Atoms, Molecules, And Ions

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Chapter 2
Atoms, Molecules, and Ions

Summary of the Chapter
• Atomic Structure: protons, electrons and neutrons
• The Periodic Table: how is the periodic table organized, metallic and non metallic elements

• Molecules and Molecular Compounds: chemical formula • Ions and Ionic Compounds: predicting charges, names and formulas
• Binary Molecular Compounds: names and formulas

Atomic Theory of Matter
A little bit of history:
• Democritus (460–370 BC) and other Greek philosophers were the first in postulate that all matter can be divided into indivisible “atomos”.
• Dalton (1803-1807) proposed atomic theory with the following postulates:
1. Elements are composed of atoms.
2. All atoms of an element have identical chemical properties. 3. In chemical reactions atoms are not changed into different types of atoms. Atoms are neither created nor destroyed.
4. Compounds are formed when atoms of elements combine. History of Discovery of Atomic
• J.J. Thomson (1856-1940)-discovery of electron and its charge-to-mass ratio
– Cathode rays
• Robert Millikan (1868-1953) - mass of electron
• Rutherford (1871-1937) - thorough radioactivity, discovery of α (+2 charged), β (-1 charged) and γ (neutral) particles
– Nuclear model of atom, nucleus
– Discovery of protons
• James Chadwick (1891-1972) - neutrons

The Electron

Thomson measured the charge/mass ratio of the electron to be 1.76  108 coulombs/gram

Discovery of the Nucleus

Ernest Rutherford shot  particles at a thin sheet of gold foil and observed the pattern of scatter of the particles. Atomic Structure
• The atom is constituted of three subatomic particles which are _________, _________ and _________.
• ___________ and ___________ are located in the nucleus of the