Topic 2 The periodic table and bonding

The periodic table

• Vertical columns are called groups, The group to which an element belongs corresponds to the number of electrons it has in the outer shell.

• The rows are called periods, The properties of elements change as you go along a period

The element in any group all have the same number of electrons on there outer shell that is why they have similar properties

Electron shells

1. Electron alwyas occupy shells (Energy levels)

2. The lowest energy levels are always filled first

3. Only a certain number of electrons are allowed in each shell

4. the order in how many electrons they can contain is 2.8.8

More on the periodic table

The elements can be classified as metals or non metals

Metals

• The elements on the left of the zigzag are classified as metals

• Metals conduct electricity becuase they allow charge to pass through them easily

• Metal oxides are basic this means they will neutralize acids. Metal oxides which dissolve will form solutions with a ph of more than 7

Non - metals

• The elements on the right of the zigzag are all classified as non metals

• non metals are poor conductors of electricity

• non metal oxides are acidic. This means that they will neutralize bases. They dissolve in water to form solution with Ph of less than 7

Group 0

They are the noble gases they are colorless. They are inert wich means they dont react with much at all. The reason for this is that it takes a lot of energy to add or remove electrons from noble gas atom

Ionic bonding

• Ions are charges particles, they can be a single atom or a group of atoms

• Negative ions (anions) are formed when atoms gain electrons wich means they have more electrons that protons

• Positive ions (cations) form when atoms lose electrons which means they have more protons than electrons

• The number of electrons gained or lost is the same charge on the ion.

• Group 1,2,3 elements are metals they lose electrons to form positive ions

• Group 5,6,7 elements are non metals they gain electrons to form a negative ion

Transfer of electron

• When a metal and non metal react together to create an anion and a cation.

• These oppositely charged ions are strongly attracted to one another by electrostatic force of attraction. This attraction is called ionic bonding.

Ionic compounds

Ionic compounds have a lattice structure

• Compounds with ionic bonding always have ionic structures

• The ions are held close together in a closely packed 3D lattice arrangement by the attraction between oppositely charged ions.

• The electrostatic attraction between oppositely changed ions is very strong becuase a lot of energy is needed to overcome the strong attraction, Ionic compounds have a high melting and boiling point

Ionic compounds are not electrical conductors when they are solid. But if you melt them or dissolve them in water they are able to conduct electricity

Covalent Bonding

Sometimes atoms make covalent bonding by sharing pairs of electrons with other atoms.

• Each covalent bond provides an extra shared electron atom

• In covalent bonding there’s a strong electrostatic attraction between the negatively charged shared electrons and the positively charged nuclei of atoms.

Covalent substances

Simple Molecular substance

• The atoms within a molecule are held togther by very strong covalent bonds.

• By contrast the forces of attraction between the molecules are very weak, the result of Theas weak intermolecular forces the melting and boiling point is very low, becuase the molecules are easily separated

Giant covalent structures

• These are similar to giant ionic structures except that there are no charged ions.

• They have a strong covalent bond meaning it is harder to over come the forces of attraction , therefore they have a higher melting and boiling point

Fullerene

• A hollow sphere made up of 60 carbons

• they are made of large covalent molecules

• they are held by intermolecular forces so its soft

• Have no delocalized electrons, cannot conduct electricity.

Electrical conductivity and metals

• When electrons or ions move they can cause the material they’re in to conduct electricity

• The electric current is the flow of the electrons or ions

Ionic compounds only conduct electricity when molten or in a solution. This is becuase in a solid state the protons and electrons are close togther, the electrons can only freely move around when melted of in water because the protons and electrons are further apart.

Metals are held together by metallic bonding, (electrostatic forces of attraction) wich makes them good conductors of electricity and heat.