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?
Dalton's atomic theory
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All matter is composed of ultimately small particles, called atoms.
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Atoms are permanent and indivisible - they can neither be created nor destroyed.
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Elements are characterized by their atoms. All atoms of a given element are identical in all respects. Atoms of different elements have different properties.
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Chemical change consists of a combination, separation, or rearrangement of atoms.
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Chemical compounds are composed of atoms of two or more elements in fixed ratios.
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.
© R A Paselk
Last modified 1 September 2009