Ionic and covalent bonding
When two elements react together they make a new substance called a compound. It is difficult to seperate the elements after the reaction. Some atoms react by sharing electrons, we call this covalent bonding. Other atoms react by losing or gaining electrons, we call this ionic bonding. when atoms react in this way they get electronic structure of a noble gas.
Ions are particles that have different number or protons and electrons. Ions are electrically charged. Ions can be formed when a metal reacts with a non metal. Metal atoms loose electrons to form posotive ions. Non metals gain electrons from posotive ions. Most ionic compounds are solid a room temperature so they have high melting and boiling points because strong forces of attraction between oppositley charged ions (ionic bonding). Alot of energy is used to over com the strong ionic bonds. They conduct electricity when molten or dissolved but not when solid because ions are free to move and carry electical charge. And are usually soluable in water because water has a posotive and negative end so ions are attracted to water and dissolve.
Properties of covalent substances
Covalent substances have the following properties:
Low melting/boiling point
Insoluble in water
Giant covalent structures
Giant covalent structures contain many atoms joined by covalent bonds. They have high melting points abd boiling points. Diamond is a very hard substance because the carbon atoms in it are held strongly to each other. However, graphite is soft because there are layers of atoms which can slide over eachother. they can do this because there are no covalent bonds between its layers.
In matliclattice there is a very reglar arangment of metal ions. These ions are held together by free moving electrons. This is why all metals can conduct electricity and heat.the more electrons on the outer shell , the better the metal is at conducting. Metalic bonding is posotive ions surrounded by a sea of delocalised electrons. There is strong attraction between ions and delocolised electrons. It has high melting points and is always solid at room tempeature. It conducts electricity and heat. Its malleable. It has a rehular crystal arrangment and an example of metallic bonding in sodium.
Polymers and thier properties
Polymers are made of monomer units.
Monemers undergo a polymerisation reaction and more polymers.
A polymer is a sbstance made from large molecules made up of many repeating units (monomers)
Thermosofening & Thermosetting
Low melting and boiling point / Melts easily
Polymer chains are easy to separate
Forces broken when heated
When polymer cools forces pull the molecules back together
High melting and boiling point / Dosnt melt very easily
Chains fixed together by strong covelant bonds
Bonds stop the chains from seprating
when heated strongly the polymer will burn / char
Nano science is the study of small particles. One nano metre = 10`9 m. Scientist have discovered that at this scale material bahaves differently. This has given rise to many university application but some are worried that there are hazards with particals this small.
Giant ionic structure
Giant ionic structures have a regular 3D structure arrngment of posotive and negative ions. There is strong electrolosis attraction between posotive and negative ions.They have high melting points and are always solid at room temperature and conduct electricity when molten and in solution. they has a regualr crystal arrangment and an example of an giant ionic structure is sodium chloride.
Simple covalent structure
Simple covalent structures are isolated molecules with weak forces between molecules and they have strong bonds between atoms, electrons are shared. They have low melting points, gases and liquids at room temperture and do not conduct electricity. An example of a simple covalent structure is iodine.
Giant covalent structure
Giant covalent structure
Giant covalent structure has a repeating 3D structure with strong bonds between atoms and electrons are shared. They have high melting points almost all are solids at room temperature. Most dont conduct electricity ( excapt graphite ). An exampke of a giant covalent structure is Diamond.