, Y, and Z are in the same period of the periodic table. The relative sizes of...
22M.1A.SL.TZ2.6: Which are the most reactive elements of the alkali metals and halogens? A. Lithium and...
21N.1A.SL.TZ0.7: Which element has the highest metallic character in Group 14? A. C B. Si C. Ge D. Sn
19N.2.SL.TZ0.6b:
Another airbag reactant produces nitrogen gas and sodium.

Suggest, including an equation, why the products of this reactant present a safety hazard.
20N.1A.SL.TZ0.6: What is the correct trend going down groups 1 and 17? A. Melting points increase B. Boiling...
22M.1A.SL.TZ1.8:
Which of the following is the electron configuration of a metallic element?

A. [Ne] 3s² 3p²

B. [Ne] 3s² 3p⁴

C. [Ne] 3s² 3p⁶ 3d³ 4s²

D. [Ne] 3s² 3p⁶ 3d¹⁰ 4s² 4p⁵
22M.2.SL.TZ1.5d(iv): The polarity of the carbon–halogen bond, C–X, facilitates attack by HO–. Outline, giving a...
22M.2.SL.TZ1.d(iv): The polarity of the carbon–halogen bond, C–X, facilitates attack by HO–. Outline, giving a...
22M.2.SL.TZ1.3f(iii): The polarity of the carbon–halogen bond, C–X, facilitates attack by HO–. Outline, giving a...
22M.2.SL.TZ1.f(iii): The polarity of the carbon–halogen bond, C–X, facilitates attack by HO–. Outline, giving a...
22M.1A.SL.TZ2.7: Three elements, X, Y, and Z are in the same period of the periodic table. The relative sizes of...
22M.1A.SL.TZ2.6: Which are the most reactive elements of the alkali metals and halogens? A. Lithium and...
21N.1A.SL.TZ0.7: Which element has the highest metallic character in Group 14? A. C B. Si C. Ge D. Sn
19N.2.SL.TZ0.6b:
Another airbag reactant produces nitrogen gas and sodium.

Suggest, including an equation, why the products of this reactant present a safety hazard.
19N.2.SL.TZ0.b:
Another airbag reactant produces nitrogen gas and sodium.

Suggest, including an equation, why the products of this reactant present a safety hazard.
20N.1A.SL.TZ0.6: What is the correct trend going down groups 1 and 17? A. Melting points increase B. Boiling...
22M.1A.SL.TZ1.8:
Which of the following is the electron configuration of a metallic element?

A. [Ne] 3s² 3p²

B. [Ne] 3s² 3p⁴

C. [Ne] 3s² 3p⁶ 3d³ 4s²

D. [Ne] 3s² 3p⁶ 3d¹⁰ 4s² 4p⁵

Structure 3.1.5—Metallic and non-metallic properties show a continuum. This includes the trend from basic metal oxides through amphoteric to acidic non-metal oxides. Deduce equations for the reactions with water of the oxides of group 1 and group 2 metals, carbon and sulfur.

22M.2.SL.TZ2.3c(i): State the product formed from the reaction of SO3 with water.
22M.2.SL.TZ1.1a(iii): Identify a metal, in the same period as magnesium, that does not form a basic oxide.
22M.2.SL.TZ2.6d(i):
State the product formed from the reaction of SO₃ with water.
21N.1A.SL.TZ0.8: Which combination describes the acid–base nature of aluminium and phosphorus oxides?
19M.2.SL.TZ2.3c:
Suggest why it is surprising that dinitrogen monoxide dissolves in water to give a neutral solution.
19M.1A.SL.TZ2.20:
What is the major reason why the pH of unpolluted rain is less than 7?

A. methane

B. carbon dioxide

C. nitrogen oxides

D. sulfur dioxide
19M.1A.SL.TZ2.25:
What is the major reason why the pH of unpolluted rain is less than 7?

A. methane

B. carbon dioxide

C. nitrogen oxides

D. sulfur dioxide
22M.1A.SL.TZ1.7: Which gases are acidic? I. nitrogen dioxideII. carbon dioxideIII. sulfur dioxide A. I and...
21M.2.SL.TZ2.1e:
Outline how one calcium compound in the lime cycle can reduce a problem caused by acid deposition.
21M.2.SL.TZ1.1e(iii): Suggest why this process might raise environmental concerns.
21M.1A.SL.TZ2.20: Which causes acid deposition? A. SO2 B. SiO2 C. SrO D. CO2
21M.2.SL.TZ1.1d(iii): Suggest why this process might raise environmental concerns.
20N.1A.SL.TZ0.24:
Which of these oxides contribute to acid deposition?

I.   ${SO}_{2}$
II.   ${NO}_{2}$
III.   ${CO}_{2}$

A. I and II only

B. I and III only

C. II and III only

D. I, II and III
20N.1A.SL.TZ0.8:
Which oxide will dissolve in water to give the solution with the lowest pH?

A.   $P_{4} O_{10}$

B.   ${SiO}_{2}$

C.   ${Al}_{2} O_{3}$

D.   $MgO$
22N.2.SL.TZ0.5b:
Write an equation that shows how sulfur dioxide can produce acid rain.
22M.2.SL.TZ2.3c(i): State the product formed from the reaction of SO3 with water.
22M.2.SL.TZ2.c(i): State the product formed from the reaction of SO3 with water.
22M.2.SL.TZ1.1a(iii): Identify a metal, in the same period as magnesium, that does not form a basic oxide.
22M.2.SL.TZ1.a(iii): Identify a metal, in the same period as magnesium, that does not form a basic oxide.
22M.2.SL.TZ2.6d(i):
State the product formed from the reaction of SO₃ with water.
22M.2.SL.TZ2.d(i):
State the product formed from the reaction of SO₃ with water.
21N.1A.SL.TZ0.8: Which combination describes the acid–base nature of aluminium and phosphorus oxides?
19M.2.SL.TZ2.3c:
Suggest why it is surprising that dinitrogen monoxide dissolves in water to give a neutral solution.
19M.2.SL.TZ2.c:
Suggest why it is surprising that dinitrogen monoxide dissolves in water to give a neutral solution.
19M.1A.SL.TZ2.20:
What is the major reason why the pH of unpolluted rain is less than 7?

A. methane

B. carbon dioxide

C. nitrogen oxides

D. sulfur dioxide
19M.1A.SL.TZ2.25:
What is the major reason why the pH of unpolluted rain is less than 7?

A. methane

B. carbon dioxide

C. nitrogen oxides

D. sulfur dioxide
22M.1A.SL.TZ1.7: Which gases are acidic? I. nitrogen dioxideII. carbon dioxideIII. sulfur dioxide A. I and...
21M.2.SL.TZ2.1e:
Outline how one calcium compound in the lime cycle can reduce a problem caused by acid deposition.
21M.2.SL.TZ2.e:
Outline how one calcium compound in the lime cycle can reduce a problem caused by acid deposition.
21M.2.SL.TZ1.1e(iii): Suggest why this process might raise environmental concerns.
21M.2.SL.TZ1.e(iii): Suggest why this process might raise environmental concerns.
21M.1A.SL.TZ2.20: Which causes acid deposition? A. SO2 B. SiO2 C. SrO D. CO2
21M.2.SL.TZ1.1d(iii): Suggest why this process might raise environmental concerns.
21M.2.SL.TZ1.d(iii): Suggest why this process might raise environmental concerns.
20N.1A.SL.TZ0.24:
Which of these oxides contribute to acid deposition?

I.   ${SO}_{2}$
II.   ${NO}_{2}$
III.   ${CO}_{2}$

A. I and II only

B. I and III only

C. II and III only

D. I, II and III
20N.1A.SL.TZ0.8:
Which oxide will dissolve in water to give the solution with the lowest pH?

A.   $P_{4} O_{10}$

B.   ${SiO}_{2}$

C.   ${Al}_{2} O_{3}$

D.   $MgO$
22N.2.SL.TZ0.5b:
Write an equation that shows how sulfur dioxide can produce acid rain.
22N.2.SL.TZ0.b:
Write an equation that shows how sulfur dioxide can produce acid rain.

Structure 3.1.6—The oxidation state is a number assigned to an atom to show the number of electrons transferred in forming a bond. It is the charge that atom would have if the compound were composed of ions. Deduce the oxidation states of an atom in an ion or a compound.

19M.2.SL.TZ2.4e(i):
Suggest why the existence of salts containing an ion with this formula could be predicted. Refer to section 7 of the data booklet.
22M.2.SL.TZ2.5b:
Calculate the oxidation state of sulfur in iron(II) disulfide, FeS₂.
19M.1A.HL.TZ2.8:
What is the oxidation state of the metal ion and charge of the complex ion in [Co(NH₃)₄Cl₂]Cl?
19M.1A.SL.TZ2.21: Which species contains nitrogen with the highest oxidation state? A. NO3− B. NO2− C. NO2 D. N2O
22M.1A.SL.TZ2.11:
What is the name of the compound with formula Ti₃(PO₄)₂?

A. Titanium phosphate

B. Titanium(II) phosphate

C. Titanium(III) phosphate

D. Titanium(IV) phosphate
19N.1B.SL.TZ0.2a(iii): List the three products at the anode from the least to the most oxidized.
21M.1A.SL.TZ2.21: What is the oxidation state of oxygen in H2O2? A. −2 B. −1 C. +1 D. +2
21N.1A.HL.TZ0.8:
Which complex ion contains a central ion with an oxidation state of +3?

A. [PtCl₆]²⁻

B. [Cu(H₂O)₄(OH)₂]

C. [Ni(NH₃)₄(H₂O)₂]²⁺

D. [Co(NH₃)₄Cl₂]⁺
19M.2.SL.TZ2.4e(i):
Suggest why the existence of salts containing an ion with this formula could be predicted. Refer to section 7 of the data booklet.
19M.2.SL.TZ2.e(i):
Suggest why the existence of salts containing an ion with this formula could be predicted. Refer to section 7 of the data booklet.
22M.2.SL.TZ2.5b:
Calculate the oxidation state of sulfur in iron(II) disulfide, FeS₂.
22M.2.SL.TZ2.b:
Calculate the oxidation state of sulfur in iron(II) disulfide, FeS₂.
19M.1A.HL.TZ2.8:
What is the oxidation state of the metal ion and charge of the complex ion in [Co(NH₃)₄Cl₂]Cl?
19M.1A.SL.TZ2.21: Which species contains nitrogen with the highest oxidation state? A. NO3− B. NO2− C. NO2 D. N2O
22M.1A.SL.TZ2.11:
What is the name of the compound with formula Ti₃(PO₄)₂?

A. Titanium phosphate

B. Titanium(II) phosphate

C. Titanium(III) phosphate

D. Titanium(IV) phosphate
19N.1B.SL.TZ0.a(iii): List the three products at the anode from the least to the most oxidized.
21M.1A.SL.TZ2.21: What is the oxidation state of oxygen in H2O2? A. −2 B. −1 C. +1 D. +2
21N.1A.HL.TZ0.8:
Which complex ion contains a central ion with an oxidation state of +3?

A. [PtCl₆]²⁻

B. [Cu(H₂O)₄(OH)₂]

C. [Ni(NH₃)₄(H₂O)₂]²⁺

D. [Co(NH₃)₄Cl₂]⁺

Structure 3.1.7—Discontinuities occur in the trend of increasing first ionization energy across a period. Explain how these discontinuities provide evidence for the existence of energy sublevels.

21M.1A.HL.TZ1.6: The diagram shows the first ionisation energies of consecutive elements in the same period of the...
21M.1A.HL.TZ1.6: The diagram shows the first ionisation energies of consecutive elements in the same period of the...

Structure 3.1.8—Transition elements have incomplete d-sublevels that give them characteristic properties. Recognize properties, including: variable oxidation state, high melting points, magnetic properties, catalytic properties, formation of coloured compounds and formation of complex ions with ligands.

Structure 3.1.9—The formation of variable oxidation states in transition elements can be explained by the fact that their successive ionization energies are close in value. Deduce the electron configurations of ions of the first-row transition elements.

Structure 3.1.10—Transition element complexes are coloured due to the absorption of light when an electron is promoted between the orbitals in the split d-sublevels. The colour absorbed is complementary to the colour observed. Apply the colour wheel to deduce the wavelengths and frequencies of light absorbed and/or observed.