Fundamentals of Atomic Structure

1
Fundamentals of Atomic Structure
2
Fundamental Chemical Laws

• Law of Conservation of Mass-mass is neither
  created or destroyed (Lavoisier)
• Law of Definite Proportions-a given compound
  always contains exactly the same proportion of
  elements by mass (Proust)
• Law of Multiple Proportions-when two elements
  from a series of compounds, the ratios of the
  masses of the second element that combine with 1
  gram of the first element can always be reduced
  to small whole numbers (Dalton)
• (See sample exercise 2.1 on page 42)

3
Daltons Atomic Theory

• Each element is made up of tiny particles called
  atoms.
• The atoms of a given element are identical the
  atoms of different elements are different in some
  fundamental way.
• Chemical compounds are formed when atoms of
  different elements combine with each other. A
  given compound always has the same relative
  numbers and types of atoms.
• Chemical reactions involve reorganization of the
  atoms-changes in the way they are bound together.
  The atoms themselves are not changed in a
  chemical reaction.

4
Subatomic Particles

• The electron was discovered by J.J. Thomson
  through his study of the cathode-ray tube.
• His studies also resulted in the determination of
  the charge-to-mass ratio of an electron.
• e/m -1.76 x 108 C/g
• A new atomic model was developed called the plum
  pudding model.
• In 1909, Robert Millikan performed an experiment
  using charged oil drops which allowed him to
  determine the magnitude of the electrons charge
  (1.60 x 10-19 C).
• This led directly to the determination of the
  mass of an electron (9.11 x 10-31 kg).

5
The Nuclear Atom

• Rutherfords Gold Foil experiment resulted in the
  determination that the atom is mostly empty space
  with a small, dense, positively charged center
  (nucleus).
• The electrons move around the nucleus at a
  distance that is large relative to the nuclear
  radius.
• This model of the atom is also referred to as the
  planetary model.

6
Discovery of the Proton and Neutron

• A positively charged particle equal in magnitude
  to the electron was discovered by Goldstein.
  This particle is 1837 times larger in mass than
  the electron (1.67 x 10-27 kg) and is called a
  proton.
• Chadwick, in 1932, discovered the existence of a
  particle having no charge and almost equal in
  mass to the proton. (1.67 x 10-27 kg) This
  particles is called the neutron.
• See page 50 for a comparison of three subatomic
  particles.

7
Representing Atomic Structure

• The atomic number (Z) is equal to the number of
  protons.
• Since atoms are neutral, the number of protons
  equals the number of electrons.
• The mass number (A) is equal to the number of
  protons and neutrons. (This number is
  approximately equal to the mass of the atom).
• The number of neutrons can be determined by
  subtracting the atomic number from the mass
  number.
• Isotopes are atoms of the same element that have
  different masses due to differing numbers of
  neutrons.

8
Ions

• An atom that gains electrons forms a negative ion
  called an anion.
• An atom that loses electrons forms a positive ion
  called a cation.

9
Find the average score for the following sets of
AP Chemistry data

• Buford High School data 4 students scored a 5
• (22 students total) 11 students
  scored a 4
• 4
  students scored a 3
• 3
  student scored a 2
• 0
  students scored a 1
• Global data 15.5 scored a 5
• (122,000 students total) 19.2 scored a 4
• 20.2 scored a 3
• 15.2 scored a 2
• 30.0 scored a 1

10
Atomic Mass Determination

• The atomic masses listed on the periodic table
  represent the average mass of the isotopes
  composing a sample of the element.
• To determine the average atomic mass, the mass of
  the isotope and the percent abundance must be
  known.

11
Solve the following problem

• An element consists of 1.40 of an isotope with
  mass 203.973 amu, 24.10 of an isotope with mass
  205.9745 amu, 22.10 of an isotope with mass
  206.9759 amu, and 52.40 of an isotope with mass
  207.9766 amu. Calculate the average atomic mass
  and identify the element.

12
Atomic Mass

• The most accurate method for determining masses
  of atoms involves the use of a spectrometer.
• The atomic masses listed on the periodic table
  represent the average mass of the isotopes
  composing a sample of the element.
• To determine the average atomic mass, the mass of
  the isotope and the percent abundance must be
  known.

13
Introduction to the Periodic Table

• The periodic table is organized by increasing
  atomic number.
• Horizontal rows are called periods.
• Vertical columns are called groups.
• Elements within the same group have similar
  chemical properties.

14
Organization of the Periodic Table

• Metals are found on the left side of the table
  and share the following properties
• 1) tend to be solids at room temperature
• 2) have luster
• 3) malleable and ductile
• 4) react with acids
• 5) conduct heat and electricity
• 6) lose electrons and form positive ions

15
Organization of the Periodic Table

• Nonmetals are found on the upper right side of
  the table and share the following properties
• 1) tend to be liquids and gases at room
  temperature
• 2) are dull
• 3) are brittle
• 4) are nonconductors
• 5) dont react with acids
• 6) gain electrons and form negative ions.

16
Organization of the Periodic Table

• Metalloids are elements that have properties of
  both metals and nonmetals.
• Metalloids are located along the diagonal line
  dividing the metals from the nonmetals.

17
Organization of the Periodic Table

• Group 1A alkali metals
• Group 2A alkaline earth metals
• Group 7A halogens
• Group 8A noble gases