Atoms and the Periodic Table
Physical Science
Chapter 4
Section 1:
Atomic Structure Objectives
• Explain Dalton’s atomic theory, and describe
why it was more successful than Democritus’s
theory.
• State the charge, mass, and location of each
part of an atom according to the modern model
of the atom.
• Compare and contrast Bohr’s model with the
modern model of the atom.
What is an atom?
An atom is the smallest unit of an element that
maintains the properties of that element.
The word atom is derived from the Greek word
meaning “unable to be divided.”
Atoms are all around us… in the air you are
breathing, in our chairs, even in our food!
How were atoms discovered?
In the fourth century BC, a Greek philosopher,
Democritus, suggested that the universe was made
of invisible units called atoms.
He thought that the movement of atoms caused the
changes in matter that he observed.
Democritus tried and tried to prove his theory but
was unable to provide evidence needed to convince
people that atoms even existed!
How were atoms discovered?
John Dalton developed his own atomic theory in
1808.
Dalton’s Atomic Theory:
• Stated that atoms could not be divided into
smaller parts
• Stated that all atoms of a given element were
exactly alike
• Stated that different elements could join
together to form compounds
Dalton’s Theory is considered the foundation for the
modern atomic theory.
Parts of an Atom
• Nucleus: small, dense center of an atom that has a
positive electric charge
• Made of protons (positive charge) and neutrons (neutral
charge)
• Protons and neutrons are almost identical in size and in
mass
• Electrons move around outside of the nucleus in
energy levels and orbitals.
• Electrons have a negative charge and are smaller than
protons or neutrons
• Electrons are constantly on the move but do remain in
predictable energy levels
Atoms and their Charges
• Atoms have an overall neutral charge
• Atoms are made of an equal number of protons (positive
charge) and electrons (negative charge)
• The number of neutrons (neutral charge) can change and
not effect the overall charge on the atom
Models of the Atom
• In 1913, Niels Bohr suggested that
electrons in an atom move in set paths
around the nucleus
• The electron’s path determines the
electron’s energy level
• Electrons can only move in certain energy levels.
They must gain or lose energy to move from one
energy level to another.
Bohr Model of a Lithium Atom
Bohr Model v. Modern Model
• In 1925, Bohr’s Model of the atom no
longer explained electron behavior.
• In the Bohr Model, electrons travel
around the nucleus the way that planets
orbit the sun in our solar system.
• In the modern model of the atom,
electrons are believed to behave
more like waves on a vibrating string.
Electron Energy Levels
• Within the atom, electrons with
different amounts of energy exist in
different energy levels.
• The number of filled energy levels depends
on the number of electrons in the atom
• First Energy Level: Holds 2 Electrons
• Second Energy Level: Holds 8 Electrons
• Third Energy Level: Holds 18 Electrons
• Fourth Energy Level: Holds 32 Electrons
Electron Orbitals
• Electron Orbitals: the regions in an atom
where electrons are likely to be found
• Four different kinds of orbitals:
•
•
•
•
s-orbital
p-orbital
d-orbital
f-orbital
Valence Electrons
• Valence Electrons: electrons that are
found in the outermost energy level
• Valence electrons are involved in
chemical bonding
• Every atom has between one and
eight valence electrons
• Noble gases have eight valence
electrons and, therefore, are stable
H
He
O
Cl
N
Na
Let’s
Let’s Practice
Practice
“Drawing
Atoms”
“Drawing Atoms”
Section 2 Objectives:
A Guided Tour of the Periodic Table
• Relate the organization of the periodic
table to the arrangement of electrons
within an atom.
• Explain why some atoms gain or lose
electrons to form ions.
• Determine how many protons, neutrons, and
electrons an atom has, given its’ symbol,
atomic number, and mass number
• Describe how the abundance of isotopes
affects an element’s average atomic mass.
Organization of the Periodic Table
• The periodic table groups similar
elements together
• Makes it easier to predict the properties of
an element based on placement
• The order is based on the number of protons
an atom of the element has in its’ nucleus
• The periodic law states that the repeating
chemical and physical properties of elements
change periodically with the atomic numbers
of the elements
Periodic Table Arrangement
• Horizontal rows in the periodic table
are called periods.
• The number of protons and the number
of electrons increase as you move leftto-right across a period.
• You can determine how the atom’s
electrons are arranged as you move
across a period.
Periodic Table Arrangement
• Vertical columns in the periodic table
are called groups.
• Atoms of the same group have the same
number of valence (outermost) electrons
and react in a similar way.
• Atoms of the same group also have
similar chemical properties.
Forming Ions
• An ion is an atom or a group of atoms
that have a net electrical charge.
• Neutral atoms form ions by gaining or
losing electrons.
• By using the groups in the periodic
table, you can predict whether an
atom will gain or lose an electron!
Example: Li atom
• Lithium is found in Group 1.
• This means that there is ONE valence
electron in the outer shell.
Li
Li
Li loses one electron
Lithium Atom:
Lithium Ion:
One valence electron
More positive now that
electron is lost
+
Example: F atom
• Fluorine is found in Group 17.
• This means that there are SEVEN
valence electrons in the outer shell.
-
F
F
F gains one electron
Fluorine Atom:
Fluoride Ion:
Seven valence electrons
More negative now that
electron is gained
Periodic Table Information
Atomic Number
Element Symbol
Element Name
Atomic Mass Number
Atomic Number: How many protons are
in the nucleus of the atom
Atomic Mass Number: How many
protons and neutrons are in the nucleus
of the atom
Let’s Do Some Math!
• How many protons
does the atom have?
• How many electrons
does the atom have?
20
Ca
40.078
• How many neutrons does the atom have?
Parts of the Nucleus
Isotopes & Avg. Atomic Mass
• An isotope is an atom that has the
same number of protons as other
atoms of the same element but have a
different number of neutrons.
• The average atomic mass for an
element is a weighted average that
includes all the element’s isotopes.
• Average atomic mass = amu (units)
Isotopes of Chlorine
The Atom
Concept Map
Section 3 Objectives:
Families of Elements
• Locate alkali metals, alkaline-earth
metals, and transition metals in the
periodic table.
• Locate semiconductors, halogens, and
noble gases in the periodic table.
• Relate an element’s chemical
properties to the electron
arrangement of its atoms.
Elements: 3 Basic Groups
• Metals:
• Shiny solids that can be stretched and
shaped
• Good conductors of heat & electricity
• Nonmetals:
• May be solids, liquids, or gases
• Dull and brittle
• Poor conductors of heat & electricity
• Semiconductors or Metalloids:
• Under certain conditions, some
nonmetals can conduct heat & electricity
Elements: 3 Basic Groups
Metal-Type Classification
• Alkali Metals: Group 1
• Reacts easily because of ONE valence
electron
• Usually not found in nature alone because
of reactivity—found in compounds
• Examples:
• Na
•K
• Li
Sodium
Potassium
Lithium
Metal-Type Classification
• Alkaline-Earth Metals: Group 2
• Have TWO valence electrons
• Less reactive than alkali metals
• Form important compounds in living
things
• Shells and bone (calcium compounds)
• Enzymes (magnesium compounds)
• Examples:
• Mg
• Ca
• Ba
Magnesium
Calcium
Barium
Metal-Type Classification
• Transition Metals: Groups 3-12
• Have different numbers of valence
electrons
• Can form both cations and anions
• Cations: positively charged ions (lose e-)
• Anions: negatively charged ions (gain e-)
• Properties of transition metals change
across a period
• Examples:
• Au
• Ag
• Hg
Gold
Silver
Mercury
Nonmetals
• Found on the right side of the periodic
table (includes H)
• Generally have 4 or more valence electrons
• Form anions easily (gain e-)
• Nonmetal compounds are plentiful on earth
• Carbon is a common nonmetal and is found
in all living things
Types of Nonmetals
• Halogens: Group 17
• Have SEVEN valence electrons
• Form –1 anions easily (gain 1 electron)
• Highly reactive elements
• Examples:
Fluorine
•F
• Cl
Chlorine
• Br
Bromine
Types of Nonmetals
• Noble Gases: Group 18
• Have EIGHT valence electrons
• Do NOT react with other elements
• Also known as inert gases
• Examples:
Neon
• Ne
• He
Helium
• Kr
Krypton
Synthetic Elements
• Synthetic elements are man-made.
• Elements with atomic numbers greater
than 92 are man-made.
• Most are radioactive
• Radioactive: decaying into other
elements
• Found in the last two periods at the
bottom of the periodic table
Section 4 Objectives
Using Moles to Count Atoms
• Explain the relationship between a
mole of a substance and Avogadro’s
Number.
• Find the molar mass of an element by
using the periodic table.
• Solve problems converting the amount
of an element in moles to its mass in
grams and vice versa.
Bell
Ringer:
Chapter 4
Section 4
What is a mole anyway??
• It’s not really a furry
creature but a way to
count in chemistry!
• Just like:
12 eggs = 1 dozen;
One mole of a substance =
23
6.022 x 10 atoms!
Avogadro’s Constant
• Chemists use large amounts of very
small particles and needed a way to
count them.
• Avogadro’s Constant, named after
Italian scientist, Amedeo Avogadro,
defines the number of atoms in ONE
mole of a substance.
23
• One mole = 6.022 x 10 atoms!
• A mole is abbreviated : 1 mol
Why such a weird number?
• Since carbon-12 is found in abundance on
earth,
• The mole is defined as the number of atoms in
12.00 grams of carbon-12.
23
• There are 6.022 x 10 atoms of carbon-12
in 12.00 grams.
• There is a relationship between atoms and
grams!
Moles and Grams are Related
• The mass in grams of 1 mol of a
substance is called its molar mass.
• The molar mass (g) is the same as the
average atomic mass (amu) listed on
the periodic table.
• We can use conversion factors to
convert:
• To moles from grams
• To grams from moles
Gumball Example p. 132
• Given : 10 gumballs has a mass of
21.4 g
• Question: What is the mass of 50
gumballs?
• How to solve:
Conversion Factor:
Given:
50 Gumballs
X
21.4 g
10 Gumballs
Arrange so that
Gumballs Cancel
=
107 g
Practice These!
1. What is the mass of exactly 150
gumballs?
2. If you want 50 eggs, how many
dozens must you buy? How many
extra eggs will you have leftover?
3. If a football player is tackled 1.7 ft
short of the end zone, how many
more yards does the team need to
get a touchdown?
Moles to Mass Problem
• Determine the mass in grams of 5.50
mol of iron.
Given:
5.50 mol Fe
Conversion Factor:
X
55.85 grams
1 mol Fe
Molar Mass From
Periodic Table
=
307 g Fe
Mass to Moles Problem
Determine the amount of Iron present
in 352 grams.
Given:
352 grams Fe X
Conversion Factor:
1 mol Fe
55.85 grams Fe
Molar Mass From Periodic Table
=
6.30 mol Fe
Graphic Organizer
1 mol
X
Molar Mass
=
Number
Of
Mass
Moles
in Grams
=
Molar Mass
1 Mol
X
Practice Problems
• Moles to Mass
• P. 133 (# 1-4); P. 134 (# 6)
• Mass to Moles
• P. 134 (# 7-9)