5 principles Atoms are basic building block Atoms of same element are identical Atoms of different elements are different Atoms of different elements can combine in definite proportions to form compounds Atoms are indivisible by chemical processes First use of symbols
Gold foil experiment Atom is mostly empty space Atom has a small, dense, positively charged nucleus at its center.
Bohr noticed a constant quantum leap Reasoned that electrons could not be random Reasoned that they were in set orbits, set distances away from nucleus. Planetary orbital model
Bombarded Be with alpha particles New beam produced Not deflected by magnetic field, ie not charged Approx same mass as protons The neutron
Heisenberg Uncertainty Principle: you cannot know both the velocity and position of an electron in motion Pauli Exclusion Principle: no two electrons can have the same four quantum numbers Schroedinger equation: predicts the wave nature of an electron Hunds Rule: unoccupied orbitals will be filled before occupied orbitals are reused Aufbau principle: electrons fill orbitals starting at the lowest available (possible) energy states before filling higher states
Proton Neutron Electron Protons and Neutrons are composed of quarks
In the nucleus Positive charge About 1840 x larger than electron Mass = 1
In the nucleus No charge About 1840 x larger than electron Mass = a little bit more than 1
Outside the nucleus in the electron cloud Negative charge About 1/1840 as large as a proton Mass = essentially 0
The number of protons is the atomic number. This identifies an element. If the proton number changes, the element changes
Isotope: a different version of an element. All chemical properties remain the same. The only difference is neutron number, and this can cause some isotopes to be radioactive. Mass number: protons + neutrons. This identifies an isotope.
The number of protons is the atomic number. This identifies an element. If the proton number changes, the element changes Mass number identifies an isotope
Satisfies the Pauli exclusion principle Since electrons in the same orbital must have opposite spins Values are EITHER + ½ or – ½
First, learn the order of orbital filling. The slant diagram will help you with this. Second, remember the orbital capacities. s: 2 electrons, p: 6 electrons, 3 suborbitals, d: 10 electrons, 5 suborbitals, f: 14 electrons, 7 suborbitals You can count these on the chart
Electrons are energized by the flame. They jump to a higher energy level (quantum leap). When they fall down to their ground state, they fall the same distance and release the same amount of energy (quanta) as light each time, so its always the same color.