Explaining Reactivity
Section: 9. Metals | Syllabus: Cambridge AS Level Physics 9702
Why Are Metals Reactive? The reactivity of a metal is determined by how easily it loses electrons to form positive ions (cations). Understanding this helps explain why some metals are more reactive than others.
Metal Reactivity The tendency of a metal atom to lose its outer shell electrons and form a positive ion. The more easily a metal loses electrons, the more reactive it is. Metals React by Losing Electrons When metals react, they always lose electrons from their outer shell: General process: Metal atom → Metal ion + electrons M → M n+ + n e - Examples: Metal Electronic Configuration Ion Formation Equation Sodium 2,8,1 Loses 1 electron Na → Na⁺ + e⁻ Magnesium 2,8,2 Loses 2 electrons Mg → Mg²⁺ + 2e⁻ Aluminium 2,8,3 Loses 3 electrons Al → Al³⁺ + 3e⁻ Key Concept The easier it is for a metal to lose electrons, the more reactive it is.
Reactive metals lose electrons readily, while unreactive metals hold onto their electrons more strongly. Factors Affecting Reactivity 1. Number of Electron Shells (Shielding) The more electron shells an atom has, the easier it is to lose outer electrons: Inner electron shells shield (block) the attraction between the nucleus and outer electrons More shells = more shielding = weaker attraction to nucleus Outer electrons are easier to remove when there is more shielding Interactive Diagram Side-by-side comparison of sodium (2,8,1) and potassium (2,8,8,1) atomic structure.
Show concentric circles representing electron shells with electrons as dots. For sodium, show 2 inner shells shielding the outer electron. For potassium, show 3 inner shells providing more shielding. Use arrows from the nucleus labeled "attraction" getting weaker as they pass through more shells.
Include a visual representation of shielding effect with the inner electrons blocking/reducing the nuclear attraction. Add annotation: "Potassium is more reactive because its outer electron is further from nucleus and more shielded." 2.
Distance from the Nucleus The further an electron is from the nucleus, the weaker the electrostatic attraction Atoms with more shells have outer electrons further away Distant electrons are easier to remove 3.
Nuclear Charge More protons in the nucleus = stronger positive charge Stronger nuclear charge = stronger attraction to electrons However, this effect is usually smaller than shielding and distance effects Explaining Reactivity Trends in Group 1 (Alkali Metals) Metal Electronic Structure Number of Shells Relative Reactivity Lithium (Li) 2,1 2 Least reactive ↑ Sodium (Na) 2,8,1 3 More reactive ↑ Potassium (K) 2,8,8,1 4 Most reactive ↑ Explanation: Why Reactivity Increases Down Group 1 All Group 1 metals have 1 electron in their outer shell , so they all want to lose that one electron.
Going down the group: More electron shells are added Outer electron gets further from the nucleus More shielding from inner electrons Weaker attraction between nucleus and outer electron Easier to lose the outer electron = More reactive Example Comparison: Sodium vs Potassium Factor Sodium (Na) Potassium (K) Electron shells 3 shells (2,8,1) 4 shells (2,8,8,1) Shielding 2 inner shells shield outer electron 3 inner shells shield outer electron (more shielding) Distance Outer electron closer to nucleus Outer electron further from nucleus Ease of losing electron Moderate Very easy (less attraction) Reactivity Reactive More reactive Explaining Reactivity Trends in Group 2 (Alkaline Earth Metals) Metal Electronic Structure Number of Shells Relative Reactivity Magnesium (Mg) 2,8,2 3 Less reactive Calcium (Ca) 2,8,8,2 4 More reactive Explanation: Same Pattern as Group 1 All Group 2 metals have 2 electrons in their outer shell , so they all want to lose those 2 electrons.
Going down the group: The same trend applies - more shells mean more shielding and greater distance from nucleus, making it easier to lose electrons. Therefore, calcium is more reactive than magnesium .
Comparing Across Groups: Why Is Sodium More Reactive Than Magnesium? Factor Sodium (Na) Magnesium (Mg) Electronic structure 2,8,1 2,8,2 Number of shells 3 3 (same) Protons (nuclear charge) 11 12 (stronger attraction) Electrons to lose 1 electron 2 electrons First ionisation energy Lower (easier to remove) Higher (harder to remove) Explanation: Why Sodium Is More Reactive Two main reasons: Sodium only needs to lose 1 electron to achieve a stable electronic structure (like neon), while magnesium needs to lose 2 electrons.
Losing one electron is easier than losing two. Magnesium has a higher nuclear charge (12 protons vs 11 protons) with the same number of shells. This means stronger attraction to its outer electrons, making them harder to remove.
Result: Sodium is more reactive than magnesium, even though they're in the same period. Why Are Noble Metals (Cu, Ag, Au) Unreactive? Copper, silver, and gold are at the bottom of the reactivity series and are very unreactive.
This is because: They hold onto their outer electrons very strongly High nu…
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