Regents Chemistry

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Regents Chemistry

• Lecture Notes for Topic I
• The Atom

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Elements

• 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
• Example processing of ores to produce metals for
  ornaments and tools

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Elements and Changes early exp.

• Greeks were the first to try to explain why
  chemical changes occur.
• By 400 B.C., they had proposed that all matter
  was composed of four fundamental substances
  fire, earth, water and air
• The next 2000 yearschemical history was
  characterized by alchemy

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Elements early pioneers

• 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

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Elements How many

• 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 Earths crust
• See pg. 87 tables 4.1 and 4.2

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Elements

• 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)

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Elements - symbols

• 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

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Your Assignment

• Read trace elements on pg. 88 and answer the
  following questions in complete sentences
• 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?

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Regent Chemistry

• Evolution of atomic structure

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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
• Daltons Postulates (proposed 1808)
• 1. All elements are composed of indivisible atoms
• 2. All atoms of a given element are identical

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Early Atomic Theory of Matter

• Daltons 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!

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What Daltons Law explains...

• Law of constant composition
• relatives numbers/kinds of atom are constant
• Law of conservation of mass
• total mass before total mass after
• Law of multiple proportions (video)
• For example...

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Same elements and mass before and after reaction
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In the late 1890s

• 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 -

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• 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
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Shortly after...William Thomson aka Lord Kelvin
Concluded atom is a large positive sphere with
electrons floating around like raisons in pudding
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Ernest Rutherford..the famous exp.

• Disproved Thomsons Plum Pudding Model
• How??
• Alpha and Beta particle scattering experiment
  (video)
• The famous gold foil experiment (video)
• Coming up next..modern atomic structure

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Your Assignment

• 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

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Regents Chemistry

• Modern Atomic Theory

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Modern Atomic Theory
The nucleus contains A positive charge..
Nucleus
Electrons surround the nucleus in a cloud
electrons
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Modern Atomic Theory

• Modern atomic theory is based on two models
• The Bohr Model (planetary model)
• The Wave Mechanical Model

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The Bohr Model

• 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!
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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 outwhat 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

• 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
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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

• Classwork
• Read the attached article regarding protons,
  neutrons and electrons. Answer the questions on
  the handout using this information.

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Regents Chemistry

• The Structure of the Atom

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The Nucleus

• A dense centered nucleus contains protons and
  neutronsProtons 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

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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

• 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

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Isotopes cont

• An Isotope is an atom that looses or gains
  neutrons. It is thus lighter or heavier than the
  base atom of the element.

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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 thiseasy!

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Atomic Weights and Isotopes
Multiply the exact weight x abundance for Each
isotope and then add them up!
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Regents Chemistry

• Types of Matter

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What is Matter?

• Matter is the stuff of which the universe is
  composed
• Anything that has mass and occupies space is
  considered matter!

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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

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Mixtures

• For Example

Elements, which are pure substances
AIR
Mixture of oxygen nitrogen, carbon dioxide Argon,
water, others
Compounds, which are pure substances
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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.
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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).
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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...
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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
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Classification of Mixtures

• Homogeneous Mixtures are the same throughout (a
  single phase). ex table salt and water, air,
  brass
• 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
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Examples of Heterogeneous Mixtures

• Sand on a beach
• Cereal
• sand in water
• sugar in lemonade
• 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

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Examples of Homogeneous Mixtures, also called
Solutions

• Air
• Table salt in water
• Solution of Na2SO4
• You cannot see the different substances
• in the mixture (solution) - can be separated
  by chemical or physical means

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Means of Separation

• 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
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(No Transcript)
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Identify each of the following..