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.
The structure of the carbon atom
- 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.
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.
The ammonia molecule consists of a central nitrogen atom bonded to 3 hydrogen atoms
Word & Symbol 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
- 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’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.