### density problems.

First recall that the units of density are g/cm3 or g.cm-3.

A student found that 20.0 mL of a liquid weighed 35.987 g. What is its density?

Using a jewelers balance a student found that a coin weighed 2.34 carats in air. By weighing it again submerged in water she found it had a volume of 0.034 mL. What is its density? (1 carat = 200 mg, defined)

### pressure problem.

What is the force in Newtons on the surface of water in a 10.00 x 10.00 cm square container (area = 100.0 cm2) if the pressure is 754 mmHg?

### Units

1 mmHg = 1 Torr, and 760 mmHg = 1.013 x 105 Pa

1 pascal (Pa) = 1 Nm-2 = 1 N/m2 or 1 N = (Pa)(m2)

104 cm2 = 1 m2

## Dalton's atomic theory

### Atoms are now known to consist of three different types of particles: electrons, protons and neutrons

 Particle Charge Relative Mass Mass Electron (e-) -1 1/1840 9.11 x 10-28g Proton (p or H+) +1 ª1 1.67 x 10-24g Neutron (n) 0 ª1 1.67 x 10-24g

• Atomic number (Z) - the number of protons in the nucleus. This number is characteristic of a given element.
• Atomic mass number (A) - the sum of the protons and neutrons in a given atom (p + n).
• Atomic mass - the actual mass of an average atom in a sample. The characteristic atomic masses for Earth are shown on periodic tables.
• Atomic Mass Unit: the atomic mass unit = amu is a unit of mass for atoms. It is defined as 1/12 the mass of one atom of 12C, where the mass of 12C is defined as 12 exactly.