Chemistry Topic 1

Chemistry Topic 1

1. Atoms and their structure

   • At the centre of an atom is a nucleus containing protons and neutrons. Electrons are arranged around the nucleus in energy levels or shells.
   • particle relative charge proton +1 neutron 0 electron -1
   • The total number of electrons in an atom is always the same as the number of protons in the nucleus. This means atoms have no overall electrical charge.

2. Sub Atomic Particles

   • Each atom consists of a nucleus containing protons and neutrons, with electrons arranged around it in energy levels.
   • Mass number and atomic number
     • The mass number of an atom is never smaller than the atomic number. It can be the same, but is usually bigger: The mass number of an atom is the total number of protons and neutrons it contains The atomic number of an atom is the number of protons it contains

3. 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. However, some isotopes are radioactive.

4. Chemical equations

   • Balanced symbol equations show what happens to the different atoms in reactions. For example, copper and oxygen react together to make copper oxide. Take a look at this word equation for the reaction: copper + oxygen → copper oxide Copper and oxygen are the reactants because they are on the left of the arrow. Copper oxide is the product because it is on the right of the arrow.
     • Notice that there are unequal numbers of each type of atom on the left-hand side compared with the right-hand side. To make things equal, you need to adjust the number of units of some of the substances until you get equal numbers of each type of atom on both sides. Here is the balanced symbol equation: 2Cu + O2 → 2CuO
   • Superscript
     • The small number over the element
   • Subscript
     • The small number under an element