Atoms: The Building Blocks of Matter

  • All substances are made of tiny particles of matter called atoms which are the building blocks of all matter.
  • Each atom is made of subatomic particles called protons, neutrons and electrons.
  • The protons and neutrons are located at the centre of the atom, which is called the nucleus.
  • The electrons move very fast around the nucleus in orbital paths called shells.
  • The mass of the electron is negligible, hence the mass of an atom is contained within the nucleus where the protons and neutrons are located.

Carbon atom structure, IGCSE & GCSE Chemistry revision notes

The structure of the carbon atom

Chemical Symbols

  • An element is a substance made of atoms that all contain the same number of protons (one type of atom) and cannot be split into anything simpler.
  • So if you had 500g of pure carbon and divided it into 500 x 1g piles, each pile would contain the same substance and would not differ from any other pile.
  • There is a limited number of elements and all elements are found on the Periodic Table eg. hydrogen, carbon, nitrogen.
  • Each element is represented by its own unique symbol as seen on the Periodic Table e.g. N stands for nitrogen and for nitrogen only.
  • Where a symbol contains two letters, the first one is always written in uppercase letters and the other in lowercase e.g. sodium is Na, not NA.
  • The following elements must be written as molecules as they exist in nature as two atoms joined together: H2, N2, O2, F2, Cl2, Br2 and I2.
  • The atomic number and mass number also shown on the Periodic Table.

Periodic Table Symbol for Carbon - AQA, IGCSE & GCSE Chemistry revision notes

The symbol key for carbon as represented on the Periodic Table

  • Elements take part in chemical reactions in which new substances are made in processes that most often involve an energy change.
  • In these reactions atoms combine together in fixed ratios that will give them full outer shells of electrons, often producing compounds.
  • A compound is a pure substance made up of two or more elements chemically combined and which cannot be separated by physical means.
  • The properties of compounds are usually very different from the elements that form them.
  • There is an unlimited number of compounds and the chemical formula is what tells you the ratio of atoms in a compound.
  • For example H2O is a compound containing 2 hydrogen atoms and 1 oxygen atom.
  • The chemical formula can be deduced from the relative number of atoms present.
  • For example a molecule containing 3 atoms of hydrogen and 1 atom of nitrogen is NH3.
  • Diagrams or models can also be used to represent the chemical formula.

Ammonia-Displayed-Formula, IGCSE & GCSE Chemistry revision notes

The ammonia molecule consists of a central nitrogen atom bonded to 3 hydrogen atoms

Word & Symbol Equations

Word Equations

  • These show the reactants and products of a chemical reaction using their full chemical names.
  • The reactants are those substances on the left-hand side of the arrow and can be thought of as the chemical ingredients of the reaction.
  • They react with each other and form new substances.
  • The products are the new substances which are on the right-hand side of the arrow.
  • The arrow (which is spoken as “goes to” or “produces”) implies the conversion of reactants into products.
  • Reaction conditions or the name of a catalyst (a substance added to make a reaction go faster) can be written above the arrow.
  • An example is the reaction of sodium hydroxide (a base) and hydrochloric acid produces sodium chloride (common table salt) and water:

Sodium hydroxide + hydrochloric acid ⟶ sodium chloride + water

Symbol Equations

  • These use the chemical symbols of each reactant and product that take part in chemical equations.
  • For the reaction of sodium hydroxide (a base) and hydrochloric acid:

NaOH + HCl ⟶ NaCl + H2O

  • There has to be the same number of atoms of each element on either side of the equation as no atoms are lost during a chemical reaction.

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Morgan Curtin Chemistry

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.