Transcript Atomic Structure and the Periodic Table

Atomic Structure and the Periodic
Table
Chapter 2-1
Chemical symbols
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Abbreviated way to write the name of an
element
Always starts with a capital letter
If double letters – first is capitalized
second is lower case
Cl
Ar
Ne
atom
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Smallest part of matter
Basic building block of matter
Parts of an atom
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Nucleus – center
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protons - + charge
neutrons - neutral charge
size: mass p = mass n
Electron cloud
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Surrounds the nucleus
Contains electrons
Electrons have a negative charge
Size: mass e = 1/2000 of m p
mass so tiny that it isn’t even considered
in the mass of an atom
Moves around the nucleus at such speeds that they
cannot be seen.
Cloud like appearance
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Neutral atom – the
number of positive
charges equal the number
of negative charges
All elements on periodic
table are stable atoms.
Atomic number
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Number of protons in an atom
Every atom of the same element has the same
atomic number
Identity number of an element
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Danish scientist
Neils Bohr
1913
Developed the first
model of what the atom
looks like
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Bohr diagram
Central nucleus
Electrons moving around
it in well defined paths or
orbits.
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Electron clouds
Electrons moving so fast
that they cannot be seen
Electrons move within a
certain region NOT on
orbits
Energy Levels and Electrons
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Electrons are at varying
distances from nucleus
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e near nucleus – low
energy
e farther from nucleus –
high energy
Energy levels
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Each holds a different
amount of electrons
There is a maximum
number of electrons each
can hold
1st
2nd
3rd
4th
2e
8e
18 e
32 e
Mass number
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Number of protons + neutrons in nucleus
Number of Neutrons
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Mass number - # p = #n
Isotopes
Atoms of the same element
that have a different
number of neutrons
Average atomic mass –
average mass of an
element and its isotopes
Written H-1 H-2 H-3
element – mass #
Isotopes of hydrogen
H-1 protium
H-2 deuterium
H-3 tritium
Importance of Isotopes
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Used in:
Medical field –
radioactive to detect
cancers, thyroid
disorders
Dating – to date age of
rocks or artifacts
Radioactive power
plants