· The nucleus consists of 2 particles, Protons and Neutrons.
· An electron orbits the nucleus.
· Nucleus has a positive charge.
· Proton number is also the atomic number and uniquely identifies elements in the periodic table.
· No of protons is the atomic number.
· No of neutrons + no of protons = mass.
The arrangement of electrons in atoms
· Electrons are arranges in shells around the nucleus.
· Each shell is an energy level.
· The lower the energy level the close it is to the nucleus.
· To move an electron from a shell close to the nucleus to further away, (vice versa) we need to add energy to the atom, to overcome the attractive force. Therefore electrons in shells further away from the nucleus have more energy.
· Each energy level can only hold a certain amount of electrons.
· The closest energy level can only hold 2 electrons but the rest can hold up to 8.
· Atoms, such as the noble gases, have a full outer energy level therefore they are very stable.
· Periods are across the periodic table (horizontal rows).
· Group are the vertical rows.
· The electrostatic force is the force generated by differences in electric charge between two particles.
· When atoms react they take part in changes which give them a stable arrangement of electrons. They do this by;
· Sharing electrons (covalent bonding),
· Transferring electrons (ionic bonding).
· In ionic bonding the atoms involved lose or gain electrons so they have a noble gas structure.
· If you gain an electron it is a negative ion, if you lose an electron, it is a positive ion
· Ionic compounds are usually formed when metals react with non metals.
· The ions formed are held with enormously strong forces of attraction between the oppositely charged ions. This electrostatic force of attraction, which acts in all directions, is called an Ionic Bond.
· An ion is a charged atom or molecule. It is charged because the number of electrons does not equal the number of protons in the atom.
· The ionic bonds between the charged particles results in an arrangement of ions we call a giant structure.
· The force exerted by an ion on the other ions in the lattice acts equally in all directions. This is why the ions in a giant structure are held together so tightly.
· The giant structure of ionic compounds is very regular. This is because the ions all pack together neatly.
· Covalent bonding occurs when non-metals react with non-metals and they share electrons
· That atoms in the molecules are held together because they are sharing pairs of electrons and this is known as a chemical bond.
· Giant structures have a huge number of atoms held together by a network of covalent bonds.
· Diamonds are a giant covalent structure. Each carbon atom forms four covalent bonds with its neighbours in a rigid giant covalent lattice.
· Metals are another example of giant structures.
· You can think of metals as a lattice of metal ions, arranges in regular layers
· The outer electrons in each atom can easily move from one atom to the next one.
· The outer electrons form a sea of delocalised electrons surrounding positively charged metal ions.
· Strong electrostatic attraction between the negatively charged electrons and the positively charged ions bond the metal ions together.
· The electrons act a bit like glue!
· Looking closely at metals you can see that it is made up of a number of small crystals which are called grains.
· Sometimes, you can see metal crystals on the surface of steel that has been dipped in zinc to prevent it from rusting. This is known as galvanising. Galvanised steel is used to make channels for carrying electric wires.