Objectives 1. Distinguish between the early schools of thought on the nature of the atom. 2. Know the effects of politics on the development of the atomic theory 3. Know and understand Dalton’s atomic theory 4. Know the subatomic particles and their characteristics 5. Know and understand the modern model of the atom
Objectives (cont.) 6. Describe the behavior of light and carry out calculations. 7. Define and describe isotopes and calculate the weighted atomic mass of an element. 8. Understand the atomic emission spectra. 9. Write electron configurations.
The Development
Electron First subatomic particle discovered JJ Thomson Method of discovery- cathode ray tube Passed electricity through glass tubes with most of the air removed The ray attracted to the positive charge and deflected by the negative charge In 1897 he realized: Electron is negative Mass 1/1800 of proton
Plum Pudding model JJ Thomson proposed this model Uniformly distributed individual electrons on a positive charge sphere
Ernest Rutherford Rutherford’s Gold Foil Experiment (1910) Tested the plum pudding model Discovered: That most of the mass of atom is in the core, named the nucleus The nucleus is positively charged ( protons ) Most of the volume of the atom is empty space
James Chadwick In 1932, he discovered the neutron They have no charge and the mass equal to that of a proton
The Periodic Table
Development of the Periodic Table In the 1700s, Lavoisier compiled a list of all the known elements of the time In the 1800s, John Newlands proposed an arrangement where elements were ordered by increasing atomic mass Newlands noticed when the elements were arranged by increasing atomic mass, their properties repeated every eighth element
Part 2
Development of the Periodic Table Mendeleev realized there was a connection between atomic mass and elemental properties Mendeleev noticed that as atomic mass increased the properties of elements repeated periodically Mendeleev made predictions about the gaps in the table of the undiscovered elements
Development of the Periodic Table A few problems arose with Mendeleev’s organization by atomic mass Moseley arrange the elements by atomic number This is the periodic table we use today
Periodic Table Columns of elements are called groups Rows of elements are called periods periods
Elements Most symbols are formed from the first letter of the element’s name (and sometimes the second letter or third letter) There are exceptions Examples: First letter is always uppercase and the second is always lowercase
Metals
Metalloids Properties between metals and nonmetals
Groups and Families alkali metal family(but does not include H)
alkaline earth metal family
Transition metals Rare earth metals
Nonmetals
halogens
noble gases (or inert gases) noble gases
Chemical Formulas Formulas show the elements and number of atoms of each in a compound Subscripts show the number of atoms Example:
SymbolChargeLocationRelative mass Electrone-In the space surrounding the nucleus 0 amu ProtonP++1In the nucleus 1 amu Neutronn0In the nucleus 1 amu SUBATOMIC PARTICLES
Reading the Periodic Table
For gold: Z: A: # protons: # electrons: # neutrons: Isotopic symbol: Family:
Isotopes Atoms of the same element that have different masses Many elements have only one stable form, while other elements have different “versions” of their atoms Isotopes of the same element have:
Atomic Mass Weighted average of the atomic masses of the naturally occurring isotopes of an element Example: Calculate the atomic mass of nitrogen. Given: 99.63% of nitrogen is nitrogen-14 and 0.37% of nitrogen is nitrogen-15.
Example: Determine the weighted atomic mass. IsotopeMass of one atom % abundance Silicon amu92.21 Silicon amu4.70 Silicon amu3.08
IsotopeMassAbundance Gold % Gold % Gold %
Review Question Which isotope of Argon is most likely to be in the highest percentage? Ar- 36 Ar- 38 Ar- 40