S3 Chem Notes 07 - Covalent Bond.pdf

S3 Chem Notes 07 - Covalent Bond.pdf -...

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SJC/S.3Chemistry/Covalent Bond (Unit 8) 1 Covalent Bond Part A: Molecules in Compounds and Elements Atoms of non-metallic elements can join together to form molecules . A molecule of an element consists of atoms of the same kind, e.g. Atomicity Description Examples 1 He, Ne, Ar and Kr 2 O 2 , N 2 , F 2 , Cl 2 and Br 2 3 O 3 4 P 4 8 S 8 Molecules of compounds consist of atoms of different kinds. For examples, ammonia NH 3 , methane CH 4 and carbon dioxide CO 2 are all molecules. Question 1: Explain why noble gases exist as monoatomic molecules. ____________________________________________________________________________________________ ____________________________________________________________________________________________ Question 2: Consider the substances listed below: ammonia, carbon dioxide, chlorine, neon, potassium chloride Diagrams I, II and III below show the arrangements of particles, which can be atoms, ions or molecules. For each diagram, choose from the above list ONE substance which has the arrangement of particles as shown below at room temperature and pressure. ____________________________________________________________________________________________ Part B: Formation of Molecules When atoms of the non-metals combine, they tend to share their outermost shell electrons in order to attain the nearest noble gas electronic arrangement. Hence, covalent bond is formed. Covalent bond is the strong directional electrostatic attraction between the shared electrons (negatively charged) and the two nuclei (positively charged) of the bonded atoms .
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SJC/S.3Chemistry/Covalent Bond (Unit 8) 2 Take a chlorine molecule as an example, A single covalent bond is often represented by a stroke ( ) between the atomic symbols. Apart from electron diagrams, molecules can be represented by molecular formula of a molecule is the formula which shows the actual number of each kind of atoms in one molecule of the substance, i.e. the molecular formula of chlorine is Cl 2 . structural formula of a molecule is the formula which shows how the constituent atoms are joined up, i.e. the structural formula of chlorine is Cl-Cl . Question 3: Explain why fluorine exists as diatomic molecules ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ B-1: Multiple Bonds A bond in which one pair of electrons is shared between two atoms is called a single bond.
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