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Atomic Structure
Chapter 4
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Elements are composed of extremely small
particles called atoms.
Structure of Atoms
Structure of the Atom
Subatomic Particles
Mass
(g)
Particle
-
Charge
(Coulombs)
-28
-19
-1
1.67 x 10-24 +1.6 x 10-19
+1
Electron (e ) 9.1 x 10
Proton (p+)
Charge
(units)
Neutron (n) 1.67 x 10-24
-1.6 x 10
0
0
mass p = mass n = 1840 x mass e-
2.2
Particle
Charge
Mass
(atomic
mass units)
1
Location
Proton
positive
+
Neutron
neutral
Ø
1
nucleus
Electron
negative
-
0.0006
orbit, level,
cloud
nucleus
• Nucleus
– Center of the atom
– Protons and neutrons
– 99.9% of the atom’s mass is here
– About 100,000 times smaller than the entire
atom
Atomic Number = number of protons in atom
- identifies the element
- only constant number
Atomic Mass = mass of protons AND neutrons
Counting p, e, n
Atomic number = number of protons in nucleus
Atomic Mass number = number of protons + number of neutrons
Number of Neutrons = rounded atomic mass – atomic number
Number of electrons = Number of protons (in a neutral atom)
Element
Hydrogen (H)
Oxygen (O)
Copper (Cu)
Barium (Ba)
Iodine (I)
# of protons
# of electrons
# of neutrons
Isotopes
Alternative forms of an element that differ in
their number of neutrons
How are these atoms different from each other?
2.3
Writing Symbols for Isotopes
Mass Number
X
Atomic Number
1
1H
235
92
Element Symbol
2
1H
U
3
1H
238
92
U
Do You Understand Isotopes?
How many protons, neutrons, and
electrons are in--
14
6
C
11
6
C?
?
6 protons, 8 (14 - 6) neutrons, 6 electrons
How many protons, neutrons, and
electrons are in-6 protons, 5 (11 - 6) neutrons, 6 electrons