Chem Notes Igcse

Giant Covalent Structures There are 2 examples of Giant covalent structures: Diamond Graphite They are both  allotropes  of carbon, meaning they are  both different  types of the physical  form of Carbon. Diamond Structure: Giant covalent  lattice  of carbon atoms. Each Carbon atom is bonded to 4 others which tetrahedrally surround the atom. They have a  high melting point  as a large amount of heat energy is needed to break their bonds. They are  unable  to conduct electricity as they have no free mobile  electrons to carry the current.Diamond is very  hard  as there are many bonds within the substance. It is the hardest natural substance and is often used in drilling. Graphite Structure: Arranged in  layers  of atoms. Each carbon atom is joined to 3 others, leaving one outer shell electron on each carbon is free to move and able to cary the current. Therefore, they are able to conduct electricity. Graphite also has a high melting point for the same reasons as diamond. However, it is not hard like diamond but in fact very soft. There are weak forces between  the  layers of atoms.They  are able to slide over each other and therefore able to act as a lubricant. Covalent Bonding Definition:  When an atom shares one or more pairs of electrons between atoms to obtain the electronic configuration of a noble gas. Covalent bonds appear in  non-metals  and create  molecules. They can even appear in atoms of the same element,  H2. Molecule:  Two or more atoms  chemically  bonded together. The covalently bonded atoms are held together by  strong attraction  between the  bonding pair of electrons  and the  nuclei  of the atoms.Covalent bonds can be classified into  two  groups:  simple molecular  structures   giant covalent  structures Simple molecular Structures: They have low melting/boiling points due  to the fact that  there  are  weak  intermolecular forces of attraction. Although, they do have strong covalent bonds. Therefore, they need less heat energy to overcome and break the weak bonds. Some substances  sumblime  under heating. i. e. They turn directly into a gas from a solid. Giant molecular Structures:  See post on giant Molecular structures , Ionic BondingDefinition:  The transfer of one or more electrons between 1 atom to another Why? To obtain the electronic configuration of a noble gas. This  is because noble gases are inert/very unreactive. If an atom  loses  an electron then the atom will form a  positive  ion. This is because there are now more protons than electrons in the atom. If an atom  gains  an electron, the atom forms a  negative  ion as there are now more electrons than protons in the atom. The  charge  of an ion is related to where the element’s position is in the periodic table.