The “Chemystery”
of Chemistry!
Meet the
“Atoms Family”
Academic Chemistry
Chapter 3
Objectives 3.2
•Explain the relationship between the laws of conservation of
mass, definite proportions, and multiple proportions.
•List the properties of protons, neutrons, and electrons.
•Define the atom.
•Use the atomic number and mass number to determine the
numbers of subatomic particles present in an atom.
•Explain what isotopes are.
•Define atomic number and mass number, and describe how
they apply to isotopes.
•Given the identity of a nuclide, determine its number of
protons, neutrons, and electrons.
The Structure of an Atom
•During the 1700s and1800s scientists
experimented to determine what the
structure of an atom was.
•Today’s definition of an atom is the
smallest particle of an element that
retains the chemical properties of that
element.
The Structure of an Atom
•The study of matter was revolutionized in
the 1790s by a new emphasis on the
quantitative analysis of chemical
reactions.
•Aided by improved balances, scientists
were able to accurately measure the
masses of the elements and compounds
which led to the discovery of several basic
laws.
The Structure of an Atom
•The law of conservation of mass states
that matter is neither created nor
destroyed during ordinary chemical
reactions or physical changes.
The Structure of an Atom
•The law of definite proportions states that a chemical
compound contains the same elements in exactly
the same proportions by mass regardless of the size of
the sample or source of the compound.
The Structure of an Atom
•The law of multiple proportions states that if two or
more different compounds are composed of the
same two elements, then the ratio of the mass of the
second element combined with a certain mass of the
first element is always a ratio of small whole numbers.
The Structure of an Atom
There are 2 parts of an
atom of an element:
The Nucleus
The Electron Cloud
Atoms consist of a
nucleus (composed of
positive protons and
neutral neutrons).
The nucleus is surrounded
by an electron cloud
(composed of negative
electrons).
•Dense central region of an
atom
•Almost completely empty
space
•Contains most of an atom’s
mass and a very small amount
of its volume.
•Contains most of an atom’s
volume and a very small
amount of its mass.
The Structure of an Atom
•Protons, Neutrons, and Electrons are all
considered Subatomic Particles.
The Structure of an Atom
•How big are atoms?
•They are measured in picometers (10-12)
•Atomic radii range from 40-270 pm, but have an
incredibly high density of 2x108 metric tons/cm3.
•How big are the subatomic particles?
The proton’s mass is 1.673 x 10-27 kg.
The neutron’s mass is 1.675 x 10-27 kg.
The electron’s mass is 9.109 x 10-31 kg.
The Structure of an Atom
The relative size of the nucleus in an atom is roughly the same as that
of a pea in the middle of this huge stadium.
Atomic Nuclei
•All atomic nuclei are made of
two kinds of subatomic particles:
1. Protons (positive charge)
2. Neutrons (neutral charge)
•
One exception is the simplest
Hydrogen atom which has
only one proton and one
electron.
Atomic Nuclei
•All atoms should be electrically neutral.
•They should contain equal numbers of
protons and electrons.
•The nuclei of different elements have
different numbers of protons.
Atomic Nuclei
•The number of protons is the same as the
atomic number on the Periodic Table of
Elements.
Atomic Number = #
protons
Hydrogen has an atomic
number of 1, so has only
1 proton.
Atomic Nuclei - Practice
Using your Periodic Table, how many protons do
the following elements have?
2 protons
•He __________
23 protons
•V ___________
•U ___________
92 protons
86 protons
•Rn __________
Atomic Nuclei
•Forces in the nucleus:
•Generally, when there are like forces
close together, they repel.
•Protons – Protons
•Electrons – Electrons
•In the nucleus protons are able to be
grouped together with other protons, as
with neutrons as well.
•These forces are known as nuclear
forces.
Counting Subatomic Particles
•Atomic Number
•All atoms of the same element have
the same number of protons.
•Symbolized by Z, the atomic number
of each element represents the
number of protons in that atom’s
nuclei.
•Because atoms are neutral, they
should have the same number of
negative electrons as well.
Counting Subatomic
Particles
•Mass Number
•Represents the total number of protons and
neutrons in an atom’s nucleus.
•The average atomic mass is found on the
periodic table.
•By subtracting the atomic number (#
protons) from the mass number (# protons +
# neutrons), the number of neutrons can be
calculated.
Counting Subatomic
Particles
Atomic
Number
(Z)
(# protons)
=
(# electrons)
Mass
Number
(A)
(# protons + # neutrons)
Counting Subatomic
Particles
Element
Atomic
Mass
Protons
Neutrons
Number
Number
Helium
2
4
Calcium
20
40
Silver
47
108
Americium
95
243
Electrons
NAME
SYMBOL
ATOMIC
NUMBER
MASS
Number of
Number
NUMBER PROTONS
of
(rounded)
NEUTRONS
Number
of
ELECTRONS
Calcium
12
24
1
0
Au
30
201
17
Bismuth
80
18
209
Xe
26
83
Meet the Atoms Family Isotopes!
•
Isotopes are atoms that have the same
number of protons and electrons, but
different numbers of neutrons.
Element
Atomic
Number
Mass
Number
Protium
1
1
Deuterium
1
2
Tritium
1
3
Protons
Neutrons
Electrons
Meet the Atoms Family Isotopes!
Protium accounts for 99.985% of the
hydrogen atoms found on Earth.
• Deuterium accounts for 0.015% of the
hydrogen atoms found on Earth.
• Tritium is prepared artificially and is
radioactive.
•
Meet the Atoms Family Isotopes!
• Some
isotopes occur naturally, or
they can be man-made in the
laboratory (artificial isotopes), like
tritium.
• The general term for an isotope of
any atom is a nuclide.
• Even though isotopes have different
numbers of neutrons, their properties
tend to be similar.
Meet the Atoms Family Isotopes!
• Most
isotopes do not have a unique
name. One method of writing their
name is known as hyphen notation.
• Tritium is also known as Hydrogen-3.
Element Mass
Name Number
Meet the Atoms Family Isotopes!
• The second type of notation is known
as an element’s nuclear symbol.
• Tritium’s nuclear symbol is:
Mass
Number
Atomic
Number
3
1
H
Element
Symbol
Meet the Atoms Family Isotopes!
• Write the hyphen notation and
nuclear symbol for an element
containing 15 electrons and 15
neutrons.
Hyphen
Notation
Phosphorus-30
Nuclear Symbol
Meet the Atoms Family Isotopes!
• Write the hyphen notation and
nuclear symbol for an element
containing 13 protons and 14
neutrons.
Hyphen
Notation
Aluminum-27
Nuclear Symbol
Element
Element
Symbol
Nuclear
Symbol
Hyphen
Notation
Atomic
Number
Mass
Number
Number
of
Protons
Nitrogen
N
14 N
7
Nitrogen14
7
14
7
22
47
9
19
80
40
1
Number of Number of
Neutrons Electrons
7
7
45
20
0
222
86
Element
Name
Card #
1
2
3
4
5
6
7
8
9
10
11
12
Nuclear
Symbol
Hyphen
Notation
Atomic
Number
Mass
Number
Number of Number of Number of
Protons
Neutrons Electrons
(pink)
(blue)
(green)
Objectives 3.3
•Distinguish between relative atomic mass and
average atomic mass.
•Calculate the average atomic mass for the isotopes
of a given element.
•Define mole in terms of Avogadro’s number, and
define molar mass.
•Solve problems involving mass in grams, amount of
moles, and number of atoms.
Relative Atomic Mass!
•
Relative atomic mass is a standard unit of
mass used to measure atoms.
•
•
•
Relative atomic mass is used because a single
atom of oxygen only weighs 2.656 x 10-23 g.
This is a standard, so it is consistent everywhere.
Scientists started with the Carbon-12 atom and
assigned it a mass of 12 amu (atomic mass
units).
• Hydrogen-1
is 1/12 the size of a Carbon-12 atom, so it
would have a relative atomic mass of 1 amu.
Average Atomic Mass!
•
The average atomic mass is the
weighted average mass of the naturally
occurring isotopes of that element.
•
•
This is the mass that is found on the periodic
table.
To calculate the average atomic mass,
one needs the
• Percentage
of each isotope of that element
that occurs in nature.
• The atomic mass of each isotope of that
element.
Average Atomic Mass!
• Calculate
the average atomic mass
of Copper.
• Naturally, Copper-63 is 69.17%
abundant and has a mass of
62.929589 amu.
• Its other isotope, Copper-65 , has
an atomic mass of 64.927793 amu
and is 30.83% abundant.
Average Atomic Mass!
Naturally occurring chlorine that is put in pools is
75.53% chlorine-35 (mass = 34.969 amu) and 24.47%
chlorine-37 (mass = 36.966 amu). Calculate the
average atomic mass.
Average Atomic Mass!
Calculate the average atomic mass for neon if its
abundance in nature is 90.5% neon-20 (19.922 amu),
0.3% neon-21 (20.994 amu), and 9.2% neon-22
(21.991 amu).
Average Atomic Mass!
•
•
Knowing the average atomic mass helps
to determine how many atoms of each
element are present in a sample.
To calculate the number of atoms, we will
be using the following concepts:
•
•
•
The mole
Avogadro’s number
The molar mass
Meet Mr. Mole!
• The
mole is the SI unit of
measurement for the
amount of a substance.
It is abbreviated mol.
• It is a quantity (6.022 x 1023
particles = 1 mol of any
substance).
•
• It
is considered a counting unit,
just like there are always 12
eggs in a dozen.
Avogadro Discovered the Mole!
Amadeo Avogadro is
credited with determining
how many atoms were
present in 12 grams of
Carbon-12.
• That number of atoms,
6.022 x 1023, is known as
Avogadro’s number and
is used to relate mass and
number of atoms.
•
Avogadro’s Number
•
How big is Avogadro’s number?
•
•
•
Imagine a box large enough to hold a mole
(6.022 x 1023) peas.
• Assume a dried pea is about a quarter inch
(6 mm) in diameter.
• The volume of a single pea is 4/3π r3 or
about 38 mm3.
If you carry the calculation to its conclusion by
multiplying the volume of a single pea by
Avogadro's number (6.022 x 1023) and then
finishing up the unit conversions, you'll discover
the box would be a little more than 200 miles
long, wide and tall.
About the length from EFHS to Harrisburg or
Buffalo, New York.
Molar Mass
• The
mass of one mole of atoms is
known as the molar mass of that
substance.
The units of molar mass are g/mol
(grams per mol).
• The molar mass is numerically equal to
the atomic mass of the element.
•
• Helium
has a molar mass of 4.00 g/mol and
an atomic mass of 4.00 amu. (This number
can be found on the periodic table.)
Molar Conversions
•
•
Chemists use molar conversions to
determine how many atoms, moles, or
grams are in a sample of a particular
substance.
The following conversion factors are
important to solving these problems:
•
•
6.022 x 1023 atoms = 1 mole
___ g = 1 mole (obtain this # from the
periodic table)
Molar Conversions
1. What is the mass in grams of 3.6
mol of the element carbon, C?
Molar Conversions
2. How many moles of copper, Cu,
are there in 3.22 g of copper?
Molar Conversions
3. How many moles of carbon, C, are
in 2.25 x 1022 atoms of carbon?
Molar Conversions
4. How many atoms of copper, Cu,
are in 3.00 moles?
Molar Conversions
5. How many atoms of carbon, C, are
in 0.020 g of carbon?
Molar Conversions
6. How many grams of oxygen, O, is
4.59 x 1030 atoms?
Molar Pencil Assignment
Vegium Lab
Isotopes Activity (Note cards)
Introduction to the Mole Activity