Development of the Atomic Model

Atomos: cannot be divided Solid balls

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

Atom can be subdivided. Discovered electrons. Plum pudding model

Oil drop experiment Charge of an electron

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

Hund’s 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

Wave nature of electrons Orbitals

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

Neutron number = mass number – atomic number

Average atomic mass equals the sum of the masses of each isotope times its abundance.

Refer to your average atomic mass lab Refer to pages 172-177

Electrons exist in probability clouds called orbitals.

The 4 currently identified orbitals are: s p d f

Others have been postulated

Sphere 2 electron max

6 electron limit 3 suborbitals, 2 electrons each

10 electron limit 5 suborbitals, 2 electrons each

14 electron limit 7 suborbitals, 2 electrons each

Like electron addresses 4

Principal Orbital or azimuthal Magnetic Spin

Measures energy level Values range from 1-7

Indicates orbital: s, p, d, f s=0 p=1 d=2 f=3

Indicates which suborbital

2px

2py

2pz

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.