chem unit 2.1

Democritus

First proposed existence of atoms (400 B.C.)

Atomos

Greek term meaning 'indivisible particle'.

Aristotle

Rejected atomic theory; favored four elements.

John Dalton

Proposed atomic theory with experimental evidence.

Dalton's Theory

Four postulates explaining atomic structure.

Indivisible Particles

All elements consist of indivisible atoms.

Identical Atoms

Atoms of the same element are identical.

Whole Number Ratios

Atoms combine in fixed whole number ratios.

Chemical Reactions

Atoms rearrange during chemical reactions.

Isotopes

Atoms of the same element with different masses.

J.J. Thomson

Discovered the electron using cathode ray tube.

Plum Pudding Model

Thomson's model of atom with electrons in positive sphere.

Robert Millikan

Measured electron charge using oil-drop experiment.

Negligible Mass

Mass of electron is significantly smaller than atoms.

Ernest Rutherford

Discovered nucleus using gold foil experiment.

Gold Foil Experiment

Demonstrated atom is mostly empty space.

Alpha Particles

Positively charged particles used in Rutherford's experiment.

Nucleus

Small, dense, positively charged center of atom.

Static Electricity

Study of electric charges at rest.

Cathode Ray Tube

Device used to study electron behavior.

Oil-Drop Apparatus

Method to measure electron charge accurately.

Experimental Evidence

Data supporting scientific theories and models.

Alpha Particles

Positively charged particles in atomic physics.

Nucleus

Dense, positively charged center of an atom.

Bohr Diagram

Illustrates electrons orbiting nucleus in energy levels.

Electrons

Negatively charged particles orbiting the nucleus.

Solar System Model

Electrons compared to planets orbiting the sun.

Electron Cloud Model

Describes electrons in probabilistic regions around nucleus.

Orbitals

Three-dimensional regions where electrons are likely found.

Heisenberg's Uncertainty Principle

Limits simultaneous measurement of electron speed and position.

Quantum Mechanics Theory

Framework explaining atomic behavior and electron arrangements.

Neutron

Neutral particle with mass equal to proton.

Atomic Number

Number of protons in an element's nucleus.

Atomic Mass

Weighted average mass of an element's isotopes.

Isotope

Atoms with same protons, different neutrons.

Mass Number

Total number of protons and neutrons combined.

Finding Neutrons

Calculated by mass number minus atomic number.

Oxygen Atomic Number

Oxygen has an atomic number of 8.

Oxygen Atomic Mass

Oxygen's atomic mass is approximately 15.999.

Protons

Positively charged particles defining element identity.

Electrons in Neutral Atoms

Equal number of protons and electrons.

Average Atomic Mass Calculation

Based on relative abundance of isotopes.

James Chadwick

Discovered the neutron in 1932.

Isotopes

Atoms of the same element with different neutrons.

Mass Number

Total number of protons and neutrons in an atom.

Atomic Number

Number of protons in an atom's nucleus.

Isotopic Notation

Symbol representing an isotope's mass and element.

Hyphen Notation

Format: Element-Mass Number (e.g., Carbon-12).

Chlorine Isotopes

Common isotopes: 35.45 amu (75%), 37.29 amu (25%).

Calculating Atomic Mass

Use isotope masses and their abundances.

Cations

Positively charged ions formed by losing electrons.

Anions

Negatively charged ions formed by gaining electrons.

Ionic Charge

Indicates electrons gained or lost by an atom.

Sodium Cation

Na+1, formed by sodium losing one electron.

Calcium Cation

Ca+2, formed by calcium losing two electrons.

Oxide Anion

O-2, formed by oxygen gaining two electrons.

Chloride Anion

Cl-1, formed by chlorine gaining one electron.

Abbreviations for Ions

Include mass number, atomic number, and charge.

Indium Isotopes

One isotope mass: 114.9041 amu, 95.795% abundance.

Average Atomic Mass Calculation

Combine isotopes' masses weighted by their abundance.

Percentage Abundance

Fraction of each isotope in a sample.

Element Name Change

Anions named with '-ide' suffix.

Example of Isotope Calculation

Chlorine: (0.7500)(35.45) + (0.2500)(37.29).

Final Atomic Mass of Chlorine

Calculated average: 35.91 amu.

Final Atomic Mass of Indium

Calculated average: 113 amu.