Transcript Notes 4

Chapter 4: Atomic Structure
4.1: Defining the Atom
I. Early Models
• A. Dalton’s atomic theory:
–
–
–
–
1. All elements made of atoms (True)
2. Atoms of same element identical (False – Isotopes)
3. Different atoms combined to form compounds (True)
4. Chemical reactions happen when atoms joined,
separated, or rearranged (True)
– 5. Atoms of one element can’t be changed into others
through chem. rxn. (False – Nuclear Rxns)
II. Atomic Size
• A. Atom: smallest particle of element that still has
same properties
• B. 100,000,000 copper atoms = 1 cm across
Scanning
Tunneling
Microscopes
can see
individual
atoms
Iron atoms
placed in a
ring on Gold
4.2 Structure of
the Nuclear Atom
I. Electrons (e-)
• A. Very small, negatively charged atomic particles
• B. Discovered by J.J. Thomson with Cathode Ray tube
• C. Electric current sent through gases in tube, light
beam attracted to opposite charges, repel by same
charge
Positive Magnet
Negative magnet
II. Protons and Neutrons
• A. Protons: + charged particles, larger than e• B. Protons discovered in cathode ray tube when
repelled by positive charge
• C. Neutrons: no charge, ~ same size/mass as proton
Carbon Atom
Protons
Neutrons
Electrons
III. Atomic Nucleus
• A. Most thought atoms were evenly spread + and • B. Rutherford shot alpha particles through Gold foil
• C. Expected particles go through because of spread out
+ charge, but some even deflected straight back.
• D. Must be clusters of mass (Nucleus)!
http://www.youtube.com/watch?v=
5pZj0u_XMbc
• E. Nucleus: center of mass, protons and neutrons
• F. Electrons surround nucleus
Electron
Proton
Neutron
Nucleus
4.3: Atomic
Differences
I. Atomic Number
• A. Atomic #: number of
protons in atom
• B. Atoms have no overall
charge
• C. So, number of protons and
electrons are equal
• D. Smaller value number on
periodic table
Atomic
Number
II. Mass Number
• A. Mass #: Total number of Protons
and Neutrons
• B. Average of atomic mass for most
common form of element (round it off)
• C. # of Neutrons = Mass # - Atomic #
• D. Larger value # on periodic table
• Ex. How many protons,
neutrons and electrons does an
atom of Sodium have?
11 protons, 12 neutrons, 11 electrons
Mass
Number
rounded to 7
III. Isotopes
• A. Isotope: atoms with same number of
protons, but different numbers of neutrons
• B. Different mass numbers
• C. Example: Three forms of Hydrogen
– 1. “H –1” (one proton, no neutron)
– 2. “H –2” “Deuterium” (one proton, one neutron)
– 3. “H –3” “Tritium” (one proton, two neutrons)
IV. Atomic Mass
• A. Weighted average mass of an atom
• B. Represents the average of the masses of all
isotopes of an atom considering their abundance
• C. Ex. H –1 is in the most common over H –2,
H –3 so the mass is close to 1 (1.008)
V. Periodic Table Preview
• A. Periods: horizontal rows
• B. Groups: vertical columns (similar properties)
Group
Period