Principles of Chemistry

1
Principles of Chemistry
CHAPTER 4
ELEMENTS, ATOMS AND IONS
2
Elements

• All matter can be broken down chemically into
  about 100 different elements
• presently there are 117 elements
• 92 elements occur naturally on earth
• The elements vary in abundance
• All of the millions of known substances are made
  up of these elements
• Chemists represent elements using chemical symbols

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3
Distribution of Elements
The 9 most abundant elements account for over 98
of the total mass of elements on the earths
crust, oceans, and atmosphere
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4
Elements in the Human Body
The elements found in living matter is very
different than the distribution of elements on
the crust.
This is an abbreviated list
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5
Symbols for Elements

• Elemental symbols - a set of abbreviations
  representing chemical elements
• Element names are derived from
• Greek, Latin or German words (e.g. Gold - aurum
  latin for shining dawn)
• Elements Colors (e.g. Chlorine and Iodine - greek
  words representing their colors)
• Location where it is discovered (e.g. francium,
  germanium, californium and americum)

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Symbols for Elements

• Elemental symbols - The first letter is always
  capitalized and the second is not
• neon - Ne
• gold - Au
• iron - Fe
• sodium - Na
• Notice that iron and Gold are Fe and Au. These
  symbols are based on their original latin or
  greek names ferrum and aurum

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7
Symbols for Elements

• Sometimes just the first letter is used in an
  elements symbol. In this case capitalize the
  first letter

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8
Symbols for Elements

• In other instances the symbol contains the first
  two letters. Always capitalize the first letter,
  and keep the second letter in lower case

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9
Symbols for Elements

• Other times, a symbol is based on its original
  latin or greek term

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Symbols for Elements

• The reason to follow proper nomenclature is
  illustrated in the following examples
• What is the difference between CO and Co
• CO is Carbon and Oxygen (Carbon Monoxide)
• Co is Cobalt
• Name PB and Pb
• PB is phosphorus and boron
• Pb is lead

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11
Law of Definite Composition

• This law states that any compound is always made
  up of elements in the same proportion by mass
• Take 100g water as an example
• It contains 11.1 g of Hydrogen and 88.9 grams of
  oxygen
• The law of definite composition states that it
  doesnt matter where the water comes from, if you
  take the water from Lake Erie, the Swiss Alps or
  the pond in your backyard - it will always
  contain the same composition of Hydrogen and
  Oxygen

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12
Early Observations

• Most natural materials are mixtures of pure
  substances
• Pure substances are either elements or
  combinations of elements called compounds
• The Law of Definite Composition (also known as
  the Law of constant composition) - a given
  compound always contains the same proportions of
  elements by mass

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13
Daltons Atomic Theory

• Each element is made up of tiny, individual
  particles called atoms
• Atoms are indivisible they cannot be created or
  destroyed
• All atoms of each element are identical in every
  respect
• Atoms of one element are different from atoms of
  any other element
• Atoms of one element may combine with atoms of
  other elements, usually in the ratio of small
  whole numbers, to form chemical compounds

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14
Daltons Atomic Theory
Dalton imagined compounds as collections of atoms
Ball and stick
O
H
H
NaCl
O2
H2O
Formula
O
Wire
Na
O
O
Cl
H
H
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15
Formulas of Compounds

• A compound is a distinct substance that is
  composed of the atoms of two or more elements and
  always contains exactly the same relative masses
  of those elements
• Chemical formula - The types of atoms and the
  number of each type in each unit of a given
  compound is expressed by the chemical formula
• H2O - Subscript (2) refers to 2 hydrogens in the
  chemical formula.
• There is no associated with O, meaning that there
  is just 1 oxygen in the chemical formula

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Rules for Writing Chemical Formulas

• In the chemical formula each atom present is
  represented by its atomic symbol (e.g. Br, O, N,
  H, Mn, Au etc)
• The number of each type of atom is indicated by a
  subscript written to the right of the symbol
  (e.g. in H2SO4 there are 2 hydrogens and 4
  oxygens)
• When only one atom of a given type is present,
  the subscript 1 is omitted

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17
Practice Writing Chemical Formulas
C8H18
Octane
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Practice Writing Chemical Formulas
symbol for carbon
symbol for hydrogen
C8H18
C8H18
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Practice Writing Chemical Formulas
symbol for carbon
symbol for hydrogen
C8H18
C8H18
8 atoms carbon
18 atoms hydrogen
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20
Practice Writing Chemical Formulas
Co(NO3)3
Cobalt(III) Nitrate
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Practice Writing Chemical Formulas
symbol for nitrogen
symbol for cobalt
symbol for oxygen
Co(NO3)3
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22
Practice Writing Chemical Formulas
Co(NO3)3
???????????
1 atom cobalt
3 atom oxygen
1 atom nitrogen
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23
Practice Writing Chemical Formulas
the subscript 3 after a parentheses
means multiply the inside of parentheses by
3 (Y)n Y n
Co(NO3)3
Cobalt(III) Nitrate
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24
Practice Writing Chemical Formulas
the subscript 3 after a parentheses
means multiply the inside of parentheses by
3 (Y)n Y n
Co(NO3)3
Cobalt(III) Nitrate
Co(NO3)3 Co(NO3)(NO3)(NO3) 1 Cobalt atom 3
Nitrogen atoms 9 Oxygen atoms
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25
The Structure of the Atom

• J.J Thomson showed in the late 1890s that the
  atoms of any element can be made to emit tiny
  negative particles
• He demonstrated that these particles could be
  repelled by the negative part of an electric
  field
• These negative particles are known as Electrons
• Thomson knew that atoms were not negative or
  positive and so concluded that atoms must contain
  equal numbers of positive and negative particles.

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The Structure of the Atom

• Ernest Rutherford was interested in
  alpha-particles (a-particles)
• a-particles are positively charged and have a
  mass of 7,500 times the mass electron
• Rutherford devised an experiment where an
  a-particle source directed a beam of a-particles
  at a metal sheet
• a thin metal detector was placed around the metal
  sheet

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Rutherfords Experiment
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Rutherfords findings

• Rutherford found that some a-particles were
  deflected at large angles
• Most particles passed through the foil as he
  expected
• The outcome surprised Rutherford because he
  believed if the current model of the atom was
  correct then the a-particles would crash through
  the foil like a cannonball through paper
• He concluded that the current model of the atom
  was incorrect and that the atom had to have a
  center of concentrated positive charge

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Rutherfords findings
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Rutherfords conclusions

• Nuclear atom - an atom with a dense center of
  positive charge (nucleus)
• The nucleus must have a positive charge to
  balance the negative charge of the electrons
• The nucleus must be small and dense
• Proton - Has a positive charge and the same
  magnitude as an electron (size of charge)
• 1e- 1 proton 0 charge
• In later work with Chadwick a neutron was
  demonstrated. Neutrons have no charge

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Modern Concept of Atomic Structure

• nucleus is made up of protons and neutrons and is
  about 10-13 cm in diameter
• electrons move about 10-8 cm in front of the
  nucleus
• On this scale, if the nucleus was a grape the
  electrons would fly 1 mile away

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Modern Concept of Atomic Structure
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Atomic/Mass Numbers

• Mass number is the sum of protons and neutrons
  in an atoms nucleus
• Atomic number is the number of protons in an
  atoms nucleus
• The mass number is written on top of the atomic
  number in this format C
• Carbon has 6 protons and 6 neutrons for a total
  of 12.

12 6
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34
The Periodic Table

• Periodic Table - Basic organization

11
22.989770
Na
Sodium
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The Periodic Table

• Periodic Table - Basic organization

11
22.989770
Atomic Mass
Atomic Number
Na
Symbol
Sodium
element name
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36
Simplistic Calculation

• Atomic Mass Protons Neutrons
• The atomic mass of carbon 12
• The atomic number of carbon 6 the of
  protons
• neutrons Atomic Mass - protons
• neutrons 12 - 6 6
• Why arent the mass numbers whole on the periodic
  table if were dealing with just protons and
  neutrons and negate electrons mass?
• BECAUSE OF ISOTOPES !

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Isotopes

• All atoms of a given element are not identical
• The characteristic that differentiates one
  element from another is the number of protons
• all oxygen atoms contain 8 protons
• Isotopes are atoms with the same number of
  protons but different numbers of neutrons
• O - contains 8 protons and 8 neutrons
• O - contains 8 protons and 7 neutrons

16 8
15 8
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Periodic Organization
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NaCl
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Periodic Organization
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Electronegativity

• Electronegativity is a measure of the ability of
  an atom or molecule to attract electrons.
• The type of bond formed is largely determined by
  the difference in electronegativity between the
  atoms involved.
• Atoms with similar electronegativities will share
  an electron with each other and form a covalent
  bond.
• If the difference is too great, the electron will
  be permanently transferred to one atom and an
  ionic bond will form

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Periodic Table

• The elements are listed on the periodic table in
  order of increasing atomic number
• They are arranged in specific horizontal rows and
  vertical columns
• Dmitri Mendeleev organized the periodic table
  based on chemical families with similar chemical
  properties
• Families of elements with similar chemical
  properties are arranged in vertical groups

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Periodic Table

• Groups - Groups are referred to by the number
  over the column or by their specific names
• alkali metals - group 1
• alkaline earth metals - group 2
• halogens - group 7
• noble gasses - group 8
• transition metals - spans many vertical columns

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Metals, Nonmetals, Metalloids

• Metal properties - Efficient conduction of heat
  and electricity, Malleability, Ductility,
  Lustrous
• Most of the elements are metals
• Nonmetals - relatively small number of elements
  on the upper-right hand corner of the periodic
  table
• Generally lack properties of metals
• Metalloids - Elements that show a mixture of
  metallic and nonmetallic properties

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References

• Molecular graphics images were produced using the
  UCSF Chimera package from the Resource for
  Biocomputing, Visualization, and Informatics at
  the University of California, San Francisco
  (supported by NIH P41 RR-01081).
• Pettersen, E.F., Goddard, T.D., Huang, C.C.,
  Couch, G.S., Greenblatt, D.M., Meng, E.C., and
  Ferrin, T.E. "UCSF Chimera - A Visualization
  System for Exploratory Research and Analysis." J.
  Comput. Chem. 25(13)1605-1612 (2004).
• NYU Library of 3-D Molecular Structures.
  http//www.nyu.edu/pages/mathmol/library/
• Cracolice, Mark. Peters, Edward. Introductory
  Chemistry An Active Learning Approach. Third
  Edition. Thomson Brooks/Cole. ISBN 0-495-01332-3
• Zumdahl, Steven. DeCoste, Donald. Introductory
  Chemistry A foundation. Sixth Edition. Houghton
  Mifflin Company. ISBN 0-618-80327.

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