Atomic Structure • Atoms: tiny units that determine the properties of all matter.
Democritus • “atom”: unable to divide • Suggested that the universe was made of invisible units named atoms. • The movements of these atoms caused changes in matter. • Was unable to provide evidence.
John Dalton • 1808 • Proposed another Atomic Theory • Proposed that atoms could not be divided. • Stated that atoms of the same element were all alike, and could join to form compounds. • Considered the foundation of modern Atomic Theory.
Dalton’s Atomic Theory • Elements are made up of atoms • Atoms of each element are identical. Atoms of different elements are different. • Compounds are formed when atoms combine. Each compound has a specific number and kinds of atom. • Chemical reactions are rearrangement of atoms. Atoms are not created or destroyed.
What’s in an Atom? • Nucleus: small, dense center which holds a positive charge. • Protons: in nucleus; positive charge • Neutrons: in nucleus, neutral charge. • These are almost identical in size and mass, but different in charges.
Electrons • Move around the nucleus in a cloud. • Very little mass • Analogy: if the nucleus of an atom were the size of a marble, the atom would be the size of a football stadium.
Properties of Subatomic Particles Guaranteed To Be On Test
Un-reacted Atoms Have No Overall Charge • Have an equal number of protons and electrons. • The charges cancel each other out. • Example: Helium Atom • Charge of two protons = +2 • Charge of two neutrons = 0 • Charge of two electrons = -2 • Total charge of atom = 0
Models of the Atom • Bohr’s Model: Theorized that electrons were in set paths around nucleus like planets around sun (orbits). • Each electron has a certain energy, determined by its path around nucleus. • Must gain energy to move to higher orbit, lose energy to move to lower orbit.
Modern View • The atom is mostly empty space. • Two regions • Nucleus- protons and neutrons. • Electron cloud- region where you might find an electron. • Atoms are really, really tiny: 109 atoms lined up = 1 cm
Electrons in Orbitals • Outer Electrons have more energy because they take the same time to orbit the nucleus but have to go a greater distance so the are faster. • Modern theory has electrons in orbitals vs. orbits; you can predict the location of an orbit, you cannot predict the orbital location.
Orbitals • s, p, d and f orbitals • s orbital: lowest energy level; can hold 2 electrons (sphere shaped) • p orbital: can hold 6 electrons (dumbbell shaped) • d orbital: max 10 electrons • f orbital: max 14 electrons
Energy Levels • Energy Level 1: 2 electrons (s) • Energy Level 2: 8 electrons (s,p) • Energy Level 3: 18 electrons (s,p,d) • Energy Level 4: 32 electrons (s,p,d,f)
Valence Electrons • Electrons in the outermost energy level. • Determine chemical properties and the elements ability to form bonds.