Unit 2: Atomic Structure
Overview- Honors Chemistry
Atomic Structure
Modeling the Atom
History,
experimentation, and
the nature of science
(NOS)
Distinguishing Among
Atoms
Subatomic particles,
vocabulary, isotopes,
and notation
conventions
Introduction to Chemical
Quantities
Atomic mass units, mole
concept, representative
units, conversions,
percent composition
Enduring Understandings
I.
II.
Various models have been used to describe the atom, the smallest particle of an element that retains its identity.
 Chemists and physicists have used experimental evidence to improve atomic models over time.
Dalton’s theory was the foundation for atomic models.
Thomson discovered the electron using a cathode-ray tube and contributed to the plum pudding model.
Rutherford’s gold foil experiment led to the nuclear model.
Atoms are made up of three subatomic particles: protons, electrons, and neutrons
 Atomic number is the number of protons in the nucleus.
 Mass number is the total number of protons and neutrons in an atom.
 Scientists use notation when writing about atoms.
III.
Atoms are primarily composed of empty space.
 Nearly 100% of the mass of an atom is found in its extremely small and dense nucleus.
 The mass of an electron is essentially negligible.
IV.
Isotopes are atoms with the same number of protons but different numbers of neutrons.
 Atomic mass is a weighted average mass of the atoms in a naturally occurring sample of that element.
 Atomic masses are expressed in atomic mass units (amu).
V.
VI.
VII.
A mole, 6.02 x 1023 (Avogadro’s number, NA), is a grouping used by chemists when making calculations.
 Avogadro’s number can be used as a conversion factor that allows one to convert between representative particles and
moles, and vice versa.
 The representative units that make up pure substances are given different names such as atoms, formula units, and
molecules.
Since 1 amu = 1 g/mol, atomic mass values are often referred to as molar masses.
 Molar masses can be used as a conversion factor that allows one to convert between mass and moles, and vice versa.
 Seven elements form diatomic molecules in nature. (Dr. BrINClHOF / The 7’s)
Compounds form when atoms of elements combine in simple whole-number ratios.
 Molar masses for compounds are calculated by adding up the molar masses of atoms.
 Percent composition can be determined using the formula and molar mass of a compound.
 Empirical/molecular formula can be determined using the percent composition of a sample of a compound.