Atoms, Molecules, and Ions

Flashcards covering basic atomic theory, subatomic particles, periodic table trends, chemical laws, and nomenclature based on lecture notes.

Law of Conservation of Mass

Formulated by Antoine Lavoisier in 1774, it states that in a chemical reaction, matter is neither created nor destroyed; the total mass of matter remains the same at the end as at the beginning of a chemical change.

Law of Definite Proportions

Summarized by Joseph Proust in 1797, it states that all samples of a given compound, regardless of their source or preparation, have the same proportions of their constituent elements by mass.

Law of Multiple Proportions

Published by John Dalton in 1804, it states that when two elements (A and B) form two different compounds, the masses of element B that combine with $1\,g$ of element A can be expressed as a ratio of small whole numbers.

Dalton's Atomic Theory

Proposed in 1808, it defines elements as composed of small particles called atoms; all atoms of a given element are identical in mass and properties, and chemical reactions involve the rearrangement of these atoms.

Electron

A subatomic particle discovered by J.J. Thomson in his cathode ray tube experiment; it has a negative charge of $-1.60 \times 10^{-19}\,C$ and a mass of $9.10 \times 10^{-28}\,g$.

Millikan's Oil Drop Experiment

An experiment conducted in 1909 by Robert A. Millikan and Harvey Fletcher that accurately measured the electrical charge of an individual electron.

Rutherford’s Gold Foil Experiment

An experiment that revealed the atom's positive charge is concentrated in a tiny nucleus, leading to the discovery of the proton and the nuclear model of the atom.

Nucleus

The central core of an atom containing protons and neutrons; its radius is approximately $5 \times 10^{-3}\,pm$ compared to the atomic radius of $100\,pm$.

Proton

A subatomic particle found in the nucleus with a positive charge of $+1.6022 \times 10^{-19}\,C$ and a mass approximately 1840 times that of an electron ($1.67 \times 10^{-24}\,g$).

Neutron

A neutral subatomic particle discovered by James Chadwick in 1932; it has zero charge and a mass slightly greater than a proton ($1.67493 \times 10^{-24}\,g$).

Atomic Number (Z)

The number of protons in the nucleus of an atom, which defines the identity of the element.

Mass Number (A)

The total number of protons and neutrons in an atom's nucleus.

Isotopes

Atoms of the same element with the same number of protons but different numbers of neutrons, resulting in different mass numbers.

Periodic Law

Summarized by Dimitri Mendeleev, it states that when elements are arranged in order of increasing mass, certain sets of properties recur periodically.

Metals

Elements on the lower-left and middle of the periodic table that are shiny, good conductors of heat and electricity, malleable, and ductile.

Nonmetals

Elements on the upper-right side of the periodic table; they are generally poor conductors and tend to gain electrons during chemical changes.

Metalloids

Also called semimetals, these elements lie along the zigzag line of the periodic table and exhibit properties intermediate between metals and nonmetals.

Group (Family)

A vertical column in the periodic table; elements in the same group often share similar chemical properties.

Period

A horizontal row in the periodic table.

Diatomic Molecule

A molecule containing only two atoms; examples include $H_2$, $N_2$, $O_2$, $F_2$, $Cl_2$, $Br_2$, and $I_2$.

Cation

An ion with a net positive charge, formed when a neutral atom loses one or more electrons.

Anion

An ion with a net negative charge, formed when a neutral atom gains one or more electrons.

Formula Unit

The basic unit of an ionic compound, representing the smallest electrically neutral collection of ions.

Molecular Formula

A chemical formula that shows the exact number of atoms of each element in the smallest unit of a substance.

Empirical Formula

A chemical formula that shows the simplest whole-number ratio of the atoms present in a substance.

Oxoacid

An acid that contains hydrogen, oxygen, and another central element, such as $HNO_3$ (nitric acid) or $H_2CO_3$ (carbonic acid).

Hydrate

A compound that has a specific number of water molecules attached to its formula unit, such as $BaCl_2 \cdot 2H_2O$ (barium chloride dihydrate).

Organic Chemistry

The branch of chemistry dealing with carbon-containing compounds, excluding simple oxides and carbonates like $CO_2$ and $NaCN$.

Alkanes

A class of hydrocarbons consisting of straight-chain or branched carbon atoms bonded with single bonds, such as methane ($CH_4$) and ethane ($C_2H_6$).