Chapter 3 - Atoms: the building blocks of matter

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Chapter 3 - Atoms the building blocks of matter

• Taken from Modern Chemistry written by Davis,
  Metcalfe, Williams Castka

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Section 3.1 The Atom from philosophical idea
to scientific theory

• Objectives

HW Notes on section 3.1 pgs 65-67

• Students will be able to
• Explain the laws of
• Conservation of mass
• Definite proportion
• Multiple proportion
• Summarize the 5 essential points of Daltons
  atomic theory
• Explain the relationship between the 5 essential
  points and the above mentioned laws

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Section 3.1 The Atom from philosophical idea
to scientific theory

• Foundations of Atomic Theory

As early as 400 B.C.E. particle theory of matter
was supported the particle was called an atom
based on the Greek for indivisible. Supported
by Democritus Aristotle did not believe this
theory and his opinion lasted for 2 000 years.
Felt all matter was continuous.
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Section 3.1 The Atom from philosophical idea
to scientific theory

• Foundations of Atomic Theory (continued)

By 1700s accepted idea that an element could not
be broken down further. Back
The transformation of substance or substances
into one or more new substances was known as a
chemical reaction.
By the 1790s there was a new emphasis on
quantitative analysis of chemical reactions
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Section 3.1 The Atom from philosophical idea
to scientific theory

• Foundations of Atomic Theory (continued)

This work lead to the discovery of several laws.
. .
Law of Conservation of matter which states that
mass is neither destroyed or created during
ordinary chemical or physical reactions.
Back
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Section 3.1 The Atom from philosophical idea
to scientific theory

• Foundations of Atomic Theory (continued)

The law of definite proportions, sometimes called
Proust's Law, states that a chemical compound
always contains exactly the same proportion of
elements by mass.
Book example salt is always 39.34 Na (sodium)
and 60.66 Cl (Chlorine) by mass
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Section 3.1 The Atom from philosophical idea
to scientific theory

• Foundations of Atomic Theory (continued)

The law of multiple proportions, statement that
when two elements combine with each other to form
more than one compound, the weights of one
element that combine with a fixed weight of the
other are in a ratio of small whole numbers.
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Section 3.1 The Atom from philosophical idea
to scientific theory

• Daltons Atomic Theory

1.All matter is made of extremely small particles
called atoms. Relationship
2.All atoms of the same element are identical in
size, mass other properties. Relationship
3.Atoms cannot be subdivided, created or
destroyed. Relationship
4.Atoms of different elements combine in
WHOLE-number ratios to form compounds.
5.In chemical reactions atoms are combined,
separated or rearranged. Relationship
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Section 3.1 The Atom from philosophical idea
to scientific theory

• Modern Atomic Theory

Dalton turned ideas (of ancient Greeks) into
scientific theory
Today we know that atoms can be divided, but the
law of conservation of matter holds true still.
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Section 3.1 The Atom from philosophical idea
to scientific theory

• Quiz Break

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Section 3.2 The Structure of the Atom

• Objectives

HW Notes on section 3.2 pgs 70-74

• Students will be able to
• Summarize the observed properties of cathode
  rays that led to the discovery of the electron.
• Summarize the experiment carried out by
  Rutherford and his co-workers that led to the
  discovery of the nucleus.
• List the properties of protons, neutron and
  electrons
• Define atom.

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Section 3.2 The Structure of the Atom

• Discovery of the Electron

1st discovery of a subatomic particle resulted
from investigations into the relationship between
electricity and matter.
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Section 3.2 The Structure of the Atom

• Discovery of the Electron - Cathode Rays and
  Electrons

Hypothesized that the glow was caused by a stream
of particles which they called a cathode ray.

• Tested and found that
• An object placed between the cathode ray and the
  opposite end casts a shadow.
• A paddle wheel placed on rails rolled toward the
  anode from the cathode.

Dont forget hyperlink
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Section 3.2 The Structure of the Atom

• Discovery of the Electron - Cathode Rays and
  Electrons (continued)

This supported the idea of a cathode ray. . .

• Further testing found that
• Cathode rays were deflected by a magnetic field.
• Deflected away from negatively charged objects.

Thompson hypothesized that the ray was a
particle, a negative one later named electrons.
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Section 3.2 The Structure of the Atom

• Charge and Mass of the electrons

Thompsons work showed that the electron has a
very large charge for its tiny mass
R. A. Millikan (right) showed the mass to be
9.109 x 10-31 kg
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Section 3.2 The Structure of the Atom

• Charge and Mass of the electrons (continued)

Based on that information two more inferences
were made about atomic structure.

• Atoms are electrically neutral so there must be
  positively charged particles to balance out the
  negative electron.
• Because electrons have so much less mass than
  atoms, atoms must contain other particles which
  account for most of their mass.

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Section 3.2 The Structure of the Atom

• Discovery of the Atomic Nucleus

Ernest Rutherford associates bombarded a thin
gold foil with alpha particles ( charge 4 x
mass of H atom) Expected most particles to pass
through with slight deflection shocked to find
that 1 in 8 000 were redirected back toward
source.
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Section 3.2 The Structure of the Atom

• Discovery of the Atomic Nucleus (continued)

Rutherford reasoned that the bounce back was from
a densely packed bundle with a positively bundle
he called the nucleus.
If the nucleus were the size of a marble the atom
would be the size of a football field
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Section 3.2 The Structure of the Atom

• Composition of the Atomic Nucleus

Except for the simplest type of hydrogen all
atomic nuclei are made of two types of particles,
protons and neutrons.
Protons have a () charge which balances out the
charge of the electrons. Mass 1.673 x 10-27 kg
Neutrons have a no charge and a mass 1.675 x
10-27 kg
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Section 3.2 The Structure of the Atom

• Composition of the Atomic Nucleus (continued)

Nuclei of atoms of different elements differ in
the of protons they contain and therefore in
the amount of positive charge.
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Section 3.2 The Structure of the Atom

• Properties Summarized

Particle Symbols Relative electric charge Mass number Relative Mass (amu) Actual mass (kg)
Electron e-, -1 0 0.000 5486 9.109 x 10-31
Proton p, 1 1 1.007 276 1.673 x 10-27
Neutron no, 0 1 1.008 665 1.675 x 10-27
1 amu (atomic mass unit) 1.660 540 x 10-27 kg
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Section 3.2 The Structure of the Atom

• Composition of the Atomic Nucleus - Forces in the
  Nucleus

Like forces generally repel one another however
when two protons are extremely close there is a
strong attractions
These short-range proton-neutron, proton-proton,
and neutron-neutron forces hold the particles
together and a referred to as nuclear forces.
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Section 3.2 The Structure of the Atom

• The sizes of Atoms

Atomic radii range from 40 to 270 pm
(picometers) Where as the nuclei of atoms have a
much smaller radii About 0.001 pm
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Section 3.3(A) Counting Atoms

• Objectives

HW Notes on section 3.3 pgs 75-80

• Students will be able to
• Explain what isotopes are.
• Define atomic number and mass number, and
  describe how they apply to isotopes.
• Given the identity nuclide, determine its number
  of protons, neutrons and electrons.

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Section 3.3(A) Counting Atoms

• Atomic Number

The atomic number of an element is the number of
protons in the nucleus of each atom of that
element

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Section 3.3(A) Counting Atoms

• Isotopes

Isotopes are atoms of the same element that have
different masses. All hydrogen contain the
same number of protons but may contain different
number of neutrons.

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Section 3.3(A) Counting Atoms

• Mass Number

The mass number is the total number of protons
and neutrons in the nucleus of an isotope.

Mass Number 1 2 3
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Section 3.3(A) Counting Atoms

• Isotopes - pogil

Isotopes Are all atoms of an element alike?
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Section 3.3(A) Counting Atoms

• Isotopes Pennium Lab

Isotopes of Pennium
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Section 3.3(A) Counting Atoms

• Designating Isotopes

Nuclide is a general term for any isotope of any
element.

S elements symbol
Nuclear Symbol
a protons neutrons
b protons
Protons ______ Neutrons _______ Electrons
________
Bromine has
Practice
Practice Key
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Section 3.3(A) Counting Atoms

• Relative Atomic Masses

The standard used by scientist to govern units of
atomic mass is the carbon-12 nuclide. One atomic
mass unit , or amu is exactly 1/12th the mass of
a carbon-12 atom, or 1.660 540 x 10-27 kg
Although isotopes may have different masses,
they do not differ significantly in their
chemical behavior.

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Section 3.3(A) Counting Atoms

• Average Atomic Masses of Elements

Average atomic mass is the weighted average of
the atomic masses of the naturally occurring
elements.

Example with marbles (100 total) 25 marbles x
2.00 g 50 g 75 marbles x 3.00 g 225 g Adding
the masses gives 50 g 225 g 275 g Divide
this by the total number of marbles and you get
an average marble mass of 2.75 g
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Section 3.3(A) Counting Atoms

• Average Atomic Masses of Elements (continued)

Average atomic mass How are the masses on the
periodic table determined?
(KEY)
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Section 3.3(B) Counting Atoms

• Objectives

HW Notes on section 3.3 pgs 80-85

• Students will be able to
• Define mole in terms of Avogadros number, and
  define molar mass.
• Solve problems involving mass in grams, amount in
  moles and number of atoms of an element.

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Section 3.3(B) Counting Atoms

• Relating Mass to Numbers of Atoms - the Mole

A mole (abbreviated mol)is the amount of a
substance that contains as many particles as
there are atoms in exactly 12 g of carbon-12.

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Section 3.3(B) Counting Atoms

• Relating Mass to Numbers of Atoms Avogadros
  number

The number of particles in a mole has been
experimentally determined in a number of
ways. Avogadros number 6.011 1367 x 1023 is
the number of particles in exactly one mole of a
pure substance. For ours (and most purposes)
Avogadros number is rounded to 6.022 x 1023

It is a big number!
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Section 3.3(B) Counting Atoms

• Relating Mass to Numbers of Atoms Molar Mass

The alternative definition of mole is the amount
of substance that contains avogadros number of
particles. The mass of one mole of a pure
substance is called the molar mass of that
substance. Usually written in units of g/mol.

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Section 3.3(B) Counting Atoms

• Relating Mass to Numbers of Atoms Gram/Mole
  Conversions

There are 3 mole equalities. They are 1 mol
6.02 x 1023 particles 1 mol g-formula-mass
(periodic table) 1 mol 22.4 L for a gas at STP
STP 0 C 1 atm Pressure
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Section 3.3(B) Counting Atoms

• Relating Mass to Numbers of Atoms Conversions

There are 3 mole equalities. They are 1 mol
6.02 x 1023 particles 1 mol g-formula-mass
(periodic table) 1 mol 22.4 L for a gas at STP

These become. . .
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Reference Sheet
There are 3 mole equalities. They are 1 mol
6.02 x 1023 particles 1 mol g-formula-mass
(periodic table) 1 mol 22.4 L for a gas at STP

These become. . .
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Section 3.3(A) Counting Atoms

• Relating Mass to Numbers of Atoms What does it
  mean?

g-formula-mass (periodic table)
For a single element it is simply the atomic mass
found on the periodic chart

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Section 3.3(A) Counting Atoms

• Relating Mass to Numbers of Atoms Examples

g-formula-mass (periodic table)
N

Ca
Ag
Ba
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Section 3.3(A) Counting Atoms

• Relating Mass to Numbers of Atoms What does it
  mean?

g-formula-mass (periodic table)
For a COMPOUND you will need to calculate using
atomic mass found on the periodic chart

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Section 3.3(B) Counting Atoms

• Relating Mass to Numbers of Atoms EXAMPLE

g-formula-mass (periodic table)
COMPOUNDS

Table Salt NaCl
Water H2O
Sugar (glucose) C6H12O6
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Section 3.3(B) Counting Atoms

• Relating Mass to Numbers of Atoms EXAMPLE

g-formula-mass (periodic table)
COMPOUNDS

inorganic salt (soil fertilizer) (NH4)2SO4
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Section 3.3(B) Counting Atoms

• Relating Mass to Numbers of Atoms MOLE
  PRACTICES

Practice 1
Practice 2
Practice 2 (Key)
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Section 3.3(B) Counting Atoms

• Relating Mass to Numbers of Atoms FUN WITH
  MOLES

Given 2.860 m ? ceiling height 9.630 m ?
room depth 10.620 m ? room width

Atmosphere composition Nitrogen -
78.084Oxygen - 20.95
1 000 L 1 m3
How many mols of O2 and N2 are present in this
room?
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Section 3.3(B) Counting Atoms

• Relating Mass to Numbers of Atoms FUN WITH
  MOLES

Average lung volumes in healthy adults7 Average lung volumes in healthy adults7 Average lung volumes in healthy adults7
Volume Value (litres) Value (litres)
Volume In men In women
Inspiratory reserve volume 3.3 1.9
Tidal volume 0.5 0.5
Expiratory reserve volume 1.0 0.7
Residual volume 1.2 1.1
Atmosphere composition Nitrogen -
78.084Oxygen - 20.95

How many particles of O2 and N2 are taken in with
each breath?
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Section 3.3(B) Counting Atoms

• Relating Mass to Numbers of Atoms suggestions

1. Relax
2. Look for things you recognize
3. Estimate size of final answer (with this comes
   do I remember using any of these before)
4. Set up and work out
5. Double check with estimate and your sig figs

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Section 3.3(B) Counting Atoms

• Relating Mass to Numbers of Atoms MORE MOLE
  PRACTICES

Practice 3
Practice 3 (KEY)

TAKE-HOME QUIZ (KEY)
TAKE-HOME QUIZ
Practice 4
Practice 4 (KEY)
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Section 3.3(B) Counting Atoms

• Relating Mass to Numbers of Atoms Q - 4

Want to get to Mols...

100 atoms Ar
? 1 x 102 atoms Ar
1 x 102 atoms Ar
1 mol
-------------------------
X -------------------------
1
6.02 x 1023 particles
0.166 x 10-21 particles , which is equal to 1.66
x 10-1 x 10-21
Or more properly written as 1.66 x 10-22 mols Ar