Home Chemistry CHEMISTRY: A Textbook for Grade 10   Chapter 1: Introduction to Chemistry

E-Lecture - Important Point
  • The science of chemistry deals with the composition, physical properties, and chemical properties of matter.
  • The SI system has seven base units, six of which are used in chemistry.
  • Some measurements are expressed directly in terms of base units as well as multiples or submultiples of a base unit. For example, you might express a length in meters as well as in kilometers or millimeters.
  • A measured quantity must be expressed with the proper number of significant figures to indicate its precision.
  • In reporting calculated quantities special attention must be paid to the concept of significant figures.
  • Calculations can be done by the unit-conversion method.
  • Techniques of estimating answers are also useful in problem solving.
  • The scientific method involves making observations, doing experiments forming hypothesis, gathering data, and formulating laws and theories.
  • A chemical symbol is a shorthand notation for the chemical name of an element.
  • The first letter of a symbol is always capitalized, but the next letter is not.
  • A chemical formula is the symbolic representation of a substance giving the ratios of different kinds of atoms in it.
  • The formula of an element consists of one kind of symbol.
  • The formula of a compound consists of two or more kinds of symbols.
  • Molecules containing only two atoms are called diatomic molecules.
  • Molecules containing more than two atoms are called polyatomic molecules.
  • The combining power of an element or polyatomic ion is called valence number.
  • Binary compounds contain atoms of two different elements only.
  • A prefix is a letter or group of letters added to the beginning of a word.
  • The formulas of compounds can be written if the symbols and valence numbers of the constituent elements or polyatomic ions are known.
  • Qualitatively a symbol represents the identity of the element.
  • Quantitatively a symbol represents the number of atoms of the elements.
  • Qualitatively a formula represents the kind of elements involved in making a compound.
  • A formula stands for one molecule or formula unit of a molecule or a compound.
  • A number in front of a symbol or a formula is called a coefficient.
  • A subscript is written on the bottom right hand side of a symbol.
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