Chemistry Notation

\usepackage{chemfig}         % Molecular structures
\usepackage{mhchem}          % Chemical formulas and equations
\usepackage{chemmacros}      % Chemistry macros
\usepackage{siunitx}         % SI units
\usepackage{chemformula}     % Alternative to mhchem
\usepackage{mol2chemfig}     % Convert SMILES to chemfig

% Simple molecules
\ce{H2O}        % Water
\ce{CO2}        % Carbon dioxide
\ce{H2SO4}      % Sulfuric acid
\ce{Ca(OH)2}    % Calcium hydroxide

% Ions
\ce{Na+}        % Sodium ion
\ce{SO4^2-}     % Sulfate ion
\ce{NH4+}       % Ammonium ion

% Isotopes
\ce{^{14}C}     % Carbon-14
\ce{^{235}U}    % Uranium-235

% Physical states
\ce{H2O(l)}     % Liquid water
\ce{CO2(g)}     % Gaseous CO2
\ce{NaCl(s)}    % Solid salt
\ce{Na+(aq)}    % Aqueous sodium ion

% Crystal structures
\ce{CaCO3.H2O}  % Hydrate
\ce{Fe^{II}Fe^{III}2O4}  % Mixed oxidation states

% Simple reaction
\ce{2H2 + O2 -> 2H2O}

% With conditions
\ce{N2 + 3H2 ->[\text{Fe cat.}][450°C, 200 atm] 2NH3}

% Equilibrium
\ce{N2O4 <=> 2NO2}

% With heat
\ce{CaCO3 ->[\Delta] CaO + CO2}

% Precipitation
\ce{AgNO3(aq) + NaCl(aq) -> AgCl v + NaNO3(aq)}

% Multi-step reactions
\begin{align}
\ce{CH4 + Cl2 &->[\text{UV}] CH3Cl + HCl}\\
\ce{CH3Cl + Cl2 &->[\text{UV}] CH2Cl2 + HCl}
\end{align}

% Organic reactions
\ce{R-OH + R'-COOH <=>[H+] R'-COO-R + H2O}

% Redox reactions
\ce{MnO4- + 8H+ + 5e- -> Mn^2+ + 4H2O}

% Methane
\chemfig{C(-[2]H)(-[4]H)(-[6]H)-H}

% Ethanol
\chemfig{H-C(-[2]H)(-[6]H)-C(-[2]H)(-[6]H)-OH}

% Benzene
\chemfig{*6(=-=-=-)}

% Cyclohexane (chair conformation)
\chemfig{*6(---(-[,,,,line width=2pt])---)}

% Glucose
\chemfig{
  HO-[2,0.5,2]?<[7,0.7](-[2,0.5]OH)-[,,,,line width=2pt]
  (-[6,0.5]OH)>[1,0.7](-[6,0.5]OH)-[3,0.7]
  (-[4,0.5]OH)-[1,0.7]O-[7,0.7]?
}

% Aspirin
\chemfig{
  *6(=-*6(-(=O)-O-(-=[:30]O)-CH_3)=-=-)
}

% DNA base pairing
\chemfig{
  N**6(--N--C(=[::60]O)--*5(-N=-N(-H)-))
  @{a1}.|[,3.0]|@{a2}.
  N**6(-C(-H_3)-C(=[::60]O)-N(-H)--*5(=N--N=))
}
\chemmove{\draw[dashed] (a1) -- (a2);}

% Nucleophilic substitution
\schemestart
\chemfig{R-X} + \chemfig{\charge{90=\|}{Nu}}
\arrow{->[$S_N2$]}
\chemfig{R-Nu} + \chemfig{X^-}
\schemestop

% Elimination reaction
\schemestart
\chemfig{H-C(-[2]H)(-[6]H)-C(-[2]H)(-[6]X)-H}
\arrow{->[$E2$][-HX]}
\chemfig{H-C(-[2]H)=C(-[6]H)-H}
\schemestop

\chemfig{
  @{a1}\charge{45=\|}{O}-H@{a2}
  \+ R-@{b1}\charge{180=\|}{Br}@{b2}
}
\chemmove{
  \draw[->] (a1) .. controls +(45:5mm) and +(135:5mm) .. (b1);
  \draw[->] (b1) .. controls +(0:5mm) and +(0:5mm) .. (b2);
}

% Using TikZ for simple diagrams
\begin{tikzpicture}
  % Round bottom flask
  \draw (0,0) circle (1cm);
  \draw (-0.3,1) -- (-0.3,2);
  \draw (0.3,1) -- (0.3,2);
  
  % Beaker
  \draw (3,0) -- (3,2) -- (4,2) -- (4,0);
  \draw (3,0) arc (180:360:0.5cm);
\end{tikzpicture}

\begin{table}[h]
\centering
\begin{tabular}{|c|c|c|c|}
\hline
\textbf{Symbol} & \textbf{Name} & \textbf{Number} & \textbf{Mass} \\
\hline
H & Hydrogen & 1 & 1.008 \\
He & Helium & 2 & 4.003 \\
Li & Lithium & 3 & 6.941 \\
Be & Beryllium & 4 & 9.012 \\
\hline
\end{tabular}
\caption{First four elements}
\end{table}

% Using siunitx for proper formatting
\begin{table}[h]
\centering
\begin{tabular}{l S[table-format=3.1] S[table-format=3.1]}
\toprule
Compound & {$\Delta H_f°$ (\si{kJ/mol})} & {$S°$ (\si{J/(mol.K)})} \\
\midrule
\ce{H2O(l)} & -285.8 & 69.9 \\
\ce{CO2(g)} & -393.5 & 213.8 \\
\ce{O2(g)} & 0.0 & 205.0 \\
\bottomrule
\end{tabular}
\end{table}

% Basic units
\SI{25.0}{°C}                    % Temperature
\SI{101.325}{kPa}                % Pressure
\SI{2.5e-3}{mol/L}               % Concentration
\SI{98.5}{\percent}              % Percentage

% Complex units
\SI{8.314}{J/(mol.K)}            % Gas constant
\SI{6.022e23}{mol^{-1}}          % Avogadro's number

% Ranges
\SIrange{20}{25}{°C}
\SIrange{1}{5}{mL}

% Using chemformula package
\ch{H2O}                         % Water
\ch{H+ + OH- <=> H2O}            % Equilibrium
\ch{CO2 + H2O -> H2CO3}          % Reaction

% With stoichiometry
\ch{!( 2 H2 + O2 -> 2 H2O )}

% Oxidation states
\ch{Fe^{III}Cl3}

% Chemical shifts
$\delta$ \SI{7.25}{ppm} (s, 5H, Ph)
$\delta$ \SI{3.65}{ppm} (q, $J = \SI{7.1}{Hz}$, 2H, \ce{CH2})

% Coupling constants
$^3J_\text{HH} = \SI{7.5}{Hz}$
$^1J_\text{CH} = \SI{125}{Hz}$

% Wavenumbers
\SI{3500}{cm^{-1}} (O--H stretch)
\SI{1715}{cm^{-1}} (C=O stretch)
\SI{2950}{cm^{-1}} (C--H stretch)

% Peak descriptions
$\tilde{\nu}$ = \SI{1650}{cm^{-1}} (s, br)