Ancient Indian and Greek philosophers contemplated the nature of matter, surmising its unseen forms and divisibility.
Around 500 BC, Indian philosopher Maharishi Kanad proposed that continuously dividing matter leads to infinitesimal particles called "Parmanu".
Greek philosophers Democritus and Leucippus suggested that repeated division yields indivisible particles known as "atoms."
Empirical validation emerged only in the eighteenth century.
By the late 18th century, chemists differentiated between elements and compounds.
Antoine Lavoisier established key principles of chemical science, particularly the Laws of Chemical Combination:
Mass remains constant in a chemical reaction; it is neither created nor destroyed.
Demonstrated through an experiment with solutions like copper sulfate and sodium carbonate.
Compounds consist of elements in fixed mass ratios (e.g., water: 1:8 mass ratio of hydrogen and oxygen).
John Dalton introduced his atomic theory in 1808, merging philosophical insights with empirical data:
All matter comprises atoms.
Atoms are indivisible during chemical processes.
Atoms of an element are identical in mass and properties.
Atoms combine in simple whole-number ratios to form compounds.
The number and types of atoms in a compound remain consistent.
Atoms are incredibly minute, measured in nanometres (1 nm = 10^-9 m).
Symbols represent elements, standardized by the International Union of Pure and Applied Chemistry (IUPAC); e.g., H for hydrogen and Na for sodium (Latin name: natrium).
Introduced by Dalton; based on the carbon-12 isotope, establishing the atomic mass unit (u).
A molecule is the smallest unit of an element or compound that retains its chemical identity.
Molecular Types: Can consist of identical atoms (e.g., O2) or different atoms (e.g., H2O).
Ions: Charged particles (cations: positive, anions: negative); for example, sodium chloride consists of Na+ and Cl− ions.
Represent composition using symbols and valencies.
The cation's symbol precedes the anion's.
Ensure charges balance; use parentheses for polyatomic ions.
Molecular mass: sum of atomic masses; e.g., water (H2O = 18 u).
Formula unit mass: applies to ionic compounds calculated based on empirical formulas.
Understanding principles of matter composition provides a foundation for modern chemistry, crucial for exploring chemical behavior and interactions.