Basic Concepts of Matter

Science 1st Semester Reviewer

• Pointers:
  • Particle Nature of Matter: elements, compounds, mixtures, atoms, molecules
  • Atomic Structure: protons, neutrons, electrons (isotopes and ions)
  • Periodic Table of Elements: development of atomic theory, arrangement of elements, reactive and non-reactive metals
  • Quantum Mechanical Model (electron configuration)

Particle Nature of Matter

• Matter: Anything that has mass and occupies space.
• Kinetic Molecular Theory/Kinetic Particle Theory: Explains the nature of matter.

Explanation for the Particle Nature of Matter

• Solids:
  • Arrangement: regular array
  • Distribution: packed closely together
  • Attractive Forces: strong attractive forces
  • Movement of Particles: vibrate, rotate, move in fixed positions only
• Liquids:
  • Arrangement: irregularly packed loosely
  • Distribution: moderately strong attractive forces
  • Attractive Forces: moderately strong attractive forces
  • Movement of Particles: vibrate, rotate, and move freely (fluid) and randomly
• Gases:
  • Arrangement: no perceptible arrangement
  • Distribution: farther apart from one another
  • Attractive Forces: negligible attractive forces
  • Movement of Particles: vibrate, rotate, move freely (fluid), randomly, rapidly, not constrained by other particles

Properties of Matter

• Solids:
  • Density: high
  • Compressibility: non-compressible
  • Shape/Volume: has a definite shape and volume
  • Examples: salt, sugar
• Liquids:
  • Density: high
  • Compressibility: slightly compressible
  • Shape/Volume: takes the shape of the container and has a definite volume
  • Examples: water, oil
• Gases:
  • Density: low
  • Compressibility: highly compressible
  • Shape/Volume: takes the shape and volume of its container
  • Examples: helium, air

Physical Properties

• Determined without changing the substance's identity.
• Extensive: depends on the amount of substance (e.g., mass, volume).
• Intensive: does not depend on the amount of substance (e.g., density, color).

Chemical Properties

• Changes the identity of a substance.
• Describes how a substance reacts with air, acid, base, water, and other chemicals.

Particles of Matter

• Atom: basic unit of matter, smallest unit of an element.
• Elements: made up of identical atoms with the same mass, size, and properties.
• Molecules: combination of two or more atoms.
• Compounds: composed of atoms of more than one element.

Laws Governing the Particle Nature of Matter

• Law of Chemical Combination:
  • Law of Definite Proportions: the composition of a substance is the same regardless of the source or method of preparation.
  • Law of Conservation of Mass: matter cannot be created or destroyed, only transformed.
  • Law of Multiple Proportions: when two elements form more than one compound, the ratios of the masses of one element that combine with a fixed mass of the other element are in small, whole-number ratios.

Macroscopic Level

• Visible to the naked eye

Microscopic Level

• Requires an instrument to be seen (atoms,molecules)

Submicroscopic Level

• Only identifiable by behavior

Physical and Chemical Changes in Matter

• Physical change:
  • The material is structurally the same before and after change (examples include melting, shedding, boiling, chopping).
• Chemical change: A change in the chemical composition; often not reversible. (examples include combustion, rotting, rusting, digestion)

Density

• Mass per unit volume (mass/volume)
• Constant for a given substance

Reactive and Nonreactive Metals

• Metals: Most elements, naturally occurring, plentiful, good conductors, malleable.
• Nonmetals: Less common, poor conductors of electricity, brittle

Periodic Trends

• Atomic Radius: Size of an atom, generally decreases across a period and increases down a group.
• Ionic Radius: Size of a cation or anion, generally decreases across a period, and increases down a group.
• Ionization Energy: Energy to remove an outermost electron, generally increases across a period and decreases down a group.
• Electron Affinity: Energy change when an atom gains an electron, generally increases across a period and decreases down a group.
• Electronegativity: Tendency of an atom to attract shared electrons, generally increases across a period and decreases down a group.

History of Atoms

• 1803: John Dalton's solid sphere model (all matter composed of small particles)
• 1904: Thomson's plum pudding model (electrons scattered throughout positive sphere)
• 1911: Rutherford's nuclear model (atom has a dense positively charged nucleus, electrons outside).
• 1913: Bohr's planetary or modified nuclear model
• 1926: Schrodinger's quantum model (electrons behave like waves)

Atomic Structure

• Protons: positive charge
• Neutrons: no charge
• Electrons: negative charge

Isotopes and Ions

• Isotopes: Same atomic number, different atomic masses; differ in number of neutrons
• Ions: Atoms have an imbalance of protons and electrons; when an atom gains or loses electrons

Periodic Table of Elements

• Created through decades of experiments and discoveries by scientists.

Periodic Classification

• Columns (Groups): Similar elements; similar properties of elements.
• Rows (Periods): Correspond to the highest energy level.
• Elements in the same group have similar properties, while elements in the same period have different properties.

Quantum Mechanical Model

• States that electrons are in 3-dimensional regions around the nucleus.
• Atomic orbitals are different shapes.
• The orbitals fill up electron energy levels.

Electron Configuration

• Describes how electrons are distributed in an atom's energy levels.
• Describes the order and distribution of electrons in an atom's orbitals and subshells.
• Aufbau Principle: Electrons fill the lowest energy levels first.
• Pauli Exclusion Principle: A maximum of two electrons can occupy an orbital, with opposite spins.
• Hund's Rule: Electrons fill orbitals separately within a subshells before doubling up.

Questions

• Same electron configuration vs. same element?: Different electron configurations can mean different elements. The electron configuration shows the distribution of electrons among different orbitals within the atom.
• Why is "s" first when distributing electrons?: S orbitals have lower energy levels, and the energy configuration is distributed accordingly.
• Why are d and f orbitals not in the first energy level?: Their high energy levels prevent them from occupying energy level one, thus they are filled in later.