Transcript Atomic Structure

Development of the Atomic Model
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Atomos: cannot be divided
Solid balls
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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
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First use of symbols
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Atom can be subdivided.
Discovered electrons.
Plum pudding model
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Oil drop experiment
Charge of an electron
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Gold foil experiment
Atom is mostly empty space
Atom has a small, dense, positively charged
nucleus at its center.
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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
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Bombarded Be with alpha particles
New beam produced
Not deflected by magnetic field, ie not charged
Approx same mass as protons
The neutron
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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
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Wave nature of electrons
Orbitals
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Proton
Neutron
Electron
Protons and Neutrons are composed of quarks
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In the nucleus
Positive charge
About 1840 x larger than electron
Mass = 1
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In the nucleus
No charge
About 1840 x larger than electron
Mass = a little bit more than 1
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Outside the nucleus in the electron cloud
Negative charge
About 1/1840 as large as a proton
Mass = essentially 0
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The number of protons is the atomic number.
This identifies an element.
If the proton number changes, the element
changes
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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.
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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
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Neutron number = mass number –
atomic number
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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
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Electrons exist in probability clouds called
orbitals.
The 4 currently identified orbitals are:
s
 p
 d
 f
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Others have been postulated
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Sphere
2 electron max
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6 electron limit
3 suborbitals, 2 electrons each
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10 electron limit
5 suborbitals, 2 electrons each
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14 electron limit
7 suborbitals, 2 electrons each
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Like electron addresses
4
Principal
 Orbital or azimuthal
 Magnetic
 Spin
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Measures energy level
Values range from 1-7
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Indicates orbital: s, p, d, f
s=0
 p=1
 d=2
 f=3
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Indicates which suborbital
 2px
 2py
 2pz
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Satisfies the Pauli exclusion principle
Since electrons in the same orbital must have
opposite spins
Values are EITHER + ½ or – ½
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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
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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.