Transcript Regents Chemistry

Regents Chemistry
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Lecture Notes for Topic I
The Atom
Elements
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Elements are an extremely important part
of our daily lives
Each element is different and has
different properties and behaviors
Since ancient times, humans have used
chemical changes to their advantage
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Example: processing of ores to produce
metals for ornaments and tools
Elements and Changes –
early exp.
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Greeks were the first to try to explain
why chemical changes occur.
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By 400 B.C., they had proposed that all
matter was composed of four fundamental
substances: fire, earth, water and air
The next 2000 years…chemical history
was characterized by alchemy
Elements – early pioneers
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Robert Boyle (1627 – 1691) – the first
scientist to recognize the importance of
careful measurements.
Defined the term element in terms of
experimentation;
a substance was an element unless it
could be broken down into two or more
simpler substances
Elements – How many
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Presently there are 110 different
elements, of which 88 occur naturally
(the rest have been made in laboratories)
The elements vary tremendously in
abundance
For example, only 9 elements account for
most of the compounds found in the
Earth’s crust
See pg. 87 tables 4.1 and 4.2
Elements
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The term element can used in different
ways
For example, element can mean a single
atom of an element (microscopic view)
Element can also mean a sample large
enough to mass on a balance; this
sample contains many atoms
(macroscopic view)
Elements - symbols
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The names of chemical elements have
many sources; often from Greek, Latin or
German languages
Example; the elemental name bromine
comes from a Greek word meaning
“stench”
We use abbreviations (symbols) in place
of the words
Your Assignment…
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Read trace elements on pg. 88 and
answer the following questions in
complete sentences:
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Name and describe (4) trace elements and their
impacts on our bodies
What is Lithium used for? How does it affect
our bodies?
What did William Walsh discover? How?
Are aluminum and fluoride good for us?
Why or why not?
Regent Chemistry
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Evolution of atomic structure
Early Atomic Theory of Matter
Pre-Dalton – the atom is mostly empty space
and void : The Greeks! Said matter was made
up of particles from four elemental substances :
Earth, water, air and fire
Dalton’s Postulates (proposed 1808)
1. All elements are composed of indivisible atoms
2. All atoms of a given element are identical
Early Atomic
Theory of Matter
Dalton’s Postulates
3. Atoms of different atoms are different; that is,
they have different masses
4. Compounds are formed by the combination of
atoms of different elements. Compounds are
formed in definite proportions!
What Dalton’s Law
explains...
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Law of constant composition
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Law of conservation of mass
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relatives numbers/kinds of atom are
constant
total mass before = total mass after
Law of multiple proportions (video)
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For example...
Same elements and mass before and after reaction
In the late 1890’s
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J.J. Thomson – cathode ray tube with
magnetic fields
Observed nature of rays is the same
regardless of identity of cathode material
1897 – concluded that cathode rays are
not rays but are particles with mass
Generally accepted as the discovery of
the electron -
• High voltage produces radiation within the tube know as
cathode rays
• Movement in tube can be seen as cathode rays
cause certain materials to fluoresce
• Can be deflected by magnetic fields
J.J
Shortly after...William Thomson
aka Lord Kelvin
Concluded atom is a large positive sphere with
electrons floating around like raisons in pudding
Ernest Rutherford..the
famous exp.
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Disproved Thomson’s Plum Pudding Model
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How??
Alpha and Beta particle scattering
experiment (video)
 The famous gold foil experiment (video)
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Coming up next..modern atomic
structure
Your Assignment…
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Write an essay using the information
from this lecture and pg 90-96 in
your textbook. Your essay should
be approximately 500 words in
length and compare/contrast the
contributions of JJ Thomson, Lord
Kelvin and Ernest Rutherford
Regents Chemistry
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Modern Atomic Theory
Modern Atomic Theory
The nucleus contains
A positive charge..
Nucleus
Electrons surround the
nucleus in a “cloud”
electrons
Modern Atomic Theory
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Modern atomic theory is based on
two models
The Bohr Model (planetary model)
 The Wave Mechanical Model
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The Bohr Model
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Neils Bohr proposed a model of the
atom with a dense, positive charge
in the center and electrons
surrounding the nucleus in specific
orbits..
Ask me!
Location of electrons –
energy levels
Electrons are in specific levels
according to the amount of energy
they contain
 There are maximum numbers of
electrons for each level
 Electrons can jump from one level to
another by absorbing or emitting
photons of energy..
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Location of electrons
We can identify an elements
electrons distribution by looking at
the periodic table
 These number describe how many
electrons are in each level
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Jumping of Electrons
Check this out…what happens when
we excite the electrons of specific
metals?
 Why do we see a color?
 Why do different metals show
different colors?
 Can we get any other info from this
demo?
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Jumping levels
Electrons in a non excited state are
said to be in the ground state
 We just observed how to excite
these electrons..
 But how does this change an
elements electrons distribution
 Check out your PT…
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Spectral Lines
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When electrons are emitted or
absorbed from specific elements, we
see the result in two ways..
Emission Spectra
 Absorption Spectra
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Emission and Absorption
Spectra
The Wave – Mechanical
Model
Most current model of electron
behavior
 Proposes electrons are in orbitals,
which are regions of high probability
of finding an electrons
 Also called the electron cloud model
 Why this model?…because of wave
behavior of electrons
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Modern Atomic Theory
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Classwork…
Read the attached article regarding
protons, neutrons and electrons. Answer
the questions on the handout using this
information.
Regents Chemistry
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The Structure of the Atom
The Nucleus
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A dense centered nucleus contains
protons and neutrons
Protons are (+)
Neutrons have no charge
These have a mass of 1 amu and make
up most of the mass of an atom
This mass is called an elements atomic
mass
Subatomic Particles
We measure the mass of protons
and neutrons in atomic mass units
(amu)
 The atomic mass unit is based on
1/12 the mass of the C – 12 isotope
 The protons define an element
 This is called an elements Atomic
Number
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Isotopes
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WE CAN NEVER CHANGE AN ELEMENTS
ATOMIC NUMBER (# p)
We does vary is an elements number of
neutrons
Atoms of the same element that have
different numbers of neutrons are called
Isotopes
C – 14 and C – 12 are isotopes
Isotopes cont…
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An Isotope is an atom that looses or
gains neutrons. It is thus lighter or
heavier than the base atom of the
element.
Average Atomic Mass
The atomic mass listed on the
Periodic table is actually the average
of all known atomic masses for that
element
 How do we do this…easy!
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Atomic Weights and
Isotopes
Multiply the exact weight x % abundance for
Each isotope and then add them up!
Regents Chemistry
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Types of Matter
What is Matter?
• Matter is the “stuff” of which the
universe is composed
• Anything that has mass and
occupies space is considered
matter!
Mixtures and Pure Substances
• A mixture is something that has variable
composition.
– Example: soil, cereal, air
• A pure substance will always have the same
composition. Pure substances are elements or
compounds.
– Example: pure water, table salt, carbon
Mixtures
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For Example:
AIR
Mixture of oxygen
nitrogen, carbon
dioxide
Argon, water, others
Elements, which are
pure substances
Compounds,
which are pure
substances
Elements and Compounds
Pure substances have an invariable composition and
are composed of either elements or compounds.
Elements
"Substances which cannot be decomposed into
simpler substances by chemical means".
Compounds
Can be decomposed into two or more elements.
Elements
Elements are the basic substances out of which all
matter is composed.
Everything in the world is made up from only 110
different elements. 90% of the human body is
composed of only three elements: Oxygen,
Carbon and Hydrogen
Elements are known by common names as well as by
their abbreviations (symbols).
Compounds
Compounds are substances of two or more elements
united chemically in definite proportions by mass.
The observation that the elemental composition of a
pure compound is always the same is known as the
law of constant composition (or the law of definite
proportions).
For Example...
Good Old H2O
For example, pure water is
composed of the elements hydrogen
(H) and oxygen (O) at the defined
ratio of 11 % hydrogen and 89 %
oxygen by mass.
Worksheet
Classification of Mixtures
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Homogeneous Mixtures – are the
same throughout (a single phase).
ex: table salt and water, air, brass
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Heterogeneous Mixtures – contain
regions that have different properties
from those of other regions (more
than 1 phase). ex: sand in water, cereal
Phase - area of uniform composition
Examples of
Heterogeneous Mixtures
Sand on a beach
 Cereal
 sand in water
 sugar in lemonade
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Most of the time you can see the
different substances, hence the
mixtures are said to be not well
mixed and can be separated
physically
Examples of Homogeneous
Mixtures, also called Solutions
Air
 Table salt in water
 Solution of Na2SO4
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You cannot see the different
substances
in the mixture (solution) - can be
separated by chemical or physical
means
Means of Separation
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Use a magnet - physical
 Ex: Iron and sand mixture
• Filtration - physical
Ex: sand and water mixture
• Distillation - physical
Ex: salt and water mixture
see distillation apparatus
• Electrolysis - chemical
Ex: water - see video
- worksheet
Identify each of the following..