Chemistry: Properties and Changes of Matter

Physical Properties

• A characteristic of a substance
• Describes how a substance appears (taste, texture, color)
• Describes a substance's state and changes in state
• Examples of physical properties include taste, texture, color, and state changes

Physical Changes

• A change in matter that does not alter the substance's identity
• Examples include breaking, dissolving, melting, boiling, and freezing

Chemical Properties

• The reactive characteristics of a substance
• Describes how a substance changes into a new substance
• Examples include the reaction of calcium with water and burning paper

Chemical Changes

• A change in matter that alters a substance's identity
• A new substance is formed during a chemical change
• Examples include burning wood, rusting of iron and the reaction of vinegar with baking soda

Elements

• Pure substances that contain only one type of atom
• Found on the periodic table
• Atomic examples include sodium (Na), copper (Cu), lithium (Li), and iron (Fe)
• Diatomic elements: Exist as two atoms covalently bonded together (e.g., H₂, Br₂, N₂)
• Example diatomic elements: "HOBrFINCI"

Molecules

• Consist of two or more atoms bonded together
• Examples include water (H₂O), glucose (C₆H₁₂O₆), and fluorine (F₂)

Compounds

• Molecules containing more than one type of element

The Periodic Table

• A tabular arrangement of chemical elements
• History included in the slides

Dobereiner (1829)

• Developed the concept of "triads"
• Noted that groups of three elements share similar chemical behaviors
• Did not work for all elements

Newlands (1864)

• Organized elements by atomic weight
• Noted that every eighth element had similar properties (Law of Octaves)
• Gaps in the table were not accounted for

Mendeleev (1869)

• Organized elements by atomic weight (and properties)
• Created the Periodic Table as we know it today
• Prediction of undiscovered elements and their properties
• Issues existed with the ordering of elements based on weights

Moseley (1913)

• Arranged the periodic table by atomic number
• Atomic number was more suitable for arranging the elements than atomic mass

History of the Atom

• Ancient Greek philosophers, including Democritus, proposed the concept of atoms as indivisible particles

Democritus (~460 - ~370 BCE)

• Proposed the atomic theory
• First to propose the theory
• Coined the term "atom," meaning indivisible
• No experimental evidence

Aristotle (384-322 BCE)

• Criticized Democritus' theory
• Supported the four-element theory proposed by Empedocles (Earth, Air, Water, Fire).
  • This theory held for nearly 2,000 years later

John Dalton (1766-1844)

• Revitalized atomic theory from the basis of experimental evidence
• Scientist and teacher
• His theories were different from those of Greek philosophers

Dalton's Atomic Theories

• Atoms cannot be subdivided / created / destroyed.
• All atoms of the same element are identical.
• Atoms combine in small whole-number ratios to form compounds

Thompson (1856-1940)

• Discovered the electron
• Proposed the "raisin bun model" of the atom
• Electrons embedded in a positively charged sphere

Ernest Rutherford (1871-1937)

• Conducted the gold foil experiment
• Discovered the nucleus of the atom
• Demonstrated that most of an atom is empty space
• Proved atom contained a densely packed positive core (nucleus)

James Chadwick (1891-1974)

• Discovered the neutron
• Neutral particles in the atomic nucleus, along with protons.