Atomic Structure

Protons = Positive Neutrons = Neutral Electrons = Negtive

4 = Mass Number - equal to the total number of protons and neutrons.2 = atomic number or proton number.

To find the number of : PROTONS - equal to the atomic number. ELECTRONS - equal to the atomic number. NEUTRONS - mass number minus atomic number.

Electrons are located outside the nucleus in rings called 'shells' or 'energy levels'.The inner most energy level takes 2 electrons, the second and third can take up to 8.

All atoms want a full outer shell of electrons. When they react and form bonds with other atoms, they do so in such a way as to obtain a full outer energy level.There are three main types of bond: Covalent - between two non-metal atoms Metalic - between metal atoms Ionic - between a metal and non-metal, the oppositely charged ions are attracted to one another by a strong electrostatic force.

Atoms - found on the periodic table, no overall charge. Ions - made from atoms, either positive or negative charge. Metals - form positive ions. Non-metals - form negative ions.

When two substances react together they make a new substance and it is difficult to separate them. Some atoms react by sharing electrons - we call this ionic bonding. Other atoms react by gaining or losing electrons - we call this covalent bonding. When atoms react in this way they tend to get the electronic structure of a noble gas.

Covalent BondingWhen non-metals react together they share electrons to form molecules. When they react together neither atom can give away electrons, so they get the electronic structure of a noble gas by sharing electrons. The atom in the molecules are then held together because they are sharing pairs of electrons.Sometimes in covalent bonding each atom brings the same number of electrons to the reaction for sharing.Sometimes one element will need several electrons, while the other only needs one more electron for a stable arrangement. In this case, more atoms become become involved in this reaction.There are two types of covalent substance: Simple molecular substances Giant crystal structures.

Simple Molecular SubstancesThey consist of small groups of covalentley-bonded atoms. Between molecules there are weak inter-molecular forces.They are usually liquids or gases because the weak inter-molecular forces between them are easily broken.They have low melting and boiling points.Because they do not contain charged particles (unlike ionic compounds) they do not conduct electricity. 

Ionic bonding When atoms form chemical bonds by transferring electrons, they form ions. Atoms that lose electrons become positively charged ions. Atoms that gain electrons become negatively charged ions. Ions have the electronic structure of a noble gas (Group 0). The elements in Group 1 of the periodic table, the alkali metals, all react with non-metal elements to form ionic compounds in which the metal ion has a single positive charge. The elements in Group 7 of the periodic table, the halogens, all react with the alkali metals to form ionic compounds in which the halide ions have a single negative charge.

Metallic Bonding Metals usually have only a few outer energy-level electrons. When metal atoms bond to each other these outer electrons become delocaslised. The remaining metal ions are arranged in layers surrounded by a 'sea' of delocalised electrons.

Properties of MetalsThe delocalised electrons are free to move and can carry an electrical charge, - metals conduct electricity.The layers of metal can slide over one another due to the 'lubrication' provided by the delocalised electrons, - metals are malleable and ductile.

Giant Crystal/Covalent StructureIn these substances all the atoms are joined to the atoms next to them by covalent bonds.Because these bonds are very strong these structures tend to be extremely strong and hard.   e.g diamond, silicon dioxideIn diamond each carbon atom is covalently bonded to 4 other atoms.In silicon dioxide (SiO2) each silicon atom is covalently bonded to 4 oxygen atoms.A Special Case: Graphite.Carbon has 4 electrons inits outer energy level:In diamond all of these are used to bond to other carbon atomsIn graphite, only 3 are used for forming covalent bonds.The delocalised electrons are free to move, for this reason graphite conducts electricity. it is also a soft substance because the layers of carbon atoms can slide over one another. Each carbon atom is covalently bonded to 3 others.

PolymersPolymers may be natural (e.g. protein or DNA) or artificial (e.g.) poly ethene or polyester). They are all made up of monomers.Their properties depend on their bonding.They are made up of molecules (-a molecule is made up of a group of atoms that are covalently bonded together-) The molecules are large and there are many inter-molecular forces between them.Because of these forces, polymers are usually solid at room temperature. But they are often easily melted because little energy is needed to break the inter-molecular forces. 

Structure And Bonding