Chemistry Unit 1

John Dalton

Proposed that all matter is composed of atoms and introduced Dalton's Postulates in 1808.

Dalton’s Postulates

Key principles stating that atoms are indivisible, identical for each element, and can combine in whole number ratios.

JJ Thomson

Discovered electrons and proposed the "plum pudding" model of the atom using a cathode ray tube.

Plum Pudding Model

A model of the atom where negatively charged electrons are embedded in a positively charged "cloud."

Ernest Rutherford

Demonstrated that atoms consist mostly of empty space with a dense nucleus at the center through gold foil experiments.

Gold Foil Experiment

An experiment where alpha particles were fired at gold foil, revealing the existence of a small, dense nucleus.

Niels Bohr

Developed a model of the atom where electrons orbit the nucleus in fixed energy levels or shells.

Bohr’s Model

A representation of the atom showing electrons in specific orbits around the nucleus.

James Chadwick

Confirmed the existence of neutrons, which have a mass similar to protons but no charge.

Neutron

A subatomic particle found in the nucleus of an atom, contributing to its mass.

Werner Heisenberg

Introduced the Uncertainty Principle, stating that the position and momentum of an electron cannot both be precisely known.

Heisenberg’s Uncertainty Principle

A fundamental theory in quantum mechanics regarding the limits of measuring particles.

Erwin Schrodinger

Described electrons as waves and developed probability functions to predict their locations in an atom.

Dimitri Mendeleev

Created the first periodic table organized by atomic mass and predicted undiscovered elements.

Periodic Table

A tabular arrangement of elements based on their atomic number and properties.

Period

Horizontal rows in the periodic table indicating the number of energy levels in an atom.

Group

Vertical columns in the periodic table where elements share similar properties due to the same number of valence electrons.

Valence Electrons

Electrons in the highest energy level of an atom that determine chemical properties.

Properties of Metals

Characteristics include being solid at room temperature (except mercury), malleable, ductile, and good conductors of heat and electricity.

Properties of Nonmetals

Can be solid, liquid, or gas; typically brittle, dull, and poor conductors of heat and electricity.

Properties of Metalloids

Elements that have properties of both metals and nonmetals, often semiconductors.

Alkali Metals

Group 1A elements, highly reactive, and never found alone in nature.

Alkaline Earth Metals

Group 2A elements, very reactive but less so than alkali metals, and also never found alone in nature.

Transition Metals

Elements in groups 3B to 2B, all solid at room temperature (except mercury) with various charges.

Noble Gases

Group 8A elements that are unreactive and do not easily form compounds, often found alone in nature.

Lanthanides

Elements in period 6, highly reactive, named after lanthanum.

Actinides

Elements in period 7, highly reactive, named after actinium, with elements after uranium being synthetic.

Representative Elements

Group A elements that include main group elements with predictable properties.

Transition Metals

Group B elements characterized by their ability to form various cations and complex ions.

Boron Group

Group 3A. Properties vary due to containing metals, nonmetals, and metalloids.

Carbon Group

Group 4A. Properties vary due to containing metals, nonmetals, and metalloids.

Nitrogen Group

Group 5A. Properties vary due to containing metals, nonmetals, and metalloids.

Oxygen Group

Group 6A. Often found in minerals with other elements.

Halogens

Group 7A. Most reactive nonmetals. Means “salt former” because compounds with halogens form salts. Highly toxic. Exist in all three states of matter.