Chem Notes Igcse

1 January 2017

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.

Chem Notes Igcse Essay Example

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.

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