Download Atomic Structure and Isotopes

Atomic Structure and Isotopes
August 15, 2013
Atomic Structure
(Chapter 4)
An atom is the smallest particle of an element that retains its
identity in a chemical reaction.
The ancient Greek philosopher Democritus believed that atoms
were indivisible and indestructible.
Aug 15­2:30 PM
Democritus's ideas lasted until the late 1700s when John Dalton proposed
Dalton’s Atomic Theory:
> All elements are composed of atoms.
> Atoms of the same elements are the same.
> Atoms of different elements can combine
together to make compounds.
> Chemical reactions occur when atoms are
separated, joined, or rearranged.
Aug 15­2:30 PM
1
Atomic Structure and Isotopes
August 15, 2013
There have been many models of the atom since Dalton introduced his
atomic theory.
1. Dalton's Theory ­ The "Billiard Ball" Model
Aug 15­2:30 PM
2. Thomson’s Theory– The “Raisin Bun” Model
Aug 15­2:30 PM
2
Atomic Structure and Isotopes
August 15, 2013
3. Rutherford’s Theory – “beehive” or “nuclear” model.
Aug 15­2:30 PM
Bohr Theory – The ‘Planet’ Model
Bohr stated that the nucleus contains both protons
and neutrons with electrons in fixed energy levels
around the nucleus.
Aug 15­2:30 PM
3
Atomic Structure and Isotopes
August 15, 2013
The Structure of the Nuclear Atom
Subatomic Particles
• Electrons (e­) are negatively charged subatomic particles that surround
the nucleus of the atom.
• Protons (p+) are positively charged subatomic particles and are found within the
nucleus of an atom.
• Neutrons (n0) are subatomic particles with no charge (neutral). They are found
within the nucleus of an atoms.
Aug 15­2:30 PM
Aug 15­2:30 PM
4
Atomic Structure and Isotopes
August 15, 2013
Distinguishing Among Atoms
Atomic Number
Each element in the periodic table has a unique atomic number.
The atomic number corresponds to the number of protons in the nucleus.
For an element, the number of electrons will equal the number of protons.
Atomic Number
(Number of protons
and electrons)
Aug 15­2:30 PM
Mass Number
The mass number is the total number of protons and
neutrons in the nucleus.
Mass Number = protons + neutrons
Not found on the periodic table!
Aug 15­2:30 PM
5
Atomic Structure and Isotopes
August 15, 2013
Aug 15­2:30 PM
Isotopes
Isotopes are atoms that have the same number of protons, but
different numbers of neutrons.
Therefore, isotopes of the same element will have different mass
numbers.
Aug 15­2:30 PM
6
Atomic Structure and Isotopes
August 15, 2013
Special notation is used to distinguish between different isotopes:
12
13
6
6
C
Carbon­12
C
Carbon­13
Aug 15­2:30 PM
Atomic Mass
The atomic mass is the weighted average mass of the atom’s naturally occurring
isotopes. It is not the mass number!
Atomic Mass
Aug 15­2:30 PM
7
Atomic Structure and Isotopes
August 15, 2013
Aug 15­2:30 PM
Fill in the following table:
Element Name
Number e­
Number of p+ Number of n0 Shorthand
Carbon­12
25
25
Chlorine­35
14
16
50
24
Cr
Aug 15­2:30 PM
8