Chemistry Chapter 1: The Language of Chemistry

Symbols in Chemistry

• Represent elements
• 118 elements, each with a unique symbol (e.g., S for Sulfur)
• Initially diagrammatic, switched to letters by Berzelius
• Often based on Latin names (e.g., Ag for Silver from 'Argentine')

Valency

• Combining capacity of an atom or radical
• Examples:
  • Chlorine forms HCl, valency = 1
  • Oxygen forms H2O, valency = 2
  • Nitrogen in ammonia (NH3), valency = 3
• Metals and hydrogen have positive valency; non-metals have negative valency
• Valency also indicates electrons lost/gained/shared
• Transition elements can have variable valency (e.g., Cu^+, Cu^2+)

Radicals

• Atom/group behaving as single unit with valency
• Positive radical: Ammonium (NH4^+)
• Negative radical: Hydroxide (OH^-)

Chemical Formula

• Representation of molecules using symbols
• Example: Ammonium carbonate (NH4)2CO3
• Crisscross method to form chemical formulae
• Differentiate between compound types (e.g., sulfate vs. sulfite)

Compounds

• Pure substances from two/more elements combined chemically
• Fixed ratio; properties differ from constituent elements (e.g., water)

Chemical Equations

• Shorthand for chemical changes
• Example: NH4OH + HCl → NH4Cl + H2O
• Must be balanced (law of conservation of matter)
• Indicate states: solid (S), gas (G), liquid (L), aqueous (AQ)

Balancing Equations

• Equal number of atoms for each element on both sides
• Complies with law of conservation of matter

Relative Atomic and Molecular Mass

• Atomic mass: number of protons + neutrons
• Relative atomic mass: compared to 1/12 mass of carbon-12 atom
• Molecular mass: sum of atomic masses in a molecule (e.g., H2O = 18 amu)

• Note: Mass numbers can be decimals due to isotopes, e.g., chlorine (35.5)