Transcript Chapter 5

Chapter 5
Foundations of Chemistry
Chemistry and Matter
Chemistry is:
the study of the composition of matter
(the substance of the physical world)
&
the study of the interactions of matter
with matter
Beginnings of Chemistry
Apothecaries – early chemists – they
produced perfumes, ointments, and
medicines.
Characteristics of Matter
• Matter occupies space
two pieces cannot occupy the same
space at the same time.
• Matter has inertia
the property of resisting changes in
motion.
Matter cannot be created or destroyed under
normal circumstances… it can only change form.
Characteristics of Matter
• Matter ordinarily exists in three basic
states:
1. solid – definite shape
2. liquid – assumes the shape of a
container and has
a definite volume
3. gas – has no definite shape or
volume
Characteristics of Matter
One more state of matter:
Plasma – when the temperature is
so great that matter’s ordinary states
cannot exist.
Plasma typically only exists in
stars…because so much heat is required.
Composition of Matter
The atomic theory of matter:
1. all matter consists of tiny particles called
atoms.
2. all atoms of the same element have the same
properties.
3. atoms can combine to make other
compounds.
4. elements are composed of a single type of
atom.
5. chemical processes are the result of the
rearrangement, combination, or separation of
atoms
Atomic Theory
According to atomic theory, the differences
between various kinds of matter result
from differences in their respective atoms
or in the way their atoms are combined
into molecules.
Molecule: a group of atoms linked together;
both elements and compound may be
composed of molecules.
Elements
Elements are the building blocks of all
substances in the universe.
As of 1998 chemists had identified 115
elements, of which only 88 occur naturally
in the earth; the remaining elements have
been produced in the laboratory.
Atomic Symbols
Elements have been given designated
symbols that enable scientists to
recognize them and put them into
chemical equations more easily…
Example: Cobalt is Co
Sodium is Na
Kinetic Theory of Motion
Particles in matter are in constant motion…
The rate and energy of their motion depends
upon their temperature; the higher the
temperature, the faster the molecules
move.
Diffusion
Diffusion always occurs in one
direction…from higher concentration to
lower …
Concentrated vapors spread out into less
concentrated areas…
Osmosis
Osmosis is the diffusion of water…it relates
only to the movement of water from high to
low concentration…
Nuclear Chemistry
Atomic Structures
Atoms are composed of:
Negative particles: electrons
Positive Particles: protons
Neutral Particles: neutrons
Nuclear Chemistry
Atoms Have Two Parts:
1. the nucleus
2. the orbitals
The Nucleus
The nucleus has two components:
Protons (positive)
and
Neutrons (neutral)
Orbitals
The orbitals are the
location of the fast
moving charged
particles: Electrons
Orbitals
• Orbitals are the paths the electrons follow
around the nucleus.
• They are also known as Energy Levels.
• Energy levels are a general region of
space where electrons most probably
exist.
Nuclear Chemistry
Atomic Mass
Protons and neutrons are about equal…and
electrons are disregarded because they
are so small…
Therefore,
Atomic mass is determined by adding the
masses of the protons and neutrons.
Nuclear Chemistry
Scientists don’t use kilograms with atoms,
they use a special
Atomic Mass Unit
Equal to 1/12 the mass of a carbon atom
that has 6 protons and 6 neutrons.
Thus… 1 amu is equal to the mass of 1
proton or neutron.
Nuclear Chemistry
To find the atomic mass of any atom simply
total the number of the particles in the
nucleus.
Atomic Number
The atomic number is the number of
protons in an atom of a given element.
Example: Gold
It has 79 protons in the nucleus…therefore,
79 is Gold’s atomic number.
Atomic Number
Atoms are typically electrically neutral…they
have a charge of zero!
Example: Carbon has 6 protons and
therefore, 6 electrons.
Mass Number
Mass number is the same as the atomic
mass…it is the sum of the protons and
neutrons.
If you subtract the atomic # from the mass #
you will have the # of neutrons in an atom.
Mass Number
Krypton has a mass # of 84 and an atomic number of 36.
84 – 36 = 48
Krypton has 48 neutrons in the nucleus.
Mass Number
Atoms of the same element
that have different
numbers of neutrons in
their nuclei are called
isotopes.
It is indicated by a special
notation called isotopic
notation, which shows
both the atomic number
and the mass number of
the element.
Nuclear Radiation
The emission of high-energy rays and
particles (protons and neutrons) from a
nucleus is called Radioactivity.
Most elements are not radioactive.
only elements with an atomic #
over 84 are!
3 Types of Radiation
Identity
Charge
Penetration
Alpha
Helium
Nucleus
+2
Low
Beta
Electron
-1
Medium
Gamma
Electromagnetic
radiation
0
High
Name
Symbol
Types of Radiation
• Beta Particles are
free electrons
• Gamma rays are
things like x-rays and
radio waves only with
much more energy.
Nuclear Decay
When nuclear changes occur the nuclei end
up with extra energy.
This energy is released as Gamma Rays
A meter of concrete or 2 inches of lead is
required to stop Gamma Rays.
Alpha Decay
Alpha particles are
helium nuclei.
They consist of 2
protons and 2
neutrons.
Beta Decay
The emission of an
electron from the
nucleus and the
transformation of the
atom into a different
element with the next
higher atomic # is the
result.
Nuclear Bombardment Reactions
NBRs occur when a nucleus is struck with
atomic particles or other nuclei.
In the 1930’s scientists discovered they
could make a nucleus unstable by striking
it with a nucleus.
Nuclear Bombardment Reactions
Stars are huge fusion
reactors.
Fusion reactors are
safer than fission
reactors, but require
such extreme
temperatures that we
have not been
successful with them.
Nuclear Bombardment Reactions
Nuclear fusion could be done with two
hydrogen isotopes (tritium & deuterium),
but would still require a temperature of
50 – 100 million kelvin.
Putting the matter in a Plasma state.
Nuclear Bombardment Reactions
Einstein’s Theory of Relativity
The Theory of Relativity shows the amount
of energy released in a Nuclear Reaction:
E=
2
mc
Energy = mass x speed of light2
Dmetri Mendeleev
Mendeleev was a Russian scientist who, in
the 1860’s, began to organize the
elements.
He arranged them into 8 groups with similar
properties.
These he placed into columns.
Dmetri Mendeleev
Mendeleev’s “table” had gaps.
Why?
He predicted these to be elements that were
yet to be discovered.
He further predicted the properties of these
“missing” elements.
The Periodic Table
Mendeleev organized the elements into
rows by increasing atomic mass.
…into columns by similar properties.
His table clearly showed that the properties
of the elements repeat in an orderly
fashion.
The Periodic Law
Due to the repeating periodic pattern of the
elements, Mendeleev called this…
Periodic Law
Classification by Atomic Number
There were some problems with
Mendeleev’s table arranging by atomic
masses…
In 1914, Henry Mosely changed the table to
be arranged by atomic numbers
(The number of protons in the nucleus)
Periodic law is now based on atomic
numbers instead of atomic masses.
Periodic Law
The chemical properties of the elements are
periodic functions of their atomic numbers.
When the elements are arranged according
to their atomic numbers, the properties of
the elements repeat.
Electron Levels
Energy Levels
Neils Bohr discovered atoms had
different energy levels.
Electrons close to the nucleus were less
energetic…
Electrons further away were more energetic.
Electron Levels
The number of energy levels an atom has
depends on the number of electrons it
possesses .
Electron Levels
How do we know how many electrons an
atom has?
The number is protons (atomic number) is
the same as the number of electrons.
Filling Order
1. Energy levels have a limit to the # of
electrons they can hold.
* Two can occupy the lowest
energy level.
*The second can hold 8
*The third can hold 18
*The forth can hold 32
Filling Order
2. The maximum number of electrons in the
outermost energy level of an atom is 8.
This is called the Octet Rule.
Once 8 electrons have entered an energy
level, the next 2 electrons must enter a
higher energy level before any unfilled
lower energy level may be filled.
Electron Configuration
The electron configuration of an atom is the
number of electrons in each energy level.
Sodium Electron Configuration
Filling Order
Electrons in the outermost region of the
atom are called Valence Electrons.
Relationships Among Elements
Families
All the elements in a vertical column on the
table have the same # of valence
electrons.
For example:
Oxygen: 6 valence electrons
Sulfur: 6 valence electrons
Families
Oxygen and sulfur are in the same family or
group.
These families have their own names…
Families
Group 1 (IA)
Alkali metals – 1
valence electron
Families
Group 2 (IIA)
Alkaline-earth Metals –
2 valence electrons
Families
Group IB – VIIIB
Transition Metals – 1 or 2 valence electrons
Families
Group 13 (IIIA)
3 valence electrons
Families
Group 14 (IVA)
Carbon Family – 4 valence electrons
Families
Group 15 (VA)
5 valence electrons
Families
Group 16 (VIA)
Oxygen Family – 6 valence electrons
Families
Group 17 (VIIA)
Halogens – 7 valence electrons
Families
Group 18 (VIIIA)
Noble Gases – 8 valence electrons
Inert: Non-Reactive
Periods
Horizontal Rows
Elements in the rows have nothing in
common, but it does help you know
valence electrons and energy levels!
Periodic Trends
Metals
75% of the elements are classified as
metals.
Periodic Trends
Metalloids
• These elements have both properties of
metals and nonmetals
• They are semiconductors…
that is…
They slightly conduct electricity.
Silicon is the most well known metalloid.
Periodic Trends
Non-Metals
Hydrogen and the remaining elements on
the right side of the table are non-metals.