原子和元素

Scientific Laws In science, a law is defined as a concise, verbal or mathematical, statement that summarizes a vast number of experimental observations. …

Chemistry is an empirical science. Scientists often pose questions to understand the chemistry in everyday life and seek answers to these questions. To …

Chemistry is the study of matter and the changes it undergoes. Matter is anything that has mass and occupies space. Matter is all around us; the air, …

Matter: Pure Substances and Mixtures According to its composition, the matter can be classified into two broad categories — pure substances and …

The characteristics that enable us to distinguish one substance from another are called properties. Physical Properties of Matter A physical property is …

The universe is composed of matter in different forms, and all forms of matter contain energy.  The different forms of energy on Earth originate from …

Every measurement provides three kinds of information: the size or magnitude of the measurement (a number), a standard of comparison for the measurement …

The International System of Units or SI system, by international agreement, has fixed measurement units for seven fundamental properties: length, mass, …

Scientists typically make repeated measurements of a quantity to ensure the quality of their findings and to evaluate both the precision and the accuracy …

Counting is the type of measurement that is free from uncertainty, provided the number of objects being counted does not change during the process. Such …

All the digits in a measurement, including the uncertain last digit, are called significant figures or significant digits. Note that zero may be a …

Dimensional analysis, also known as the factor label method, is a versatile approach for mathematical operations. The main principle behind this approach …