1.1 Chemistry: An Overview

Science: A Process for Understanding Nature and Its Changes

• Fundamental elements of science:
  1. Making observations (collecting data)
     1. Observations may be qualitative or quantitative.
     2. A qualitative observation does not involve a number.
     3. A quantitative observation (called a measurement) involves both a number and a unit.
  2. Suggesting a possible explanation ( formulating a hypothesis)
     1. A hypothesis is a possible explanation for an observation.
  3. Doing experiments to test the possible explanation (testing the hypothesis)
     1. An experiment is carried out to test a hypothesis.
     2. This involves gathering new information that enables a scientist to decide whether the hypothesis is valid - that is, whether it is supported by the new information learned form the experiment.
     3. Experiments always produce new observations, and this brings the process back to the beginning again.

1.2 The Scientific Method

Scientific Models

• A theory, which is often called a model, is a set of tested hypotheses that gives an overall explanation of some natural phenomenon.
• Generally observed behavior is formulated into a statement called a natural law.
  • The observation that the total mass of materials is not affected by a chemical changed in those materials is called the law of conservation of mass.
• A law summarizes what happens; a theory (model) is an attempt to explain why it happens.

1.3 Units of Measurement

• In 1960, an international agreement set up a system of units called the International System, or the SI system.

• Table 1.1 Fundamental SI Units

  Physical Quantity	Name of Unit	Abbreviation
  Mass	kilogram	kg
  Length	meter	m
  Time	second	s
  Temperature	kelvin	K
  Electric current	ampere	A
  Amount of substance	mole	mol
  Luminous intensity	candela	cd

• Table 1.2 Previses Used in the SI System

  Prefix	Symbol	Exponential Notation
  exa	E	$10^{18}$
  peta	P	$10^{15}$
  tera	T	$10^{12}$
  giga	G	$10^{9}$
  mega	M	$10^{6}$
  kilo	k	$10^{3}$
  hecto	h	$10^{2}$
  deka	da	$10^{1}$
  —	—	$10^0$
  deci	d	$10^{-1}$
  centi	c	$10^{-2}$
  milli	m	$10^{-3}$
  micro	$\mu$	$10^{-6}$
  nano	n	$10^{-9}$
  pico	p	$10^{-12}$
  femto	f	$10^{-15}$
  atto	a	$10^{-18}$

• Table 1.3 Some Examples of Commonly Used Units

  | Length | A dime is 1 mm thick. A quarter is 2.5 cm in diameter. The average height of an adult man is 1.8 m. | | --- | --- | | Mass | A nickel has a mass of about 5 g. A 120-Ib person has a mass of about 55 kg. | | Volume | A 12-oz can of soda has a volume of about 360 mL. |

• Mass is a measure of the resistance of an object to a change in its state of motion.

• The force that gravity exerts on an object is called the object’s weight.

1.4 Uncertainty in Measurement

• A measurement always has some degree of uncertainty.
  • The uncertainty of a measurement depends on the precision of the measuring device.