Chemistry • Year 11 • Module 1 • Lesson 18
Periodic Trends: Electronegativity and Reactivity
Anchor the core vocabulary, Pauling scale values, and the two key trends before tackling more complex questions.
1. Term–definition match
The definitions below are shuffled. In the right-hand column write the matching term from this list: electronegativity, Pauling scale, polar covalent bond, non-polar covalent bond, ionic bond, effective nuclear charge (Zeff), metallic reactivity, non-metallic reactivity, bond polarity, electronegativity difference (|Δχ|). 10 marks (1 each)
| # | Definition | Matching term |
|---|---|---|
| 1.1 | A dimensionless measure of an atom’s tendency to attract bonding electrons toward itself in a covalent bond. | |
| 1.2 | The relative scale (0–4) used to assign numerical electronegativity values, with fluorine set at 4.0. | |
| 1.3 | A covalent bond in which bonding electrons are unequally shared, creating partial charges (δ+ and δ−) on the bonded atoms. | |
| 1.4 | A covalent bond in which bonding electrons are essentially equally shared; |Δχ| < 0.4. | |
| 1.5 | A bond formed by the effective transfer of one or more electrons from a metal to a non-metal; |Δχ| ≥ 1.7. | |
| 1.6 | The net positive charge experienced by a valence electron after accounting for the shielding effect of inner electrons. | |
| 1.7 | The tendency of a metal to lose electrons and undergo oxidation in chemical reactions; increases down a group. | |
| 1.8 | The tendency of a non-metal to gain electrons and undergo reduction in chemical reactions; decreases down a group. | |
| 1.9 | The unequal distribution of electron density in a bond between atoms of different electronegativity, producing partial charges. | |
| 1.10 | The absolute difference in Pauling electronegativity values between two bonded atoms, used to classify bond type. |
2. True or false — with correction
Circle T or F for each statement. If the statement is false, write the corrected version on the line below it. 12 marks (1 T/F + 1 correction each)
2.1 Electronegativity increases from left to right across a period because atomic radius decreases and effective nuclear charge increases. T / F
2.2 Electronegativity increases going down a group because more electron shells are added, increasing the nuclear pull on bonding electrons. T / F
2.3 Fluorine (F) is the most electronegative element with a Pauling value of 4.0. T / F
2.4 Metal reactivity decreases going down a group because the ionisation energy decreases. T / F
2.5 Non-metal reactivity decreases going down a group because the atomic radius increases, making it harder for the nucleus to attract an incoming electron. T / F
2.6 Noble gases are assigned electronegativity values because they can form bonds under extreme conditions. T / F
3. Fill-in-the-blank paragraph
Use the word bank to complete the passage. Each word is used once. 9 marks (1 per blank)
Word bank:
decreases · electronegativity · equal · gain · ionic · lose · period · polar covalent · shielding
___________ is the ability of an atom in a bond to attract shared electrons toward itself. Across a ___________, electronegativity increases from left to right because Zeff increases while inner-shell ___________ remains approximately constant. Down a group, electronegativity ___________ as extra electron shells increase the distance between the nucleus and bonding electrons. When two identical atoms bond, the electrons are shared ___________, producing a non-polar covalent bond. When atoms of different electronegativity bond and |Δχ| is between 0.4 and 1.7, the bond is ___________. When |Δχ| ≥ 1.7, the bond is classified as ___________. Metals react by ___________ electrons, while non-metals react by ___________ electrons.
4. Function recall
Answer each question in 1–2 sentences using precise terms from the lesson. 8 marks (2 each)
4.1 Using the concept of effective nuclear charge, explain why electronegativity increases across Period 2 from Li to F.
4.2 Explain why the metallic reactivity of Group 1 elements increases going down the group, while non-metallic reactivity of Group 17 elements decreases going down the group. Reference the same underlying structural reason.
4.3 State the three |Δχ| ranges and the bond type associated with each range.
4.4 Why are noble gases not assigned electronegativity values on the Pauling scale?
5. Pauling electronegativity values — recall and rank
The table below lists ten elements. Fill in the missing Pauling electronegativity values (use the lesson table) and then answer the questions below. 8 marks
| Element | Symbol | Group | Period | Pauling χ value |
|---|---|---|---|---|
| Fluorine | F | 17 | 2 | |
| Oxygen | O | 16 | 2 | |
| Nitrogen | N | 15 | 2 | |
| Chlorine | Cl | 17 | 3 | |
| Carbon | C | 14 | 2 | |
| Hydrogen | H | 1 | 1 | |
| Sodium | Na | 1 | 3 | |
| Magnesium | Mg | 2 | 3 | |
| Silicon | Si | 14 | 3 | |
| Phosphorus | P | 15 | 3 |
5.1 List the ten elements above in order of decreasing electronegativity (highest first). (3 marks)
5.2 Using only periodic table position (not the values you filled in), explain why F has a higher electronegativity than Cl, even though both are in Group 17. (2 marks)
Q1 — Term–definition match
1.1 electronegativity • 1.2 Pauling scale • 1.3 polar covalent bond • 1.4 non-polar covalent bond • 1.5 ionic bond • 1.6 effective nuclear charge (Zeff) • 1.7 metallic reactivity • 1.8 non-metallic reactivity • 1.9 bond polarity • 1.10 electronegativity difference (|Δχ|).
Q2 — True / false with correction
2.1 True. Across a period, atomic radius decreases and Zeff increases, pulling bonding electrons more strongly.
2.2 False. Electronegativity decreases going down a group. Extra shells increase atomic radius and shielding, so the nucleus attracts bonding electrons less strongly — not more.
2.3 True. Fluorine has the highest Pauling electronegativity of all elements: χ = 4.0.
2.4 False. Metal reactivity increases going down a group because ionisation energy decreases (easier to lose the valence electron), not the other way around.
2.5 True. A larger atomic radius means the valence shell is further from the nucleus and more shielded, weakening the nucleus’s pull on an incoming electron.
2.6 False. Noble gases are generally not assigned Pauling electronegativity values because they rarely form the covalent bonds on which the Pauling scale is based.
Q3 — Cloze paragraph
In order: Electronegativity / period / shielding / decreases / equal / polar covalent / ionic / lose / gain.
Q4.1 — Electronegativity across Period 2
Across Period 2, each successive element has one more proton but electrons are added to the same (second) shell, providing roughly the same shielding. Therefore Zeff increases from Li to F. Greater Zeff means a stronger pull on bonding electrons, increasing electronegativity from Li (χ = 1.0) to F (χ = 4.0).
Q4.2 — Opposite reactivity trends for metals vs non-metals
The underlying reason is the same: going down a group, atomic radius increases and shielding increases, so the valence electrons are held less tightly. For metals (which react by losing electrons), this means it is easier to lose a valence electron → reactivity increases. For non-metals (which react by gaining electrons), the same larger radius means the nucleus attracts an incoming electron more weakly → reactivity decreases.
Q4.3 — |Δχ| ranges and bond types
|Δχ| < 0.4 → non-polar covalent. 0.4 ≤ |Δχ| < 1.7 → polar covalent. |Δχ| ≥ 1.7 → ionic. (These are approximate thresholds — bond character is a continuum.)
Q4.4 — Noble gases not assigned χ values
The Pauling scale is derived from bond energies in covalent molecules. Noble gases have full valence shells and do not normally form covalent bonds, so there is no bonding-electron data on which to base a Pauling value.
Q5 — Pauling values and ranking
Values: F = 4.0 • O = 3.4 • N = 3.0 • Cl = 3.2 • C = 2.6 • H = 2.2 • Na = 0.9 • Mg = 1.3 • Si = 1.9 • P = 2.2.
5.1 Decreasing order: F (4.0) > O (3.4) > Cl (3.2) > N (3.0) > C (2.6) > H (2.2) = P (2.2) > Si (1.9) > Mg (1.3) > Na (0.9). (H and P share the same value; accept either order for these two.)
5.2 F vs Cl: Both are in Group 17, so they have similar numbers of valence electrons. However, F is in Period 2 and Cl is in Period 3. F has a smaller atomic radius (fewer electron shells) and less inner-shell shielding, so its nucleus exerts a stronger pull on bonding electrons → higher electronegativity.