02. Atoms, Ions, and Molecules - The Building Blocks of Matter (2).pptx

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Atoms, Ions, and Molecules: The Building Blocks of Matter
Overview:
1. Dalton’s Atomic Theory
2. History of the Atomic Structure
3. Structure of the Atom
4. Nuclear Chemistry: Balancing Nuclear Equations
5. Ions
6. Average Atomic Mass
7. Molecular Weight (Formula Mass)
8. Mole
9. Empirical Formula vs Molecular Formula
Suggested Readings:
1. Chapter 2
2. Chapter 6.1 – 6.2
3. Chapter 20.1 – 20.3

1. Dalton’s Atomic Theory
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•
Infinitely divisible
(Plato/Aristotle)
•
Ultimate particle (indivisible)
–
Upon division, eventually a
particle is reached which can
no longer be divided. It is
called “atom” - Democritus
(400 BC)
“Nothing exists except atoms and empty space; everything
else is opinion.” - Democritus 460–370 B.C.

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Dalton’s Atomic Theory
1. All matter is made up of atoms
2. Atoms can neither be created nor destroyed
3. Atoms of a particular element are alike
Tiny, hard, indivisible particles
Atoms are unchanged in chemical reactions
All P atoms have the same size, mass and properties
4. Atoms of different elements are different from one another
Pb (lead) is different from Au (gold) in size, mass and properties
5. A chemical reaction involves either the union or the separation of
individual atoms
CH
4
( g ) + 2 O
2
( g ) → CO
2
( g ) + 2 H
2
O( g )

2. History of the Atomic Structure. What do Atoms look like?
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Rutherford’s α-particle Experiment
- nucleus is small and
massive
- atoms are mostly open
space
Rutherford’s quote:
“It was … as if you fired a 15-inch shell at a
piece of tissue paper and it came back and hit
you.”
α-particles are very small, fast, positively
charged, and very dense. Few α-particles were
deflected and some were reflected.
“Nucleus”
“Atom”
~10
–10
m
~10
–15
m

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3. Structure of the Atom
Atomic number ( Z )
•
# of protons contained in the nucleus of a particular element
•
# of electrons = # number of protons (for a neutral atom)
•
determines atom’s characteristics
•
found on the periodic table
•
H, 1 proton; C, 6 protons.
Mass number ( A )
•
# of protons ( Z ) plus the # of neutrons ( N ): A = Z + N
•
# of neutrons varies within the same element (ISOTOPES), thus
A varies.
C
12
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This isotope of carbon is called 'carbon-12'
represents carbon
Z : carbon contains 6 protons
A = mass number
N = A – Z = 12 – 6 =
6 neutrons

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Example #1
Na
23
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Problem :
Identify the mass number, atomic number, number of protons,
number of neutrons, and the number of electrons.