Download electrons - Northside Middle School

Atomic Structure
•
•
•
Elements are made of
atoms
The word atom is derived from the Greek
word atom which means indivisible. The
Greeks concluded that matter could be
broken down into particles to small to be
seen. These particles were called atoms
Atoms are composed of three type of particles:
protons, neutrons, and electron. Protons and
neutrons are responsible for most of the atomic
mass.
For example: in a 150 person 149 lbs, 15 oz are
protons and neutrons while only 1 oz. is
electrons. The mass of an electron is very small
(9.108 X 10-28 grams).
The Structure of
Atoms
•
•
•
Atoms have 3
components: protons,
neutrons, and electrons
protons and neutrons
are in the nucleus
Electrons circle around
the nucleus in “electron
shells”.
Protons, Neutrons, and
Electrons
•
•
Protons are found in the nucleus. Protons are
positively charged particles.
Neutrons are also found in the nucleus. Neutrons are
neutral (not electrically charged) charged particles.
•
Almost all of an atoms mass is found in the
nucleus. Electrons don’t really figure into the
atomic mass.
• Electrons are very light and very small.
They are
negatively charged and are found in the electron
shells surrounding the nucleus
Evolution of Atomic Knowledge
Cue Ball
Model
Rutherford
Model
Cube
Model
Plum Pudding
Model
Borh Model
Electron cloud
Model
Saturanian
Model
• “Pictures” of atoms are often misleading:
– Electrons don’t “orbit” the nucleus like planets around the
sun. We often draw them that way because it is easier to
understand, but they really behave like a cloud around
the nucleus, almost like a beehive.
Here are some actual “pictures” of
atoms:
Electron Shells- The
Bohr Model
•
•
•
•
Electrons circle the nucleus
at defined positions called
shells.
The innermost shell of every
atom could hold 2 electrons
(except hydrogen, which only
has 1 electron).
The second shell holds 8
electrons, the 3rd holds 18.
Electrons fill in from the
nucleus out, so the inner
shells always fill up first.
Electrons fill in from the
nucleus out, so the inner
shells fill up first..
Build an Atom
The outermost electron shell is referred to as the
valence shell. Sometimes, atoms do not fill their
valence shell all the way. Some spots are empty.
Structure of Atoms
Elements that have empty spots in their valence
shell are reactive, meaning they want to bond with
other elements, to try to fill up their empty spots.
This is why the alkali metals are
sooooo reactive. They all have
really empty valence shells.
They each only have one
electron in their valence shell!
Nobel gases are not reactive
because they have full valence
shells!
•All of the elements except the 7
elements considered “noble gases”
have empty spots in their valence
Structure of Atoms
shell.
•When elements bond with other
elements they form something called
a compound.
•In a compound, two elements either
share their electrons, or one element
steals the other elements electrons.
Either way, the elements both feel like
their valence shell is fuller than it used
to be, so they are more stable.
•This is why there are so many
compounds in our world. Elements
form compounds to make a full outer
shell.
Meet Oxygen