Atomic Theory

1

• Atomic Theory
• Daltons Atomic Theory
• Each element is composed of extremely small
  particles called atoms.
• All atoms of a given element are the same, that
  is, they have the same properties such as mass
• All atoms of an element are not changed into
  different types of atoms during chemical
  change atoms are indestructible and thus are
  neither created nor destroyed during chemical
  change
• Compounds are formed when atoms of more than one
  element combine a given compound always has
  the same atoms in a fixed ratio.
• Daltons theory explains some known laws
• Law of Constant composition
• Law of Conservation of Mass
• Daltons theory predicts new laws
• Law of Multiple proportions

2

• Discovery of Atomic Structure
• Cathode Rays and Electrons
• Cathode rays can be bent by magnetic and electric
  fields in a way suggesting they consist of
  negatively charged particles now called electrons
• J. J. Thomson measured the charge-to-mass ratio
  of the electrons.
• 1.76 x 108
• Robert Millikan measured the charge of an
  electron using the oil drop experiment
• 1.60 x 10-19 C
• Combining these results
• mass of the electron 9.10 x 10-28 g
• Radioactivity
• a particles are He atoms without electrons
• b particles are high speed electrons
• g rays are beams of electromagnetic radiation,
  like x-rays

3

• Discovery of Atomic Structure
• The Nuclear Atom
• Rutherford bombarded gold foil with a particles
• He found that the positive a particles were
  scattered
• Mathematical analysis of the scattering showed
  that most of the mass and all the charge in
  gold atoms is in a small volume called the
  nucleus.
• The electrons in the atom must surround the
  nucleus occupying most of the volume of atoms.
• Subatomic Particles
• Particle Charge Mass (amu)
• Proton 1 1.0073
• Neutron 0 1.0087
• Electron -1 0.0005486
• To simplify mass values, the amu - atomic mass
  unit - is 1.66054 x 10-24g
• To simplify charge values, one electronic charge
  unit - 1.601 x 10-19C is 1

4
Modern View of the Atom Some Sizes
Atoms, Nuclei and Elements All atoms of a given
element have the same number of protons in their
nuclei. Atoms of elements are electrically
neutral, thus the number of electrons must equal
the number of protons in an atom of an
element. Isotopes are atoms of an element that
have a different number of neutrons in their
nuclei.
5
Modern View of the Atom Chemical Symbols for
Isotopes Atomic number of protons
in the nucleus Atomic mass number of protons
of neutrons in nucleus neutrons atomic
mass - atomic Other Examples
6
Periodic Table Periodic Law When the elements
are arranged in order of their atomic numbers,
there is a periodic, or cyclic, repetition in
their chemical and physical properties. Periods
are the rows of elements. They are numbered 1,
2, 3, Groups or Families of elements are
vertical columns. They are labeled with Roman or
Arabic numerals and letters Some groups have
common names IA or 1A - alkali metals IIA or
2A - alkaline earth metals VIA or 6A -
chalcogens VIIA or 7A - halogens VIII or 8A -
noble gases A elements - representative or main
group elements B elements - transition metals
7

• Periodic Table
• Metals are along the left and middle of the
  periodic table
• Good electrical and thermal conductors
• Metallic luster
• Malleable and ductile
• Except for Hg, all are solids at room temperature
• Non-metals are in the upper right of the periodic
  table
• Non-conductors of electricity and heat
• Sometimes colored
• Gases, liquid and low melting solids
• Metalloids are on a diagonal separating the
  metals from the non-metals
• Intermediate properties - semiconductors,
  insulators

8

• Molecules and Molecular Compounds
• A molecule is an assembly of two or more atoms
  tightly bound together.
• When the atoms of 2 or more elements are in a
  molecule, this is the smallest particle of such
  a compound.
• Some elements exist as molecules
• O2 oxygen sometimes called dioxygen,
• O3 ozone
• H2 hydrogen sometimes called dihydrogen
• N2 nitrogen sometimes called dinitrogen
• Halogens F2, Cl2, Br2 I2
• S8 sulfur, P4 phosphorus,
• Many compounds are molecular
• HCl, H2O, H2O2, CH4, CO, CO2, C2H4,
• Molecules with two atoms are diatomic

9

• Chemical Formulas
• A chemical formula is representation of a
  molecule of a molecular compound
• Molecular Formulas give the actual number of
  atoms of each element in a molecule
• O2, CO2, CO, H2O, H2O2, C6H6
• Empirical Formulas give the smallest whole number
  ratio of the atoms of each element in a molecule
• For C6H6, its empirical formula is CH
• For H2O2, its empirical formula is HO
• Different compounds may have the same empirical
  formula
• 
  (structural formulas)
• Molecular Formula CH2O C2H4O2
• Empirical Formula CH2O CH2O

10
Representations of Molecules structural
perspective ball-and-stick
space filling formula drawing
11

• Ions and Ionic Compounds
• Ions are atoms or molecules that have gained or
  lost electrons to become charged species.
• Atoms of Metal Elements lose electrons to become
  positively charged ions. Positive ions are
  called cations.
• Atoms of Non-metal Elements gain electrons to
  become negatively charged ions. Negative ions
  are called anions.

12

• Ions and Ionic Compounds
• Polyatomic ions are molecular species that have
  gained or lost electrons
• NO3-, SO42-, PO43- (nitrate ion, sulfate ion,
  phosphate ion)
• NH4, H3O (ammonium ion, hydronium ion)
• Predicting Ionic Charges
• Metal Representative Elements
• Group 1A elements lose 1e, and thus have the same
  of electrons as the previous Noble Gas.
• Na has 11 electrons Na has 10 electrons Ne has
  10 electrons
• Group 2A elements lose 2es and thus have the
  same of electrons as the previous Noble Gas.
• Ca has 20 electrons Ca2 has 18 electrons Ar
  has 18 electrons

13

• Predicting Ionic Charges
• Non-metal Representative Elements
• Non-metal representative elements gain enough
  electrons to have the same number of electrons
  as the next Noble Gas element.
• F has 9 electrons F- has 10 electrons Ne has 10
  electrons
• O has 8 electrons O2- has 10 electrons Ne has
  10 electrons
• N has 7 electrons N3- has 10 electrons Ne has
  10 electrons
• Ionic Compounds
• Ionic compounds usually consist of metal and
  non-metal elements
• Formation of ionic compounds can be considered an
  electron exchange process
• The metal gives up electrons and the non-metal
  gains electrons
• Na Na e-
• Cl e- Cl-
• Na Cl NaCl

14

• Ionic Compounds
• Writing Formulas for Ionic Compounds
• Empirical Formulas are generally written
• From the ionic charges the formulas can be
  readily written
• The charge on the positive ion (cation) becomes
  the subscript after the negative ion (anion)
• The charge on the negative ion (anion) becomes
  the subscript after the positive ion (cation)
• Na2S

15

• Naming Inorganic Compounds
• Inorganic compounds generally do not contain
  carbon
• Naming Cations
• Cations formed from metal atoms are given the
  name of the element
• Na sodium ion Ca2 calcium ion Al3 aluminum
  ion
• Some metals - particularly transition metals -
  can have more than one charge
• Fe2 iron(II) ion Fe3 iron(III) ion
• or
• Fe2 ferrous ion Fe3 ferric ion
• Cu copper(I) ion Cu2 copper(II) ion
• or
• Cu cuprous ion Cu2 cupric ion
• Cations from non-metal elements have names that
  end in -ium
• NH4 ammonium ion H3O hydronium ion
• Learn the Formulas - including charge - and names
  of the ions in Table 2-4, page 59

16

• Naming Inorganic Compounds
• Naming Anions
• Monatomic anions have names formed by dropping
  the ending of the elements name and adding
  -ide
• H- hydride S2- sulfide P3- phosphide
• Some polyatomic anions have names that end in
  -ide
• OH- hydroxide CN- cyanide O22- peroxide
• Oxyanions - polyatomic anions having oxygen -
  have names ending in -ate or -ite
• NO3- nitrate NO2- nitrite
• SO42- sulfate SO32- sulfite
• Oxyanions of the halogens have prefixes in their
  names
• ClO4- perchlorate ClO3- chlorate ClO2-
  chlorite ClO- hypochlorite
• Anions formed by adding H to the oxyanion add a
  prefix word hydrogen or dihydrogen or bi-
• CO32- carbonate HCO3- hydrogen carbonate or
  bicarbonate
• PO43- phosphate H2PO4- dihydrogen phosphate
• Learn the Formulas - including charge - and names
  of the ions in Table 2-5, page 60

17

• Naming Inorganic Compounds
• Name an ionic compound by giving the name of the
  cation followed by the anion.
• LiCl lithium chloride
• Sr(NO3)2 strontium nitrate
• Cu(ClO4)2 copper(II) perchlorate or cupric
  perchlorate
• Note the formula for Cu(ClO4)2 is not written
  CuCl2O8
• Names and Formulas of Acids
• Acids formed from anions whose name ends in -ate
• The acid name ends in -ic
• Acids formed from anions whose name ends in -ite
• The acid name ends in -ous
• NO3- nitrate HNO3 nitric acid
• NO2- nitrite HNO2 nitrous acid

18

• Names and Formulas of Binary Molecular Compounds
• Molecular compounds are formed by the non-metal
  representative elements
• Rules for naming binary compounds
• The name of the element farthest to the left in
  the periodic table is usually written first.
• If both elements are in the same group of the
  periodic table, the lower one is usually
  written first.
• The name of the second element is given an -ide
  suffix.
• Greek prefixes indicate the number of each
  element in the molecule.
• mono is not used with the first element
• when the prefix ends in a or o and the name of
  the anion begins with a vowel, the a or o is
  often dropped
• N2O dinitrogen monoxide NF3 nitrogen
  trifluoride
• NO nitrogen monoxide H2O water - a common
  name
• NO2 nitrogen dioxide NH3 ammonia - a common
  name
• N2O5 dinitrogen pentoxide HCl hydrogen
  chloride
• H2S(aq) hydrosulfuric acid HCl(aq) hydrochloric
  acid