Chapter 2: Atoms, Molecules, and Ions

Millikan

"Oil drop" experiments that helped determine the fundamental charge of a single electron. (1.6 x 10^-19 C).

J.J. Thomson discovery

Using a cathode ray tube, apparatus consisted of a sealed glass tube from which almost all the air has been removed; the tube contained two metal electrodes. When high voltage was applied across the electrodes, a visible beam called a cathode ray appeared between them. The results of these measurements indicated that these particles were much lighter than atoms. Based on observations: The particles are attracted by positive (+) charges and repelled by negative (-) charges so they must be negatively charged (like charges repel and unlike charges attract) they are less massive than atoms and indistinguishable, regardless of the source material, so they must be fundamental, subatomic constituents of all atoms.

Chemical symbol

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

Anion

an atom that gains one or more electrons will exhibit a negative charge

Isotopes

atoms of the same element that differ in mass

Mole

defined as the amount of substance containing the same number of discrete entities as the number of atoms in a sample of pure 12C weighing exactly 12g.

Atomic mass unit (amu)

defined with regard to the most abundant isotope of carbon, atoms of which are assigned masses of exactly 12 amu. One amu is exactly 1/12 of the mass of one carbon-12 atom. 1 amu = 1.6605 x 10^-24 g.

Structural formula

gives the same information as its molecular formulas but also shows how the atoms are connected in the molecule.

Empirical formula

indicates the types of atoms present and the simplest whole-number ratio of the number of atoms (or ions) in the compound.

Avogadro's number (Na)

number of entities composing a mole has been experimentally determine to be 6.022 x 10^23

atomic charge =

number of protons - number of electrons

atomic number (Z)

number of protons in the nucleus of an atom. defining trait of an element: its value determines the identity of the atom.

atomic mass

of a single atom is approximately equal to its mass number.

Ernest Rutherford

performed a series of experiments using a bean of high-speed, positively charged alpha particles (a particles) that were produced by the radioactive decay of radium; a particles consist of two protons and two neutrons. aimed bean of a particles at a very thin piece of gold foil. What they discovered - most particles passed right through the foil without being deflected at all. (some were diverted slightly, and a very small number were deflected almost straight back at the source). Two conclusions: 1. The volume occupied by an atom must consist of a large amount of empty space. 2. A small, relatively heavy, positively charged body, the nucleus, must be at the center of each atom.

Cation

positively charges atoms, formed when an atom loses one or more electrons

Molecular formula

representation of a molecule that uses chemical symbols to indicate the types of atoms followed by subscripts to show the number of atoms of each type in the molecule.

average mass equation

sum (fractional abundance x isotopic mass)

Molar mass

the mass in grams of 1 mole of that substance, a property expressed in units of grams per mole (g/mol).

Mass number (A)

the total number of protons and neutrons in an atom.

Neutron

uncharged, subatomic particles with a mass approximately the same as that of a proton.

Ion

when the number of positively charged protons and negatively charged electrons are not equal, the atom is electrically charged

Dalton's atomic theory

1. Matter is composed of exceedingly small particles called atoms. An atom is the smallest unit of an element that can participate in a chemical change. 2. 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. A macroscopic sample of an element contains an incredibly large number of atoms, all of which have identical chemical properties. 3. Atoms of one element differ in properties from atoms of all other elements. 4. A compound consists of atoms of two or more elements combined in a small, whole-number ration. In a given compound, the number of atoms of each of its elements are always present in the same ratio. 5. Atoms are neither created nor destroyed during a chemical change, but are instead rearranged to yield substances that are different from those present before the change.

Number of neutrons

A - Z

Electron

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