Chemistry Topic 1

Chemistry Topic 1

1. What Atoms are and their Structure

   • Atoms are the basic units of matter and the defining structure of elements. Atoms are made up of three particles: protons, neutrons and electrons. Protons and neutrons are heavier than electrons and reside in the center of the atom, which is called the nucleus.
     • Proton
       • In center of the atom, making up the nucleus. Protons have a positive charge.
     • Neutron
       • In the center of the atom, making up the nucleus
     • Electron
       • Electrons surround the nucleus and are negatively charged.
   • The mass number of an atom is its total number of protons and neutrons. Isotopes are atoms of an element with different numbers of neutrons. The relative formula mass of a compound is found by adding together the relative atomic masses of all the atoms in the formula of the compound. The relative formula mass of a substance in grams is one mole of that substance.

2. Isotopes

   • Isotopes are atoms of an element with the normal number of protons and electrons, but different numbers of neutrons. Isotopes have the same atomic number, but different mass numbers. The different isotopes of an element have identical chemical properties.

3. Equations, Subscripts and Coefficients

   • A chemical equation is the symbolic representation of a chemical reaction in the form of symbols and formula, wherein the reactant entities are given on the left-hand side and the product entities on the right-hand side.
   • If there is a subscript below the superscript, it indicates the number of protons, only. Sometimes a superscript is used in connection with atomic charge or ionization.
   • The coefficients give the number of molecules (or atoms) involved in the reaction. In the example reaction, two molecules of hydrogen react with one molecule of oxygen and produce two molecules of water.