UPCAT Chemistry — Periodic Table, Bonding & Chemical LanguageExam Answer Templates

Marks

1

Topic

Periodic Table

Difficulty

easy

Template Id

T1

Examiner Tip

Mention 'atomic numbers' specifically, not atomic mass

Model Answer

The physical and chemical properties of elements are periodic functions of their atomic numbers.

Question Type

very_short_answer

Answer Structure

• State the complete law definition [1 mark]

Scoring Breakdown

Common Mark Deductions

• Using atomic mass instead of atomic number
• Incomplete statement

Key Phrases To Include

• atomic numbers
• periodic functions
• properties

Marks

2

Topic

Periodic Trends

Difficulty

medium

Template Id

T2

Examiner Tip

Always state both the trend and the reason for full marks

Model Answer

Down a group: Atomic radius increases because additional electron shells are added, increasing the distance between the nucleus and outermost electrons. Across a period: Atomic radius decreases because nuclear charge increases while the number of electron shells remains constant, pulling electrons closer to the nucleus.

Question Type

short_answer

Answer Structure

• Down a group trend with reason [1 mark]
• Across a period trend with reason [1 mark]

Scoring Breakdown

Common Mark Deductions

• Not mentioning the reason
• Confusing the directions

Key Phrases To Include

• increases
• decreases
• electron shells
• nuclear charge

Marks

3

Topic

Chemical Bonding and VSEPR

Difficulty

medium

Template Id

T3

Examiner Tip

Always distinguish between electronic geometry and molecular geometry

Model Answer

Lewis structure: N with 3 single bonds to H atoms and 1 lone pair on N. Electron pairs around central atom: 4 (3 bonding + 1 lone pair) Electronic geometry: Tetrahedral Molecular geometry: Trigonal pyramidal (due to lone pair repulsion)

Question Type

diagram_based

Answer Structure

• Correct Lewis structure [1 mark]
• Count electron pairs correctly [1 mark]
• State correct molecular geometry [1 mark]

Scoring Breakdown

Common Mark Deductions

• Incorrect electron count
• Not considering lone pairs
• Wrong geometry name

Key Phrases To Include

• lone pair
• trigonal pyramidal
• VSEPR
• tetrahedral

Marks

3

Topic

Chemical Nomenclature

Difficulty

easy

Template Id

T4

Examiner Tip

Use Greek prefixes for covalent compounds and remember common acid names

Model Answer

(i) CaCl₂ - Calcium chloride (ii) SO₂ - Sulfur dioxide (iii) HNO₃ - Nitric acid

Question Type

short_answer

Answer Structure

• Correct name for ionic compound [1 mark]
• Correct name for covalent compound with prefix [1 mark]
• Correct name for oxyacid [1 mark]

Scoring Breakdown

Common Mark Deductions

• Missing prefixes in covalent compounds
• Incorrect acid names

Key Phrases To Include

• calcium chloride
• sulfur dioxide
• nitric acid

Marks

3

Topic

Chemical Bonding Types

Difficulty

medium

Template Id

T5

Examiner Tip

Always provide specific examples for each bond type

Model Answer

Ionic Bond: Formed by complete transfer of electrons from metal to non-metal, creating charged ions. Example: NaCl (Na⁺ and Cl⁻) Covalent Bond: Formed by sharing of electrons between non-metals. Example: H₂O (sharing between H and O atoms) Ionic bonds occur between metals and non-metals, while covalent bonds occur between non-metals only.

Question Type

short_answer

Answer Structure

• Define ionic bond with example [1 mark]
• Define covalent bond with example [1 mark]
• State key difference [1 mark]

Scoring Breakdown

Common Mark Deductions

• No examples given
• Incorrect examples
• Unclear definitions

Key Phrases To Include

• electron transfer
• electron sharing
• metal to non-metal
• non-metal to non-metal

Marks

3

Topic

Chemical Formulas

Difficulty

medium

Template Id

T6

Examiner Tip

Always show all calculation steps clearly

Model Answer

Given: C = 40%, H = 6.7%, O = 53.3% Step 1: Convert to moles C: 40/12 = 3.33 mol H: 6.7/1 = 6.7 mol O: 53.3/16 = 3.33 mol Step 2: Divide by smallest C: 3.33/3.33 = 1 H: 6.7/3.33 = 2 O: 3.33/3.33 = 1 Empirical formula: CH₂O

Question Type

numerical

Answer Structure

• Convert percentages to moles [1 mark]
• Find simplest ratio [1 mark]
• Write empirical formula [1 mark]

Scoring Breakdown

Common Mark Deductions

• Arithmetic errors
• Not showing working
• Wrong atomic masses

Key Phrases To Include

• moles
• atomic mass
• simplest ratio
• empirical formula

Marks

2

Topic

Periodic Table - Noble Gases

Difficulty

easy

Template Id

T7

Examiner Tip

Connect electron configuration to chemical behavior

Model Answer

Noble gases have completely filled outermost electron shells (octet configuration), making them very stable. They do not need to gain, lose, or share electrons to achieve stability, hence they are generally unreactive.

Question Type

short_answer

Answer Structure

• State that they have complete outer shells [1 mark]
• Explain why this makes them unreactive [1 mark]

Scoring Breakdown

Common Mark Deductions

• Only stating the fact without explanation
• Incorrect electron configuration

Key Phrases To Include

• complete outer shell
• octet configuration
• stable
• unreactive

Marks

5

Topic

Intermolecular Forces

Difficulty

hard

Template Id

T8

Examiner Tip

Always relate IMFA strength to electronegativity differences

Model Answer

Order: CH₄ < NH₃ < H₂O < HF Justification: CH₄ (methane): Non-polar molecule, only London dispersion forces (weakest) NH₃ (ammonia): Polar molecule with hydrogen bonding (N-H bonds), stronger than dispersion H₂O (water): Polar molecule with hydrogen bonding (O-H bonds), oxygen more electronegative than nitrogen HF (hydrogen fluoride): Polar molecule with strongest hydrogen bonding (F-H bonds), fluorine most electronegative Strength order: London dispersion < Dipole-dipole < Hydrogen bonding (N-H) < Hydrogen bonding (O-H) < Hydrogen bonding (F-H)

Question Type

long_answer

Answer Structure

• Write correct order [1 mark]
• Identify IMF type for CH₄ [1 mark]
• Identify IMF type for NH₃ [1 mark]
• Identify IMF type for H₂O [1 mark]
• Identify IMF type for HF with proper reasoning [1 mark]

Scoring Breakdown

Common Mark Deductions

• Wrong order
• Not mentioning electronegativity
• Confusing IMFA types

Key Phrases To Include

• London dispersion
• hydrogen bonding
• electronegativity
• polar
• non-polar

Marks

1

Topic

Chemical Formulas

Difficulty

easy

Template Id

T9

Examiner Tip

Use the criss-cross method and remember parentheses for polyatomic ions

Model Answer

Al₂(SO₄)₃

Question Type

very_short_answer

Answer Structure

• Correct formula with proper subscripts [1 mark]

Scoring Breakdown

Common Mark Deductions

• Incorrect subscripts
• Missing parentheses for polyatomic ion

Key Phrases To Include

• Al₂(SO₄)₃

Marks

3

Topic

Periodic Trends

Difficulty

medium

Template Id

T10

Examiner Tip

Always explain the underlying cause of the trend

Model Answer

Electronegativity is the ability of an atom to attract shared electrons in a chemical bond. Trend across period: Increases from left to right due to increasing nuclear charge. Trend down group: Decreases from top to bottom due to increasing atomic size and electron shielding.

Question Type

short_answer

Answer Structure

• Define electronegativity [1 mark]
• Explain trend across period [1 mark]
• Explain trend down group [1 mark]

Scoring Breakdown

Common Mark Deductions

• Incomplete definition
• Wrong trends
• No reasoning given

Key Phrases To Include

• attract electrons
• increases
• decreases
• nuclear charge
• atomic size

Marks

2

Topic

Chemical Formulas

Difficulty

easy

Template Id

T11

Examiner Tip

Use glucose as a clear example - it's commonly known

Model Answer

Molecular formula shows the actual number of each type of atom in a molecule, while empirical formula shows the simplest whole number ratio of atoms. Example: Glucose has molecular formula C₆H₁₂O₆ and empirical formula CH₂O.

Question Type

short_answer

Answer Structure

• Define both formulas clearly [1 mark]
• Give a correct example [1 mark]

Scoring Breakdown

Common Mark Deductions

• Unclear definitions
• Incorrect example

Key Phrases To Include

• actual number
• simplest ratio
• whole number

Marks

3

Topic

Ionic Bonding

Difficulty

medium

Template Id

T12

Examiner Tip

Always show the electron configurations before and after transfer

Model Answer

Na (2,8,1) loses 1 electron to become Na⁺ (2,8) achieving noble gas configuration of neon. Cl (2,8,7) gains 1 electron to become Cl⁻ (2,8,8) achieving noble gas configuration of argon. Electrostatic attraction between Na⁺ and Cl⁻ forms the ionic bond in NaCl.

Question Type

short_answer

Answer Structure

• Show Na losing electron with configuration [1 mark]
• Show Cl gaining electron with configuration [1 mark]
• Explain electrostatic attraction [1 mark]

Scoring Breakdown

Common Mark Deductions

• Wrong electron configurations
• Not showing the transfer clearly

Key Phrases To Include

• electron transfer
• noble gas configuration
• electrostatic attraction

Marks

2

Topic

Ionic Compounds Properties

Difficulty

easy

Template Id

T13

Examiner Tip

Focus on distinctive properties that differ from covalent compounds

Model Answer

1. High melting and boiling points 2. Conduct electricity when molten or in solution 3. Soluble in polar solvents like water 4. Form crystalline structures

Question Type

short_answer

Answer Structure

• List any two properties correctly [1 mark]
• List any two additional properties correctly [1 mark]

Scoring Breakdown

Common Mark Deductions

• Listing properties of covalent compounds instead
• Vague descriptions

Key Phrases To Include

• high melting point
• conduct electricity
• soluble in water
• crystalline

Marks

3

Topic

Molecular Geometry

Difficulty

medium

Template Id

T14

Examiner Tip

Remember CO₂ has double bonds, not single bonds

Model Answer

Lewis structure: O=C=O (carbon in center with double bonds to each oxygen) Electron pairs around central carbon: 2 (both are bonding pairs, no lone pairs) According to VSEPR theory, 2 electron pairs arrange themselves as far apart as possible, giving a linear geometry with bond angle 180°.

Question Type

diagram_based

Answer Structure

• Draw correct Lewis structure [1 mark]
• Count electron pairs correctly [1 mark]
• Explain linear geometry using VSEPR [1 mark]

Scoring Breakdown

Common Mark Deductions

• Single bonds instead of double
• Wrong geometry
• No VSEPR reference

Key Phrases To Include

• double bonds
• linear
• VSEPR
• 180 degrees

Marks

5

Topic

Chemical Bonding Comparison

Difficulty

hard

Template Id

T15

Examiner Tip

Distinguish between network and molecular covalent compounds

Model Answer

Metallic Bonds: - Conductivity: Excellent electrical and thermal conductors due to mobile electrons - Melting point: Generally high due to strong metallic bonding Ionic Bonds: - Conductivity: Conduct electricity only when molten or in solution (mobile ions) - Melting point: High due to strong electrostatic forces between ions Covalent Bonds: - Conductivity: Generally poor conductors (no mobile charges) - Melting point: Variable - network covalent (high), molecular covalent (low) Order of conductivity: Metallic > Ionic (when molten) > Covalent

Question Type

long_answer

Answer Structure

• Describe metallic bond properties [1 mark]
• Describe ionic bond properties [1 mark]
• Describe covalent bond properties [1 mark]
• Compare conductivity [1 mark]
• Compare melting points [1 mark]

Scoring Breakdown

Common Mark Deductions

• Not distinguishing types of covalent compounds
• Incorrect conductivity explanations

Key Phrases To Include

• mobile electrons
• electrostatic forces
• network covalent
• molecular covalent