Transcript What is an electron?

Electron Basics
Atom Review
 Protons and
neutrons are bound
together to make
the atomic nucleus
 Protons have a
positive electrical
charge
 Neutrons are
neutral and have no
electrical charge
What is an electron?
 It is a sub-atomic
particle that can be
found around the
atomic nucleus.
 It has a negative
electric charge
 Its mass is about
2000x less than a
proton or neutron
Where is an electron?
 Danish physicist Neils Bohr
proposed the idea that
electrons can be found
around the nucleus in
different energy levels or
shells.
 One cannot pinpoint the
location of an electron,
only about where it is in a
specific energy level or
shell
Electron Shells
 There are 7 electron shells (How many
periods, or rows are on the periodic
table?)
 Each shell can hold a specific number
of electrons
 # of elements in the period = # of
electrons that shell can hold
 Q: How many electrons can the 2nd
electron shell hold?
 A: 8
Electron Shell Capacity - 1st
18 elements
 1st Shell: 2 e 2nd Shell: 8 e 3rd Shell: 8 e Electrons fill each
shell from the inside
out. Ex: the 1st
shell is filled first
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Valence Electrons
 Electrons in the outermost shell are
called valence electrons.
 They are involved in chemical bonding
and reactions.
 We will talk much more about these
electrons when we talk about chemical
reactions in later chapters.
Bohr Diagrams
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 A conceptual model of
an atom
 # of n and # of p are
written in the nucleus
(center circle)
 # of e- are filled in
each shell until it is full
(How many can each
shell hold?)
 Once a shell is full, you
add another circle and
continue.
Bohr Diagram Practice
 Pick 3 elements from the first 18
elements, and create Bohr Diagrams
for those elements.