Chem Notes Igcse

Topics: Oxygen, Carbon dioxide, Hydrogen Pages: 27 (6684 words) Published: October 11, 2012
IGSCE Chemistry Notes

Oxides are used to determine whether an element is a metal or a non-metal. Most non-metals are classed as acidic oxides. While most metals are classed as basicoxides. Acidic Oxides
* Reacts with water to form acids
* Neutralises alkaline solution to form salt + water
Basic Oxides
* Neutralises acidic solutions to form salt + water
Amphoeteric Oxides
* These are non-metals which display both acidic and basic properties Alkaline Oxides
* Reacts with water to form alkaline solutions
Neutral Oxides
* Do not display either of the acidic or the basic oxides’ properties. 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 Bonding
Definition: 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. If the element is in Group One than the ion will have a 1+ charge If the element is in Group Two than the ion will have a 2+ charge If the element is in Group Three than the ion will have a 3+ charge If the element is in Group Five than the ion will have a 3- charge If the element is in Group Six than the ion will have a 2- charge If the element is in Group Seven than the ion will have a 1- charge There is no charge for group four as they tend to be bonded by covalent bonds. Boiling Points/ Melting Points:

Ionic compounds have high melting points as there are strong intermolecular electrostatic forces of attraction between the oppositely...
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