Transcript Atomic Structure

Atomic Structure Notes
• All atoms consist of a small, massive
nucleus surrounded by smaller, lighter
electrons
• The nucleus consists of protons and
neutrons
• The electrons are negatively charged,
protons are positively charged, neutrons are
neutral (zero charge)
4
# of Protons = # of Electrons
Atomic Number
Be
Beryllium
9.012
Protons (+)
Neutrons
Electrons (-)
Chemical Symbol for Element Beryllium
Protons + Neutrons = Atomic Mass
• Because atoms are so small they are
measured using Atomic Mass Units (AMU)
• Hydrogen is one AMU and is used as a
“measuring stick” for all other atoms
• One Proton is about 1 AMU
• One Neutron is about 1 AMU
• It takes about 2000 Electrons to make one
AMU
Valence Electrons
• The electrons furthest from the nucleus
are called valence electrons.
• These electrons are involved in the
formation of chemical bonds.
• A chemical bond forms between atoms
when valence electrons are shared or
transferred between two or more atoms.
Atoms Are Neutral
• The number of protons(+) and electrons(-)
in an atom are equal; the overall atomic
charge is zero, therefore the atom is
electrically neutral.
Electron Dot Diagram
• Electron Dot Diagrams are used to show
the number of valence electrons present in
an atom. Here is an atom of Sodium
Na
,
,
,
,
,
Electron Dot Diagram
• Here is an electron dot diagram for
oxygen.
,
,
,
,
,
,
,
,
,
,
,
,
,
,
,
,
,
,
O
,
,,
,,
,,
,,
,
Electrons in Orbit
•
Electrons are held in stable ORBITS
(ENERGY SHELLS) around the nucleus
by a balance between two opposing
forces:
1st Force Holding the Electrons in
Orbit
•
The force of electrostatic attraction pulls
the negative electron inward, towards the
positive nucleus.
2nd Force Holding Electrons In
Orbit
•
The 2nd force is an outward force. It is
caused by the accelerating electron
known as the CENTRIPETAL FORCE
(Same force present when swinging a
rock on the end of a string.)
Electron Configuration
• Only two electrons can fit in the first orbit. It is
then considered full so remaining electrons need
to be placed in the second, third, fourth, etc…
orbits.
• Many periodic tables will tell how many electrons
are found in each orbit.
• If an atom is in the 1st row of the periodic table
(period) it will have one orbit. If an atom is in the
second row it will have two orbits. Third row will
have three, and so on.
Location in the Periodic Table.
• This atom is found in the second row. It
has two orbits.
• It has four red protons so it is Atomic #4 in
the periodic table. What is its name?
Use your
periodic table
to identify.
Practice Drawing
• Draw an atom of Nitrogen and label all of
its particles.
How Did You Do?
• Nitrogen is in the second row so it has two
orbits surrounding its nucleus.
• The nucleus should contain 7 protons.
• There should be 7 total electrons. 2 in the
first orbit and 5 in the second orbit.
• Figure the number of neutrons by
subtracting the number of protons from the
atomic mass. (14 – 7) = 7 Neutrons.
Questions About Atoms
• Visit the link below and select 5 questions
about atoms that you would like the
answer to.
• Summarize the question and the answer
on the next page of your composition
notebook.
• http://education.jlab.org/qa/archive_idx.
html