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UNIT 2: ATOMIC
STRUCTURE
C H E M I S T RY 1 - 2
MR. CHUMBLEY
ORIGIN OF THE
ATOM
CHAPTER 3 SECTION 1
E Q : H O W H A S T H E F U N D A M E N TA L
I D E A O F M AT T E R C H A N G E D O V E R
TIME?
THE ORIGIN OF THE ATOM
• Humans have thought about the existence of matter for a very long time
• In ancient Greece, two competing ideas for how matter exists rose to
prominence
• The word “atom” comes from the ancient Greek words, “a-” and “-tomos”
• This translates to “uncuttables”
DEMOCRITUS’ PARTICLE
THEORY OF MATTER
• Around 400 BC, a Greek philosopher named Democritus is credited
for creating the first model of the atom
• While Democritus did not come up with the idea himself, he made it
a fuller idea
• According to Democritus, “the universe is composed of two elements:
the atoms and the void in which they exist and move.”
ARISTOTLE’S CONTINUOUS
THEORY OF MATTER
• After Democritus’s time, other Greek philosophers came to support
a different idea
• According to Aristotle, matter was continuous and could be broken
down indefinitely
• Aristotle’s idea were more widely accepted as the way in which
matter existed, and his opinion was accepted for nearly 2000 years
UNDERSTANDING HOW
MATTER BEHAVES
• By the late 1700’s, most chemists knew and agreed about elements
• However, they had difficulty explaining how different substances could
combine with one another to form new ones
• This is the origin of modern chemistry, which focused on quantitative
analysis of chemical reactions
LAW OF CONSERVATION OF
MASS
• With the help of improved balances and careful measuring, the first
law was discovered
• The law of conservation of mass states that matter is neither
created nor destroyed during ordinary chemical reactions or physical
changes
LAW OF DEFINITE
PROPORTIONS
• The second discovery was that pure substances have a fixed
proportion, regardless of how it is made
• 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 the source of the compound
LAW OF MULTIPLE
PROPORTIONS
• Early chemists also knew that the same elements could combine to
create different compounds
• 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 masses of the second element combined with a certain mass of
the first element is always a ratio of small whole numbers
DALTON’S ATOMIC THEORY
• In 1808 John Dalton proposed an explanation that included all three laws
• Dalton’s atomic theory has five points:
– All matter is composed of extremely small particles called atoms.
– Atoms of an element are identical in size, mass and other properties; atoms
of different elements differ in size, mass, and other properties.
– Atoms cannot be subdivided, created, or destroyed.
– Atoms of different elements combine in simple whole-number ratios to form
chemical compounds.
– In chemical reactions, atoms are combined, separated, or rearranged.
DEMOCRITUS TO DALTON
• By using the measurable property of mass, Democritus’s idea was
made into Dalton’s scientific theory
• While we have since learned that not all points of Dalton’s theory
hold true, his basic theory has not been discarded, merely modified
and improved
COUNTING
ATOMS
CHAPTER 3 SECTION 3
E Q : H OW C A N P R OTO N S , N E U T R O N S ,
A N D E L E C T R O N S B E U S E D TO
I D E N T I F Y AT O M S ?
ATOMIC NUMBER
• All atoms of an element have the same number of protons
• The atomic number of an element is the number of protons of each
atom of that element
• Atomic number is noted by the letter Z
• In a neutral atom, the number of electrons is equal to the number of
protons
ISOTOPES
• Atoms of the same element can have different number of neutrons
• Isotopes are atoms of the same element that have different masses
• Therefore isotopes are atoms with the same number of protons, but
different numbers of neutrons
• Nuclide is a general term for a specific isotope of an element
MASS NUMBER
• Since both protons and neutrons contribute to the mass of the atom,
we can find the mass by adding the number of protons to the number
of neutrons
• The mass number is the total number of protons and neutrons that
make up the nucleus of an isotope
• Mass number is noted by the letter A
IDENTIFYING ISOTOPES
• Isotopes can be identified using hyphen notation that combines the
name of the element and the mass number
• For example:
– uranium-238
– carbon-12
– hydrogen-3
IDENTIFYING ISOTOPES
• Isotopes can be identified using the nuclear symbol, which combines the atom’s
chemical symbol (X), mass number (A), and atomic number (Z) like so:
𝐴
𝑍𝑋
• For example:
– 238
92𝑈
– 126𝐶
– 31𝐻
SAMPLE PROBLEM A
HOW MANY PROTONS, ELECTRONS, AND NEUTRONS ARE
THERE IN AN ATOM OF CHLORINE -37?
• Step 1: Analyze
– Given: name and mass number of chlorine-37
– Unknown: numbers of protons, electrons, and neutrons
• Step 2: Plan
– Atomic number = number of protons = number of electrons
– Mass number = number of protons + number of neutrons
SAMPLE PROBLEM A
HOW MANY PROTONS, ELECTRONS, AND NEUTRONS ARE
THERE IN AN ATOM OF CHLORINE -37?
• Step 3: Solve
– The mass number of chlorine-37 is 37. Using the periodic table shows the atomic
number of chlorine is 17.
Atomic number = number of protons = number of electrons
= 17 protons and electrons
Number of neutrons = mass number – atomic number
= 37 – 17 = 20 neutrons
• An atom of chlorine-37 is made up of 17 electrons, 17 protons, and 20 neutrons
HOMEWORK
• Chapter 3, Section 3
– Practice (p.76) #1-3
– Chapter Review (p.86) #8, 11
ATOMIC MASS
•
When the mass of a single atom is expressed in kilograms, the value is very small
•
For most calculations it is much easier to use a relative atomic mass
•
One unified atomic mass unit, or 1 u, is exactly 1/12 the mass of a carbon-12 atom
•
Careful calculation of the masses of different isotopes has shown that it differs slightly from the mass
number
•
The difference is due to a few factors
–
Protons and neutrons deviate slightly from 1 u
–
The mass of electrons is included in the atomic mass
–
A small amount of mass is changed into energy when proton and neutrons combine to form the nucleus
AVERAGE ATOMIC MASS
Isotope
Mass #
Abundance
Atomic
Mass (u)
• Since most elements occur naturally
as isotopes, the mass of that
element is determined by the
weighted average of those isotopes
Copper-63
63
69.15%
62.929601
Copper-65
65
30.85%
64.927794
• Average atomic mass is the
weighted average of the atomic
masses of the naturally occurring
isotopes of an element
Average atomic mass calculation:
• The weighting of the mass values is
determined by the percentage that
isotope has in natural abundance
+
0.6915 × 62.929 601 u
0.3085 × 64.927 794 u
63.55 u
A NEW ATOMIC
MODEL
CHAPTER 4 SECTION 1
E Q : H OW H A S T H E M O D E L O F T H E
AT O M C H A N G E D W I T H T H E
D I S C O V E R Y O F S U B AT O M I C
PA R T I C L E S ?
MODELS OF THE ATOM
• Historically, the model of the atom has changed over time
• In the early 20th century, a new model of the atom developed with
better understanding of light, waves, and atomic particles
• This led to the quantum model of the atom
LIGHT
• Light, is a generic term for any kind of electromagnetic radiation
• Electromagnetic radiation is a form of energy that exhibits wavelike
behavior as it travels through space
• The electromagnetic spectrum is comprised of all forms of
electromagnetic radiation
THE ELECTROMAGNETIC
SPECTRUM
BOHR’S MODEL
• In 1913, Danish physicist Niels
Bohr proposed that electrons
can only exist in specific orbits
around the nucleus of an atom
• While in a given orbit, an
electron neither gains nor
loses energy
BOHR’S MODEL
• Emission is the process by which an electron falls to a lower energy
state, and releases a photon
• Absorption is the process by which a photon adds energy to increase
the energy state of an electron
EXCITED ELECTRONS
GOING TO EXCITED
STATE
GOING TO GROUND
STATE
EMISSION SPECTRUMS
HYDROGEN SPECTRA
QUANTUM MODEL OF THE
ATOM
• Additional information has led to a refining of Bohr’s model of the
atom
• Careful study of the nature of electrons around atoms led to a change
in the way atoms are viewed
• Quantum theory describes the wave properties of electrons and
other very small particles
MODELS OF THE ATOM
BOHR’S MODEL
(PLANETARY MODEL)
QUANTUM MODEL
HOMEWORK!
• Briefly describe what you understand about how the model of the
atom changed due to gain of knowledge about light and particles.
HISTORY OF THE PERIODIC
TABLE
CHAPTER 5 – SECTION 1
E Q : H O W W A S T H E P E R I O D I C TA B L E
DEVELOPED?
DEVELOPING THE PERIODIC
TABLE
• By the mid 1800’s, over 60 elements has been discovered and identified
• Chemists at this time, primarily examined the properties of known elements and
compounds containing known elements
• In September of 1860, the First International Congress of Chemists was assembled in
Karlruhe, Germany to establish standards for determining atomic mass
• Italian chemist Stanislao Cannizzaro presented a method to accurately measure relative
masses of atoms
• This method led to standard values for atomic mass
MENDELEEV’S PERIODIC
TABLE
• Russian Chemist Dmitri Mendeleev wanted to
organize the known elements by their properties
• Mendeleev noticed that when elements were
organized by atomic mass, certain properties appeared
at regular intervals
• These repeating patterns are considered periodic
MENDELEEV’S PERIODIC
TABLE
• Mendeleev’s table grouped elements with
similar properties
• Mendeleev left many gaps in his periodic
table, anticipating that there were
undiscovered elements
ATOMIC NUMBER
• Mendeleev’s Table was very useful, but left two questions unansered:
– Why could most elements be arranged in order of increasing atomic mass, but not all?
– What was the reason for chemical periodicity?
• In 1911, English scientist Henry Mosley was examining the emission spectra of
many different metals
• Mosley noticed that elemental properties aligned better together when they were
arranged by atomic number
• The periodic law states that the repeating chemical and physical properties of
elements change periodically with the atomic numbers of the elements
MODERN PERIODIC TABLES
• Modern periodic tables arrange elements by both atomic number and
chemical properties
• The periodic table is an arrangement of the elements in order of their
atomic numbers so that elements with similar properties fall in the same
group
• The vertical columns of elements the periodic table are called groups or
families
• The horizontal rows of elements in the periodic table are called periods
NOTABLE GROUPS
• Noble Gases
– Between 1894 and 1900, all the noble gasses were discovered by a variety of scientists
– These elements had been previously undiscovered since they are totally unreactive
• Lanthanides are the 14 elements with atomic numbers from 58 (cerium) to 71
(lutetium)
• Actinides are the 14 elements with atomic numbers from 90 (thorium) to 103
(lawrencium)
• Elements in the lanthanides and actinides have very similar properties to each
other , but were very difficult to identify and place into the periodic table
MAJOR GROUPS OF THE PERIODIC
TA B L E
Alkali Metals
Alkaline Earth
Metals
Transition Metals
Post-Transition
Metals
Metaloids
Non-Metals
Halogens
Noble Gases
Lanthinides
Actinides
MAJOR GROUPS OF THE
PERIODIC TABLE
•
Alkali Metals
–
•
Alkaline Earth Metals
–
•
Group 18
Lanthinides
–
•
Most of the remaining elements to the right of metalloids
Noble Gases
–
•
Specific metals between metals and non-metals moving diagonally from the top of group 13 to the bottom of group 17
Non-Metals
–
•
Groups 3-12, with additional metals in groups 13-16
Metaloids
–
•
Group 2
Transition Metals
–
•
Group 1
Top row of elements removed from period 6
Actinides
–
Bottom row of elements removed from period 7
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ELECTRON
C O N F I G U R AT I O N S
CHAPTER 5 SECTION 2
E Q : H O W D O E S T H E P E R I O D I C TA B L E
I N D I C AT E T H E L O C AT I O N O F T H E
E L E C T R O N S A R O U N D T H E AT O M ?
ENERGY LEVELS AND
ORBITALS
• We have previously discussed how electrons exist within specific
energy levels around the nucleus of an atom
• In addition to energy levels, electrons are located in what are called
orbitals
• The orbitals are described as s, p, d, and f
• As both the energy level and orbitals increase, so does the complexity
of the shape
• Valence electrons are found in the outermost shell of an atom and
determine its chemical properties
SHAPE OF ORBITALS
(P. 103 IN TEXTBOOK)
ELECTRON CONFIGURATION
• The arrangement of electrons in an atom is known as the electron
configuration
• The electron configuration for individual elements helps indicate
certain properties
• Additionally, elements within the same period have the same electron
configuration
ELECTRON CONFIGURATION
AND THE PERIODIC TABLE
BELLRINGER!
p. 141 Formative Assessment #1-2
1.
To illustrate the relationship between the element’s electron
configurations and their placement in the periodic table, into what
four blocks can the periodic table be divided?
2.
What is the name given to each of the following groups in the
periodic table?
a.
Group 1
b.
Group 2
c.
Groups 3-12
d.
Group 17
e.
Group 18