Docstoc

ACHM 111_Week 2 Atoms and molecu

Document Sample
ACHM 111_Week 2 Atoms and molecu Powered By Docstoc
					General information
                  Dr. Kyriacos Kyriacou



• Biochemistry, BSc, UK, 1977

• Biochemistry, PhD, UK, 1982

   • Spent 15 years in UK

  • At Frederick since 1991

                                          2
                                    Chemistry ACHM 111



• 4 ECTS , lecture and lab

• Lecture once a week

         Group 1: Mondays 6:00-9:30 PM
         Group 2: Tuesdays 6:00-9:30 PM

• Laboratory: Later in the course

                                                     3
                               Chemistry ACHM111

               Course assessment

• Course work 40%:
                   i.     20% Mid Term Exams
                   ii.    10% Laboratory work
                   iii.   10% Quiz



• Final Exam 60%
                   Total: 100%
                                                   4
Chemistry and Engineering




                            5
                                      Advice


• If you are worried about chemistry, don’t get
  behind! Keep up with reading, homework etc
• If I seem to think you know more than you
  really do, let me know
• Get help if you need it (classmates, TA`s, me..)
• Focus on understanding, not just on guessing
  what might be on exams


                                                     6
Atoms and molecules

     ACHM 111
              Particles
• Atoms
• molecules
                         What's an atom?

                 Definition:
A microscopic small particle that could not
be made any smaller and still behave as a
 chemical system. Atoms are the smallest
   particles that can exist and represent
    elements identity. Atoms cannot be
           created or destroyed
                                   Atoms

• Atoms consist of protons, neutrons, electrons
• The atomic structure is shown in the diagram
  below
• Protons have positive charge
• Electrons have negative charge
• Neutrons have no charge
ATOMIC STRUCTURE
ATOMIC STRUCTURE
                           Properties
           Particle    Mass (kg)         Mass (amu)#    Charge*

Electron              9.10939 x 10 -31    0.00055 = 0     -1

Proton                1.67262 x 10 -27    1.00728 = 1     +1

Neutron               1.67493 x 10 -27    1.00866 = 1      0
                     Atoms

•   Sub-atomic particles
•   Electrons
•   Protons
•   neutrons
             ATOMIC PARTICLES:

• Atoms consist of three subatomic particles:
• electrons
  – electrons are negatively charged particles and their
    properties are summarized in the following table
• protons
  – protons are positively charged particles and their
    properties are summarized in the following table
• neutrons
  – neutrons have no charge and their properties are
    summarized in the following table
                 ELECTRONS
•   Small negatively charged particle
•   Orbit, circle, around the nucleus
•   Have no mass.
•   Atoms are neutral.
•   Number of electrons = number of protons
                 PROTONS:

• small, positively charged particles
• reside in the nucleus
• along with the neutron, make up most of the
  mass of the atom
• the number of protons is what defines the
  type of a particular atom.
• Atoms are neutral
• Number of protons = number of electrons
                NEUTRONS:

• small particles with no charge
• reside in the nucleus
• along with the proton, make up most of the
  mass of the atom
• a differing number of neutrons is what defines
  an "isotope" of an atom
    ATOMS--Dalton's Atomic Theory

• All matter (including elements) is composed of
  atoms; each atom is a very small, chemically
  indivisible particle
  – the word 'atom' is from the Greek word "atmos"
    which means "cannot be cut apart"
• elements are different because they are
  composed of different types of atoms
• each type of atom has properties different
  from other atoms
       Atomic theory of matter
• Matter composed of atoms
• Atoms of given element have identical
  properties
• Different elements have different properties
• Atoms combine in whole number ratios
• Not created or destroyed in ordinary chemical
  reactions
     What's a molecule?

              Definition:
The smallest particles of an element or
 compound that can exist and retain the
 chemical properties of that element or
               compound
              Molecules
•Molecular formula gives composition:
number of atoms of each element
present
•Molecular mass= sum of masses of
atoms
EXAMPLES OF MOLECULES
Examples of molecules
                  Atomicity
The atoms of the noble gases, Helium, Neon, Mercury
vapour can all exist on their own. These are said to be
monatomic substances- the atom and the molecule
being the same
On the other hand oxygen, nitrogen, hydrogen,
chlorine are diatomic and hence their formula are: 02,
N2, H2, Cl2. there are a few well-known cases of higher
atomicity, such are ozone O3 and white phosphorus P4.
in this sense the molecule is also the smallest particle
of a compound that can exist in the free state.
Definition: the atomicity of a substance whether an
element or a compound is the number of atoms in one
molecule.
      Representing molecules
• Names: ethanol, ethyl alcohol

•Formulas: C2H8O, C2H5OH, CH3CH2OH

•Structural drawings

•Models
Formula
           Matter - particles
• Matter – Elements, compounds, mixtures
• Elements can be made from atoms or
  molecules
• Compounds can be made only from molecules
• Mixtures can be made from either atoms or
  molecules.
           Atomic and molecular structure
All matter living or dead consists of materials. In
nature their are 116 fundamental materials these are
called elements.
Definition: an element is a substance that cannot be
split up into two or more substances by chemical
means.
Elements may be: a. Solid-iron, carbon
                    b. liquids- mercury, bromine
                    c. gases- oxygen, hydrogen

The elements are all composed of particles smaller
than atoms known as electrons, protons and neutrons
                                              Compounds
Only few elements are found free in nature: e.g. carbon,
nitrogen , oxygen, sulphur, the noble gases, copper and gold.
Most elements are found as compounds. Compounds are
formed by two or more elements combining together millions of
compounds are known and carbon is the element that forms the
most.
Definition: a compound is a substance which contains two or
more elements combined in such a way their properties are
changer
Molecules: atoms of an element may not be able to exist singly:
the atomicity of an element is the number if the atoms in on
molecule
Definition: the molecule is the smallest particle of an element
which can exist in the free state under ordinary conditions.
                 Compounds
• compounds are composed of two or more
  atoms chemically combined in fixed
  proportions
  – for example, water, H2O, always occurs in a ratio of
    2 hydrogens : 1 oxygen—
  – if the ratio were anything else it would not be
    water, H2O2 with a ratio of 2 : 2 is peroxide,
    certainly not water
                     Mixtures
A pure substance is one in which all the molecule alike.
Element and compounds are the only pure substances
that can exist. If two or more kinds of molecules are
present together they form a mixture. Most of the
materials encountered are mixtures: air, earth, sea
water, plants. One of the chemicals most important and
difficulty jobs is to sort out the naturally occurring
mixtures into their pure components in order to
characterize them.
Definition: a mixture contains two or more different
substances either elements or compounds, which are
not chemically joined together
              Mixtures and compounds
Mixtures and compounds both contain more than one
element and so should be separable into their component
elements. This process may be easy or difficult but it is
not the only criterion for deciding whether a given
material is a mixture or a compound.
Example: consider two elements iron and sulphur
Iron – form of fillings
Sulphur- form of yellow powder
Mix them together without heat mixture
Heat mixture in a test tube
This process of water of crystallization in a substance e.g.
copper sulphate -5- water does not make it a mixture
because the composition is fixed.
Pure substances
Element, Atom, Compound, Molecule
 • An element is a substance which contains only one kind of
   atom: lead (Pb), silver (Ag), hydrogen (H2), oxygen (O2).
 • An atom is the smallest particle of an element which exhibits the
   physical and chemical characteristics of that element.

 • A compound is a substance which contains two or more kinds of
   atoms: carbon dioxide (CO2), calcium oxide (CaO), sodium
   hydroxide (NaOH).
 • A molecule is the smallest particle of a substance which exhibits the
   physical and chemical characteristics of that substance.
 •    Monoatomic molecules of elements - Cu, Ag, Na, etc.
 •    Multiatomic molecules of elements - H2, N2, O2, F2, Cl2, Br2, I2, P4,
   S8
 •    Molecules of compounds - Na2O, KOH, CaSO4, HBr, H2CO3
                  Atomic structure
• Rutherford developed the "nuclear" model of the atom
   – based upon his experiment which showed that atoms contain
     regions of highly dense, positive material, called the nucleus
   – the nucleus is very dense, 99.95% (or more) of the mass of the
     atom is in the nucleus which has a diameter of approximately 10
     -15 m-- a matchbox of nucleus material would weigh 2½ billion
     tons! The density is approximately 1013 - 1014 g/cm3.
   – Rutherford discovered this through his famous experiment with
     gold foil in which he shot alpha particles (fairly massive particles
     with a positive charge) through thin gold foil and found that
     many particles were strongly deflected and some bounced back
     at him! This could only happen if the gold foil atoms contained
     massive centers that had a positive charge, as exhibited in the
     figure below.
Atomic structure
         Atoms characteristics
• Atomic number identity of atom. Most
  important.
  – Determined by number of protons
• Atomic mass number
  – Sum of number protons plus number of neutrons
             ATOMIC NUMBER:

•
• the atomic number has the symbol, Z, and is
  shown as a superscript to the element symbol
• the atomic number gives the number of protons
  in the nucleus (and the number of electrons if the
  species is neutral) of a particular atom
• the atomic number defines a specific type of
  atom since each different type of atom
  (representing each element) will have a different
  number of protons in the nucleus
        ATOMIC MASS NUMBER

• the mass number has the symbol, A, and is
  shown as a subscript to the element symbol
• the mass number gives the mass of atom in
  amu, atomic mass number, and is
  approximately equal to the number of protons
  plus the number of neutrons
    Law of constant composition
• Reactions take place between whole numbers of
  atoms at constant proportion
• chemical reactions rearrange the atoms
  – by rearranging the atoms and their ratios of
    chemical combination, the substances change
• chemical reactions cannot create or destroy
  matter, they can only rearrange it, therefore
  all atoms in a chemical reaction product, must
  have occurred within the reactants
DNA
Chemistry 3 “Representations”
•Macroscopic or bulk: observations

•Symbolic: written description

•Microscopic/molecular: visualize atoms and
molecules

•One big trick to chemistry is seeing
connections between those views

				
DOCUMENT INFO