Chemistry Basics: Atoms and Molecules

Learning Objectives

• Atoms and molecules are fundamental topics discussed
• Laws of chemical combination are included
• Dalton's atomic theory is a key concept
• Charged particles in matter (electrons, protons, and neutrons) are covered
• Models of the atom are explored
• Valency, atomic number, mass number, isotopes, and isobars are discussed
• Molecules, molecules of compounds, ions and molecular mass are all important concepts.

Discovery of an Atom

• Ancient Indian and Greek philosophers pondered the unseen form of matter
• Maharishi Kanad postulated that dividing matter leads to smallest particles (Parmanu)
• Pakudha Katyāyana elaborated that these particles exist combined
• Democritus and Leucippus proposed that matter can be divided infinitely until indivisible particles (Atoms)
• Antoine Lavoisier established two important laws of chemical combination

Laws of Chemical Combination

• Two fundamental laws are: Law of Conservation of Mass and Law of Constant Proportions
• Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction
• Law of Constant Proportions states that elements in a chemical compound always combine in a fixed ratio by mass

Dalton's Atomic Theory

• Dalton's atomic theory explains the Law of Conservation of Mass
• Matter consists of small particles called atoms
• Atoms are indivisible and indestructible
• Atoms of the same element are identical in mass and properties
• Atoms of different elements have different masses and properties
• Atoms combine in simple whole-number ratios to form compounds

Size of an Atom

• Atoms are very small, smaller than anything imaginable
• Millions of atoms would only make a thin layer
• Atomic radius is measured in nanometers

Symbols of Elements

• John Dalton was the first to use symbols for elements in a specific way
• A symbol represents a specific quantity of that element (one atom)
• Berzelius proposed using one or two letters from the element's name for symbols
• Element names often derive from the place where they were found

IUPAC Nomenclature

• IUPAC (International Union of Pure and Applied Chemistry) standardizes element names, symbols, and units
• The first letter of a symbol is always uppercase, the second lowercase
• Some symbols are derived from Latin, German, or Greek names

Symbols of Some Elements

• A table providing atomic numbers, symbols, and names of various elements

Name of Element and Latin Name

• A table showing the Latin names and symbols of various elements