03Atomic_Structure 175KB Sep 13 2012 09:32:33 AM
Transcript 03Atomic_Structure 175KB Sep 13 2012 09:32:33 AM
Modern Atomic Theory:
1. All matter is made of atoms, too small to see.
2. Each element has its own kind of atom.
Atoms of the same element have same mass.
Atoms of different elements have different
3. Compounds are formed when atoms of
different elements link to form molecules or
4. Atoms cannot be created or destroyed in
physical or chemical reactions.
What are the 3 major parts of an
• Proton (+)
• Neutron (no charge)
• Electron (-)
Where is everything located?
Protons and Neutrons are
found in the nucleus (the
central part of the atom)
Electrons orbit the nucleus.
• Protons are positively charged particles
found in the atomic nucleus.
• Protons were discovered by Ernest
• Neutrons are uncharged particles found
in the atomic nucleus.
• They were discovered by James Chadwick
• Electrons are negatively charged particles
that surround the atom's nucleus.
• Electrons were discovered by J. J.
Thomson in 1897.
• Electrons determine properties of the
• Chemical reactions involve sharing or
• The nucleus is the central part of an atom.
It is composed of protons and neutrons.
• The nucleus contains most of an atom's
• It was discovered by Ernest Rutherford in
What is the Electron Cloud Model?
Model of the atom pictures the electrons moving
around the nucleus in a region called an electron
The electron cloud is a cloud of varying density
surrounding the nucleus. The varying density
shows where an electron is more or less likely to
be (it’s always moving so we can’t pinpoint it!)
Calculating #’s of e-, p+ and no
• For Krypton:
– # protons = atomic number = 36
– # electrons = # protons (neutral) = 36
– # neutrons = Atomic Mass – Atomic Number
= 84 – 36 = 48
Can find the information in any
• Atomic Number = 78
• Atomic Mass = 195
• How many electrons, protons and
neutrons and what is it?
– #protons = 78 = # electrons
– # neutrons = 195 – 78 = 117
– What is it?? Pt (Platinum)
• The number of electrons doesn’t always
equal the number of protons … if you have
• It’s not neutral, but has an overall charge
• POSITIVE - The element LOSES
electrons from the neural atom
• NEGATIVE – The element GAINS
electrons from the neutral atom
• The magnitude of the charge tells you how
many electrons are lost/gained
O2• Oxygen has an atomic number of 8
– # protons = 8 (ALWAYS the same as Atomic
– # electrons = 2 more than neutral = 10
– # neutrons = 16 – 8 = 8
• Atomic Number = 19 = # protons
• Positive 1 = Loses one electron = 18
• # neutrons = 39-19 = 20
Isotopes: Different forms of the SAME
element based on the number of NEUTRONS in
Therefore, the isotope will have a different mass than the
naturally occurring form of the element (different than what
the periodic table tells us).