Download Atomic Structure Theory

Atomic Structure Theory
The Atom
•  Atoms – the smallest part of an element
that cannot be broken down by chemical
reaction.
- The basic unit of all matter
Subatomic Particles
Neutron (n0) – neutrally charged particle making
up the nucleus of the atom. Mass = 1 atomic
mass unit (amu)
•  Proton (p+) – positively charged particles making
up the nucleus of the atom. Mass = 1 atomic
mass unit (amu)
•  Electron (e-) – Negatively charged particle found
in energy levels outside the nucleus. Mass is
negligible – not significant
Chart
Particles
Charge
Mass
Location
Protons
Positive
1 amu
In Nucleus
Neutron
Neutral
1 amu
In Nucleus
Electrons
Negative
Negligible
Out of Nucleus
•  Atomic Number - number of protons in an atom.
–  All atoms of the same element have the same atomic
number
–  All neutral atoms have equal protons and electrons
–  The number of neutrons = mass number – atomic
number
Mass Number
•  Mass Number – the total number of
protons and neutrons in an isotope of an
atom.
–  Mass number = number of protons + number
of neutrons
•  Ex. U-238
–  Isotopes – are atoms of the same element with a
different mass number
•  Ex. Pb – 210 vs. Pb – 206
Atomic Mass
•  Atomic Mass – the atomic mass of an element is
the average mass of the isotopes of that element
in a natural sample. Ex. Carbon = 12.011 amu
•  1 amu = 1/12 the mass of a Carbon-12 atom
•  Boron 11 – 80.0%
•  Boron 10 – 20.0%
•  Atomic Mass of Boron – 10.8amu
•  Isotopes
–  C 12
–  C 13
Mass = P + N
12 = 6p + 6n
11 = 6p + 5n
•  Ions
–  Neutral Atoms
–  Negative Atoms
–  Positive Atoms
p=e
p<e
p>e
Symbols of the Periodic Table
•  Element Symbols often come from Latin
words
–  Gold – Au
–  Mercury - Hg