Download 03Atomic_Structure 175KB Sep 13 2012 09:32:33 AM

Atomic Structure
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
masses.
3. Compounds are formed when atoms of
different elements link to form molecules or
ionic compounds.
4. Atoms cannot be created or destroyed in
physical or chemical reactions.
What are the 3 major parts of an
atom?
• 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.
The Proton
• Protons are positively charged particles
found in the atomic nucleus.
• Protons were discovered by Ernest
Rutherford.
The Neutron
• Neutrons are uncharged particles found
in the atomic nucleus.
• They were discovered by James Chadwick
in 1932
The Electron
• 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
atom.
• Chemical reactions involve sharing or
exchanging electrons.
The Nucleus
• The nucleus is the central part of an atom.
It is composed of protons and neutrons.
• The nucleus contains most of an atom's
mass
• It was discovered by Ernest Rutherford in
1911.
What is the Electron Cloud Model?
Model of the atom pictures the electrons moving
around the nucleus in a region called an electron
cloud.
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
order…
• 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)
Ions
• The number of electrons doesn’t always
equal the number of protons … if you have
an ion!!
• It’s not neutral, but has an overall charge
Charges
• 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
number)
– # electrons = 2 more than neutral = 10
– # neutrons = 16 – 8 = 8
K+
• 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
the nucleus.
Therefore, the isotope will have a different mass than the
naturally occurring form of the element (different than what
the periodic table tells us).