Atomic Structure and Periodic Trends

average atomic mass

weighted average of masses of all naturally-occurring isotopes of that element

ionization energy (IE)

the energy required to remove an electron from a gaseous atom

electron affinity (EA)

the energy change required to add an electron to a gaseous atom

first ionization energy (IE1)

energy required to remove the most loosely bound electron

atomic radius

size of an atom; distance between the nucleus and outermost electron

alpha particles

high-speed positively charged particles produced from the decay of radium

• used by Rutherford in his gold foil experiment

atomic number (Z)

number of protons in the nucleus of an atom, defines an element's identity

Dalton's Atomic Theory

1. Matter is composed of exceedingly small particles called atoms.

2. An element consists of only one type of atom, which has a mass that is characteristic of the element.

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 ratio.

5. Atoms are neither created nor destroyed during a chemical change.

electron

a negatively charged subatomic particle

fundamental unit of charge

the magnitude of the charge of an electron

isotopes

atoms of the same element that differ in mass (number of neutrons)

Law of Constant Composition/Definite Proportions

all samples of a pure compound contain the same elements in the same proportions 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 small, whole-number ratios

mass number(A)

total number of protons and neutrons

Bohr's Model

Planetary Model: included a small, dense nucleus surrounded by orbiting electrons

Plum Pudding Model (Thomson)

described a positively-charged mass with an equal amount of electrons embedded in it

electronegativity

the ability of an atom in a compound to attract electrons from another atom in the compound

Democritus

Greek philosopher who was the first to suggest the existence of atoms, small indivisible particles

atomic mass unit (amu)

1/12 the mass of a single C-12 atom

number of electrons

mass number (A) - atomic number (Z)