Exam studying

1. Atomic Structure

Bohr vs. Quantum Model

• Bohr: Electrons orbit in fixed shells ($E_n=-\frac{13.6}{n^2}\text{ eV}$).
• Quantum: Electrons in orbitals ($\psi$), defined by quantum numbers:
  • $n$ (shell), $l$ (subshell), $m_l$ (orbital), $m_s$ (spin).

Isotopes

• Notation: ${}_Z^A\text{X}$ (e.g., ${}_{17}^{35}\text{Cl}$).
• Atomic mass: Weighted average of isotopes.

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2. Periodic Trends

Trend	Direction	Example
Atomic Radius	$\downarrow$ group	Li (152 pm) > Na (186 pm)
Ionization Energy	$\to$ period	N (14.5 eV) > O (13.6 eV)
Electronegativity	$\to$ period	F (4.0) > O (3.5)

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3. Chemical Bonding

Ionic vs. Covalent

Property	Ionic (NaCl)	Covalent (H₂O)
Bond Type	Electron transfer	Electron sharing
Melting Point	High (>800°C)	Low (0°C for H₂O)
Conductivity	Only when molten	Never (unless polar)

Hybridization

• $s{p}^3$: Tetrahedral (CH₄).
• $s{p}^2$: Trigonal planar (C₂H₄).
• $sp$: Linear (CO₂).

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4. Stoichiometry & Solutions

Key Formulas

• Moles: $n=\frac{m}{M}\text{(e.g., }10\text{g NaOH }\to \frac{10}{40}=0.25\text{mol)}$
• Molarity: $C=\frac{n}{V}\text{(e.g., }0.5\text{mol in 2L }\to 0.25\text{M)}$
• Dilution: $C_1{V}_1=C_2{V}_2$

Solubility Curve Example

KNO₃ Solubility:  
60°C: 110g/100g H₂O  
20°C: 30g/100g H₂O  
Cooling from 60°C → 20°C crystallizes 80g - 30g = 50g.

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5. Acids & Bases

Theories Compared

Theory	Acid Definition	Base Definition
Arrhenius	Produces H⁺	Produces OH⁻
Brønsted-Lowry	Proton donor (${\text{H}}^{+}$)	Proton acceptor

pH/pOH Calculations

$\text{pH}=-\log [{\text{H}}^{+}]\text{(e.g., }[{\text{H}}^{+}]=1\times 10^{-3}\to \text{pH}=3)$
$\text{pOH}=14-\text{pH}$

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6. Gas Laws

Law	Formula	Example
Boyle’s	$P_1{V}_1=P_2{V}_2$	Halve volume → double pressure
Charles’	$\frac{V_1}{T_1}=\frac{V_2}{T_2}$	Heat gas from 25°C→50°C → volume ↑ ~8%
Ideal Gas	$PV=nRT$	$R=0.0821\frac{\text{Lcdotpatm}}{\text{molcdotpK}}$

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7. Intermolecular Forces (IMFs)

Hierarchy of Strength

1. Hydrogen bonding (H─O/N/F): $\Delta H\approx 20\text{ kJ/mol}$.
2. Dipole-dipole (polar molecules): $\Delta H\approx 5\text{ kJ/mol}$.
3. London dispersion (all molecules): $\Delta H\approx 1\text{ kJ/mol}$.

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8. Organic Chemistry Basics

Functional Groups

• Alcohol: R─OH (e.g., CH₃CH₂OH).
• Carboxylic Acid: R─COOH (e.g., CH₃COOH).
• Amine: R─NH₂ (e.g., CH₃NH₂).

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9. Thermodynamics

Enthalpy Change

• $\Delta H=H_{\text{products}}-H_{\text{reactants}}$
• Exothermic: $\Delta H<0$ (releases heat).
• Endothermic: $\Delta H>0$ (absorbs heat).

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10. Reaction Types

Single vs. Double Displacement

• Single: $A+BC\to AC+B$ (e.g., Zn + CuSO₄ → ZnSO₄ + Cu).
• Double: $AB+CD\to AD+CB$ (e.g., NaCl + AgNO₃ → AgCl + NaNO₃).

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Study Checklist

• Balance 5 chemical equations.
• Calculate molarity for 3 solutions.
• Predict polarity of CO₂, NH₃, CH₄.
• Solve a limiting reagent problem.