CHEM 1411 Chapter 2: Atoms, Molecules, and Ions

Flashcards for Chapter 2 of CHEM 1411, covering atoms, molecules, and ions.

Atomos

Small, finite, indivisible particles of which all matter is composed, according to Leucippus and Democritus.

John Dalton

Published hypotheses about matter in 1807.

Dalton’s Atomic Theory - 1st point

Matter is composed of very small, indivisible particles called atoms. An atom is the smallest unit of an element that can participate in a chemical change.

Dalton’s Atomic Theory - 2nd point

An element consists of only one type of atom, which has a mass that is characteristic of the element and is the same for all atoms of that element

Dalton’s Atomic Theory - 3rd point

Atoms of one element differ in properties from atoms of all other elements.

Dalton’s Atomic Theory - 4th point

A compound consists of atoms of two or more elements combined in a small, whole-number ratio. In a given compound, the number of atoms of each of its elements are always present in the same ratio.

Dalton’s Atomic Theory - 5th point

Atoms are neither created nor destroyed during a chemical change, but are rearranged to yield substances that are different from those present before the change.

Law of Definite Proportions or the Law of Constant Composition

All samples of a pure compound contain the same elements in the same proportion by mass.

Law of Multiple Proportions

When two elements react to form more than one compound, a fixed mass of one element will react with masses of the other element in a ratio of small, whole numbers.

J.J. Thomson

Experimented with cathode ray tubes and calculated the charge-to-mass ratio of cathode ray particles .

Electron

A negatively charged, subatomic particle with a mass more than one thousand times less than that of an atom.

Robert A. Millikan

Determined the charge on individual drops and concluded that 1.6 x 10-19 C was the charge of a single electron.

Thomson's Model of the Atom

Proposed that atoms resembled plum pudding, an English dessert consisting of moist cake with embedded raisins (“plums”).

Ernest Rutherford

Aimed a beam of alpha particles at a very thin piece of gold foil

Rutherford’s Model of the Atom

The atom consists of a very small, positively charged nucleus, where most of the mass of the atom is concentrated. The nucleus is surrounded by negatively charged electrons, which occupy almost all of an atom’s volume.

Isotopes

Atoms of the same element with different masses (different number of neutrons but the same number of protons)

Neutrons

Uncharged, subatomic particles with a mass approximately the same as that of protons.

Atomic number (Z)

The number of protons in the nucleus of an atom.

Mass number (A)

The total number of protons and neutrons in an atom.

Cation

An atom that loses one or more electrons; has a positive charge.

Anion

An atom that gains one or more electrons; has a negative charge.

Chemical symbol

An abbreviation that we use to indicate an element or an atom of an element.

Atomic mass

The weighted, average mass of all the isotopes present in a naturally occurring sample of that element – these values are not whole numbers.

Molecular formula

Indicates the actual number of atoms of each element in a compound.

Empirical formula

Indicates the simplest whole-number ratio of the number of atoms in a compound (it is a reduced formula).

Isomers

Compounds with the same chemical formula but different molecular structures.

Periodic Law

The properties of the elements are periodic functions of their atomic numbers.

Metals

Shiny, malleable, ductile, and are good conductors of heat and electricity.

Nonmetals

Appear dull, are neither malleable nor ductile, and are poor conductors of heat and electricity.

Metalloids

Conduct heat and electricity moderately well, and possess some properties of metals and some properties of nonmetals.

Ionic bond

Attractive forces between objects of opposite charges (cations and anions). Occurs when electrons are transferred and ions are formed

Covalent bond

Attractive forces between the positively charged nuclei and shared electrons. Occurs when electrons are shared and molecules are formed

Monatomic ions

Ions formed from only one type of atom (Mg2+, Na+, Cl-, O2 -, etc).

Polyatomic ions

Ions that contain more than one kind of atom.

Oxyanions

Polyatomic ions that contain one or more oxygen atoms.

Nomenclature

A collection of rules for naming things.

Ionic Hydrates

Ionic compounds that contain water molecules as integral components of their crystals.

Molecular Compounds

Compounds (nonmetal + nonmetal)

Acids

Compounds contain hydrogen.