Name _______________________________________
Date _______________ Period _______
Vocabulary – Atomic Structure
Atom – the smallest piece of matter that still retains the property of the element.
Quarks – Very small particles of matter that make up protons and neutrons; presently six different types
of quarks are known.
Early Theories of matter
1. Democritus – Greek philosopher who held that matter was composed of elementary particles, called atoms
2. Aristotle – Greek philosopher who modified an earlier theory that matter was made of four “elements”:
earth, fire, water, air. Aristotle was wrong. However, his theory persisted for 2000 years.
3. Alchemists (about 1000-1650) – Scientist who used chemistry and magic. Made many discoveries
without knowing why. Attempted to (1) change lead and other base metals to gold; (2) discover a
universal solvent; and (3) discover a life-prolonging elixir. Used plant products and arsenic
compounds to treat diseases.
4. Lavoisier, A. L. - Generally regarded as the father of chemistry. Discovered nitrogen; studied
acids and described composition of many organic compounds.
5. Mendeléev, D.I. - Discovered periodicity of the elements and compiled the first Periodic Table
6. John Dalton – Proposed a theory to explain the laws of conservation of matter, definite proportions, and
multiple proportions.
Dalton’s atomic theory
 All matter is made of atoms.
 Atoms of an element are identical.
 Each element has different atoms.
 Atoms of different elements combine in constant ratios to form compounds.
 Atoms are indestructible and only were rearranged during chemical reactions
7. J.J. Thomson – Used a cathode tube (2 electrodes in a vacuum) to detect electrons
8. Robert Millikan – Accurately determined the mass of an electron to be 1/1840 the mass of a proton and the
electron’s charge to be 1-.
9. Ernest Rutherford – Determined that nearly all the atoms mass is concentrated in a very small region in the
center of the atom called a nucleus and that the nucleus contained positive charged particles called protons.
10. Chadwick – Demonstrated the existence of the neutron, a nuclear particle having no charge but with nearly
the same mass as a proton
11. Niels Bohr – Suggested that electrons in an atom move in set paths around the nucleus in energy levels
much like the planets orbit the sun in our solar system.
Subatomic Particles
Nucleus – the center of an atom; made up of protons and neutrons
Proton – A positively charged subatomic particle in the nucleus of an atom
Neutron – A neutral subatomic partial in the nucleus of an atom
Electron – a tiny negatively charged subatomic particle moving around outside the nucleus of an atom
Particle
Symbol
Electrical
Charge
Relative
Mass
Electron
e-
1-
1/1840 (0)
Proton
Neutron
p+
n0
1+
0
1
1
Location
Moving around
outside the nucleus
Nucleus
Nucleus
Actual
Mass (g)
9.11 * 10-28
1.673 * 10-24
1.675 * 10-24
1
Name _______________________________________
Date _______________ Period _______
Models of the Atom
 Electron Cloud model – A diagram to represent electrons as a cloud around the nucleus
 Bohr Model – A diagram to represent electrons as orbits around a nucleus similar to planets around the sun.
 Dot diagram – A diagram to represent electrons in the outer energy level of an atom; uses the element
symbol and dots
Isotope – Atoms of the same element that have different numbers of neutrons’ for example, C-14 and C-12
Atomic mass
14
Atomic mass
12
Atomic number
6
Atomic number
6
C
C
Atomic number – The number of protons in an atom’s nucleus
Average atomic mass – The average mass of an element is the average mass of the mixture of its isotopes
Energy levels – any of the possible energies an electron may have in an atom.
Maximum number of electrons within each energy level
1st level: 2
2nd level: 8
3rd level: 18
Electrons are placed in levels 3-5 before
4th level: 18
completing previous energy level
5th level: 32
Models of the Atom
Electron Cloud model – A diagram to represent electrons as a cloud around the nucleus
Bohr Model – A diagram to represent electrons as orbits around a nucleus similar to planets around the sun.
Dot diagram – A diagram to represent electrons in the outer energy level of an atom; uses the element
symbol and dots
Orbital – a region in an atom where there is a high probability of finding electrons. Each energy level contains one
or more orbital
S orbits contain 2 electrons (1 set of 2 electrons)
P orbits contain 6 electrons (3 sets of 2 electrons)
D orbits contain 10 electrons (5 sets of 2 electrons)
F orbits contain 14 electrons (7 sets of 2 electrons)
Heisenberg Uncertainty Principle – It is not possible to know precisely both the velocity and the position of a
particle at the same time
Aufbau principle – states that each electron occupies the lowest energy orbital available.
Pauli Exclusion Principle - an atomic orbital may describe at most two electrons. To occupy the same orbital, two
electrons must have opposite spins; that is, the electron spins must be paired.
Hund’s rule - states that electrons occupy orbitals of the same energy in a way that makes the number of electrons
with the same spin direction as large as possible
Electron configuration – The arrangement of electrons in an atom.
Example: Nitrogen
1s2 2s2 3p3
2
Name _______________________________________
Date _______________ Period _______
Aufbau chart
1s
2s
2p
3s
3p
3d
4s
4p
4d
4f
5s
5p
5d
5f
6s
6p
6d
6f
7s
7p
7d
7f
3