GENERAL CHEMISTRY: Chapter 2 Atoms, Molecules, and Ions

Dalton’s Atomic Theory

1. Matter is composed of small particles called atoms. Atoms are the smallest unit of an element and can participate in chemical changes

2. An element consists of only one type of atom. That atom’s mass is also a characteristic of that element and is the same for all atoms of that element.

3. All atoms of one element differ from atoms from all other elements

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

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

law of conservation of matter

if atoms are neither created nor destroyed, then the total mass of the matter after it changes from one type to another remains constant

subatomic particles

smaller particles within atoms, that allow atoms to differ fro one another

atomic structure

the identity and arrangement of subatomic particles in each atom

law of definite proportions

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

• discovered the electron through the cathode ray tube experiment

• the beam always deflected toward the positive charge and away from the negative charge

• Thomson was able to calculate the charge to mass ratio of the cathode ray particles

electron

• negatively charge subatomic particle

• mass more than 1000x less than an atom

• 5.60× 10^-9 g/C mass to charge ratio

Robert A Millikan Oil Drop Experiment

• created microscopic oil droplets that were electrically charged

• these droplets could be slowed or reversed by an electric field

• millikan was able to determine the charges on these individual drops

ions

a group of atoms that are negatively or positively charged

ernest rutherford’s gold foil scattering experiment

• aimed a beam of alpha particles at a think piece of gold foil

• volume that an atom occupies is consists of a large amount of empty space

• nucleus makes most of atoms mass

• protons in the nucleus electrons surrounding it

isotopes

atoms of the same element that differ in mass

neutrons

subatomic particles with no electrical charge and have about the same mass as protons

angstrom A

diameter of an atom 10^-10

atomic mass unit

1.6605×10^-24

Atomic Number (Z)

number of protons in an atom; its value determines the identity of an atom—defining trait of an element

neutral atom

contains the same number of protons and electrons, so the atomic number can represent the electrons as well

Mass number (A)

total number of protons and neutrons in an atom

molecular formula

a representation of a molecule or compound that consists of chemical symbols and a subscript to indicate the number of each type of atom in the molecule

empirical formula

the simplest whole number ratio of the number of atoms or ions in a compound

isomers

compounds with the same chemical formula but different molecular structures