Electron Distribution in Chemical Bonds

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Questions and Answers

What is the oxidation state of sodium in sodium metal?

  • 0 (correct)
  • -1
  • +2
  • +1

What oxidation state is assigned to chlorine in Cl2 gas?

  • 0 (correct)
  • +1
  • -1
  • +2

What is the oxidation state of sulfur in the ion S2−?

  • -2 (correct)
  • +2
  • -1
  • 0

What must the sum of oxidation states equal in a neutral compound?

<p>0 (D)</p> Signup and view all the answers

What is the oxidation number of oxygen in a peroxide (O2^2−)?

<p>-1 (B)</p> Signup and view all the answers

In KMnO4, what is the oxidation state of manganese (Mn)?

<p>+7 (D)</p> Signup and view all the answers

When arranging oxidation states, which element is typically assigned a positive oxidation number first?

<p>Most metallic elements (C)</p> Signup and view all the answers

What is the oxidation state of phosphorus in Na3PO4?

<p>+5 (C)</p> Signup and view all the answers

How are oxidation states of atoms in a polyatomic ion determined?

<p>Must equal the sum of ionic charges (D)</p> Signup and view all the answers

What is the oxidation number of lithium in LiCl?

<p>+1 (B)</p> Signup and view all the answers

What is the purpose of assigning an oxidation state to an atom in a substance?

<p>To track the distribution of electrons between atoms (C)</p> Signup and view all the answers

How do oxidation states differ from ionic charges?

<p>Oxidation states can be assigned without electron transfer, while ionic charges cannot (D)</p> Signup and view all the answers

What oxidation state is assigned to a pure element?

<p>0 (D)</p> Signup and view all the answers

In the compound NaCl, what happens to the electron when sodium forms Na+?

<p>It is transferred from sodium to chlorine (C)</p> Signup and view all the answers

Which of the following correctly represents the oxidation state and ionic charge of Na+?

<p>+1, +1 (B)</p> Signup and view all the answers

How can we track electron distribution in substances without electron transfer?

<p>Through oxidation states assigned to the atoms (A)</p> Signup and view all the answers

What concept is crucial for determining oxidation states based on electron transfer?

<p>Electronegativity differences (D)</p> Signup and view all the answers

Why might it be challenging to identify electron distribution in polar covalent bonds like H2O?

<p>There is no electron transfer between the atoms (B)</p> Signup and view all the answers

Flashcards

Metallic and Non-Metallic Character

The tendency of an atom to lose or gain electrons in chemical bonding.

Oxidation State

A numerical, hypothetical charge assigned to an atom in a substance based on the degree of electron transfer between atoms. It reflects the relative electronegativities of elements.

Ionic Charge

Indicates the actual charge of an ion resulting from the loss or gain of electrons.

Polar Covalent Bond

A type of chemical bond where electrons are shared unequally between two atoms, resulting in a partial positive and partial negative charge on each atom.

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Non-Polar Covalent Bond

A chemical bond where electrons are shared equally between two atoms, resulting in no overall charge imbalance.

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Electronegativity

The ability of an atom to attract electrons in a chemical bond.

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Compound

A substance composed of two or more elements chemically bonded together.

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Oxidation State Assignment

A method for tracking the distribution of electrons in a substance by assigning oxidation states to each atom, regardless of bonding type.

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Oxidation state of pure elements

The oxidation state of an atom in a pure element is always 0 because electrons are shared equally between identical atoms.

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Oxidation state of monatomic ions

The oxidation state of a monatomic ion is equal to the charge of the ion. For example, Cu2+ has an oxidation state of +2.

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Oxidation state in neutral compounds

The sum of the oxidation states of all atoms in a neutral compound must equal zero.

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Oxidation state in polyatomic ions

The sum of the oxidation states of all atoms in a polyatomic ion must equal the overall charge of the ion. For example, the OH- ion has a charge of -1, so the sum of the oxidation states of oxygen and hydrogen must equal -1.

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Typical oxidation states of groups

Group 1 metals typically have a +1 oxidation state, Group 2 metals have a +2 oxidation state, and Group 17 elements have a -1 oxidation state (except when bonded to a more electronegative halogen).

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Oxygen oxidation state

Oxygen typically has an oxidation state of -2, except in peroxides (O22-) where it is -1.

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Hydrogen oxidation state

Hydrogen typically has an oxidation state of +1, except in metallic hydrides (like NaH) where it is -1.

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Order of assigning oxidation states

Assign positive oxidation numbers to the most metallic elements first and negative oxidation numbers to the most non-metallic elements first when determining oxidation states in a compound.

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Solving for oxidation states in complex compounds

Use a mathematical equation and algebra to solve for the oxidation state of an element, especially in compounds with more than two elements.

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Practice makes perfect

Practice identifying oxidation states with different compounds and ions to build your understanding.

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Study Notes

Tracking Electron Distribution in Chemical Bonds

  • Atoms' tendencies to lose or gain electrons dictate their metallic/non-metallic character.
  • Chemical bonds involve electron transfer or distribution.
  • Ionic bonding involves electron transfer. In NaCl, sodium loses an electron to chlorine.
  • Covalent bonds involve electron sharing. In H₂O, electrons are unequally shared.

Oxidation States: A Tool for Electron Tracking

  • Oxidation state (or oxidation number) is a hypothetical charge assigned to an atom in a substance.
  • It reflects the degree of electron transfer between atoms.
  • It's based on relative electronegativities of elements.
  • It's a method to track electron distribution regardless of bond type.
  • Oxidation state is different from ionic charge: ionic charge is an actual charge representing lost or gained electrons.
  • Oxidation state is hypothetical and is a tool to track electron distribution.

Rules for Assigning Oxidation States

  • Pure Element: Oxidation state is 0 (e.g., Na(s), Cl₂(g)). This is because there's no electron transfer within the element itself.
  • Monoatomic Ion: Oxidation state equals the ion's charge (e.g., Cu²⁺ = +2, Cl⁻ = -1).
  • Neutral Compound: Oxidation states sum to zero. (e.g., LiCl: +1 + (-1) = 0).
  • Polyatomic Ion: Oxidation states sum to the ion's charge. (e.g., OH⁻: -2 + 1 = -1).
  • Typical Oxidation States: Certain elements have predictable oxidation states: e.g., Group 1 metals (+1), Group 2 metals (+2), Group 17 elements (-1), Oxygen (-2), and Hydrogen (+1). Exceptions to these rules exist (peroxides, metallic hydrides).

Example Applications

  • Oxidation state determination using mathematical approach to deduce final value.
    • In compounds with multiple elements, assigning assumed oxidation states and setting up equations to find unknowns.
    • Examples include KMnO₄ (Potassium Permanganate) and Na₃PO₄ (Sodium Phosphate) illustrating the process to solve for oxidation numbers of relevant elements.

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