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Transcript
Chemistry
The structure of the atom.
The Atomic Theory:
• All matter is made of atoms, which are
particles too small to be seen.
• Each element has its own kind of atom.
The evolution of the atomic Theory:
1. Dalton
2. Rutherford’s gold foil experiment
3. BohrAllmodels
matter is composed of atoms
4. Quantum
Mechanics
Atoms cannot
be made or destroyed
All atoms of the same element are identical
Different elements have different types of atoms
Chemical reactions occur when atoms are
rearranged
Compounds are formed from atoms of the
different elements coming together.
Sub Atomic Particles
Subatomic Charge
Particle
Proton
Mass (Amu) Where it is
Atomic mass located in an
atom
units
+
1
Inside the
nucleus
Neutron
0
1
Inside the
nucleus
Electron
-
Basically 0
Orbiting
outside the
nucleus
The Modern Theory of Atomic
Structure:
• Atomic number: The number of protons
in the nucleus of an atom of that element.
– Gives the number of electrons in a neutral
element.
– Gives the order of elements on the periodic
table
– If an atom gains or loses a proton it not only
changes its atomic number, it also becomes
a new element.
The Modern Theory of Atomic
Structure:
• Mass number: is the total number of protons
and neutrons in the nucleus of an atom
• How do we find the number of Neutrons?
(mass number) - (atomic number) =# of neutrons
Bohr’s Model of Electrons:
• Suggested that electrons move around
the nucleus of an atom in orbits or shells.
• Each orbit is a certain distance from the
nucleus and contains a definite number
of electrons.
• The orbits are filled in a routine way:
– First orbit: 2 electrons
– Second orbit: 8 electrons
– Third orbit: 8 electrons
Bohr model of Nitrogen:
• Check your periodic table for Nitrogen
-3
7
N
Nitrogen
14.0
Bohr model for Magnesium:
Bohr Model for Argon
Isotopes
•
•
Atoms of the same element that have
different numbers of neutrons
Two ways to recognize isotopes:
1. Isotope Name: Chemical name – mass #
– Example: Carbon -11, Carbon -12, Carbon -13
2. Isotope Symbol:
•
Example:
Mass number
X
atomic number
Chemical
Symbol of
element
Isotopes:
• The Isotope symbol makes it easy to find
the number of neutrons
Atomic mass:
• The weighted average of the mass an
element’s naturally occurring isotopes.
• A “weighted average” means you take into
account the % of each isotope that is
present in an ordinary sample of the
element.
Example:
A particular sample of carbon has 10%
carbon-11, 80% carbon-12, and 10%
carbon-13. Calculate the atomic number
of this sample of carbon.