CMH 101 Luca Preziati Chapter 5: Atomic Theory Dalton’s Atomic Theory 1.Elements are composed of...
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Transcript of CMH 101 Luca Preziati Chapter 5: Atomic Theory Dalton’s Atomic Theory 1.Elements are composed of...
CMH 101 Luca Preziati
Chapter 5: Atomic Theory
Dalton’s Atomic Theory1. Elements are composed of atoms
– tiny, hard, unbreakable, spheres2. All atoms of an element are identical3. Atoms combine in simple, whole-number ratios to
form molecules of compounds4. In chemical reactions, atoms are not broken or
changed into another type. Just rearranged.
Dalton was able to determine the relative masses of the atoms
Dalton based his scale on H = 1 amu we now base it on C-12 = 12 amu exactly
unit = atomic mass unit (amu or dalton)
John Dalton(1766-1844)
Chapter 5: Atomic Theory
Subatomic Particle
Structure Mass Charge
Neutron ≈ 1 amu 0
Proton ≈ 1 amu + 1
Electron ≈ 0 - 1e-
Chapter 5: Atomic Theory
Rutherford’s Experiment 1909
Chapter 5: Atomic Theory
Isotopes: Atoms with the same number of protons but different number of neutrons.
Isotopes have nearly identical chemical properties.
The neutrons contribute mass and stability to the nucleus. If a nucleus has has too few or too many neutrons, it becomes radioactive (unstable).
Isotopes
H31
A = Mass number
Z = Atomic numberSymbol of element
tritium Common name for this isotope
A = Z + number of neutrons
Chapter 5: Atomic Theory
Ions
• Atoms acquire a charge by gaining or losing electrons•not protons!!
• Ion Charge = # protons – # electrons
• Ions with a + charge are called cations•more protons than electrons•form by losing electrons
• Ions with a – charge are called anions•more electrons than protons•form by gaining electrons
Chapter 5: Atomic Theory
Mendelev (1834 – 1907)
In 1869, the Russian chemist Dmitri Mendeleev arranged the 63 known elements in order of increasing atomic weight starting with hydrogen (later the elements were arranged by atomic number).
Arranged the elements into rows (periods) and found lithium, sodium, potassium started new rows; the properties repeated.
The Periodic Table
Chapter 5: Atomic Theory
Chapter 5: Atomic Theory
Properties of metals:
Solid at room temperature (except for mercury)
Shiny
Conduct electricity
Ductile (can be drawn into wires)
Malleable (can be hammered and rolled into sheets)
Form alloys with other metals
Give up electrons in chemical reactions
Metals
Chapter 5: Atomic Theory
Nonmetals
Properties of non-metals:
Poor conductors of electricity (with the exception of graphite)
Poor conductors of heat
Tend to gain electrons in chemical reactions with metals (with the exception of the unreactive noble gases)
Can either be solid, liquid or gas at room temperature.Eleven are gases and one (bromine) is a liquid at room temperature
Chapter 5: Atomic Theory
Metalloids
There are 8 elements that are classified as metalloids with properties intermediate between those of metals and non-metals.
These elements are in a zigzag band between the metals and non-metals in the Periodic Table.
These elements are boron, silicon, germanium, arsenic, antimony, tellurium, polonium, and astatine. The last two are radioactive.
Chapter 5: Atomic Theory