Chapter 2: Atoms, Molecules and Ions
Review of Chapter 1:

Chemistry studies matter and its changes.
Matter is formed by substances and its mixtures.
Atoms are the building blocks of matter.
The different ways atoms combine give rise to different substances.
The composition (kind and number of atoms) and structure (arrangement of atoms) of a substance determine its chemical and physical properties.
In general we can observe the chemical and physical changes of matter with our eyes, without assistance of instruments. It is a macroscopic observation.
It is not so simple to check out the structure of matter. We need the aid of very powerful instruments to determine what is going on at the atomic level, in the very small world, called submicroscopic (or particule), because atoms and molecules are too small to be seem even with a microscope.

Section 2.1: The Atomic Theory of Matter
John Dalton between 1803 and 1807 postulated that :
elements are composed of atoms 
atoms of a given element are identical, atoms of different elements behave differently 
chemical changes do not change atoms into other kinds of atoms, atoms are not created or destroyed in a chemical reaction (Law of Conservation of Matter) 
compounds are formed when atoms from different elements combine, the same compound has always the same composition (Law of Constant Composition)
He was an amazing scientist, and these postulates are still valid today.

Section 2.3: The Modern View of Atomic Structure
Q: Which subatomic particles compose the atom?
Q: Why are atoms electrically neutral?
Q: Which particles give rise to most of the mass of atoms?
Q: Which particles define the size of atoms?
Do: Draw a picture of the helim atom, showing all its subatomic features, including where the charges are located.
Q: What unit is most commonly used to express the mass of an atom?
Q: What are the commonly used units to express the size of atoms?
Q: What is the atomic number (Z) of an atom, and why is it important?
Q: How do we calculate the mass number (A) of an atom, and why is it important?
Q: How do we determine if two atoms are the same element?
Isotopes are atoms with same Z, but different A. 
Do: Give the symbols for the three isotopes of the element carbon. 
Q: Which carbon isotope is the most abundant?
Q: How could we turn a 14C nuclide into a 12C nuclide?
Q: What would happen if we removed 1 neutron from a carbon atom?
Q: What would happen if we removed 1 proton from a carbon atom?
Q: What would happen if we removed 1 electron from a carbon atom?

Section 2.4: Atomic Weights (actually it should be called atomic masses)
We will use atomic masses throughout this course (and in all your future chemistry courses), so make sure you completely understand the concept .
Because the mass of one atom is very small (around 10-22g), a new unit to measure atomic mass was defined:
1 a.m.u. = ________________ g ,and therefore, 1g = ________________ a.m.u.
Because atoms of the same element can have different masses (isotopes!), we need to calculate an average mass for atoms of the same element, which is called (wrongly) atomic weight. 
Do: Solve practice exercise 2.4 on page 46 to apply the concept of weighted average to the calculation of atomic weight of silicon.

Section 2.5: The Periodic Table
Q: What determines how the elements are arranged on the periodic table?
Q: What are the three main pieces of information found in all periodic tables?
Do: Learn:
the symbols and names of all the elements (in subgroup A and the transition metals), 
where to find the metals, metalloids, and nonmetals on the periodic table, 
which elements are solid, which are liquid and which are gases at 25ºC and 1atm.

Practice these concepts by solving EQ 3, on WebAssign.