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Chemistry assignment

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3.1
a) Valence electron:
Valence electrons are the electron in the outermost electron shells of an atom. They are generally the electrons involved in chemical reactions and bonding with other atoms.

b) Lewis electron:
It is a structural demonstration of a molecule where you can use dots to show the position of the electron around the atoms and lines.
c) Octet rule:
It is referring to the principle that bonded atoms share their eight outer electrons. There rule of the octet is sometimes broken.

d) Cations/Anions:
It is an ionic species with a positive charge, example of Cation/Anions:
Anion is an ionic species having a negative charge.

e) Electronegativity:
It is a property of an atom which increases with its tendency to attract the electron of a bond.

f) Polar covalent bond:
Polar covalent bonds act between two atoms; the electrons forming the bond are unequally spread. These bonds can lead to the formation of a weak bond which is called hydrogen. Also it will cause the molecule to have an electrical dipole moment, where one end will be positive and the other end negative.

G) Non- polar covalent bond:
Electrons are shared between elements having a difference in electronegativity of less than 0.5. It does not involve the sharing of pair of electrons.

H) Vander Waals forces:
Van der Waals forces are the weak forces which contribute to intermolecular bonding. They can be induced or permanent. If the atoms are bigger, the Van der Waals forces will be bigger.

I) Hydrogen bond:
It is referred to when an interaction occurs between a hydrogen atom with a electronegative atom from a dissimilar chemical group. Also it is stronger than a Vander Waals forces, but weaker than ionic and covalent bonds.

3.2 List FOUR properties of ionic compounds.
1. High melting point: 800°C
2. They form crystals
3. Non-conductive in its solid state
4. They have higher enthalpies of fusion and vaporization than molecular compounds.

3.3 List FOUR properties of covalent compounds.
1. They tend to be more flammable than ionic compounds.
2. Many covalent compounds don’t dissolve well in water.
3. They are soft and relatively flexible.
4. Most of them have relatively low melting and boiling points.

4.4
O2  Non-polar: it is non-polar because the two atoms have an equal attraction for electrons, they share the bonding electron and also a nonpolar covalent is formed.
HF  Polar: the covalent bond electrons are displaced towards the electronegative fluorine.
Ch3Br  Polar: the difference in electronegativity between C and Br makes it a polar molecule.
SCL3  Polar: it is a polar molecule because the central atom has a lone pair.

4.5
a)
ii)
Surface tension water molecule it is formed by two hydrogen which are covalently bonded to an oxygen molecule. When the dipole is created within the molecules, H is a little positive and O negative. This happens because the covalent bond shares electrons unequally between molecules and the electrons are drawn towards the oxygen. When water molecules interact they form hydrogen bond, on either side of the negative hydrogen and positive oxygen of an adjacent molecule. The surface tension of water is attracted by the inter-molecular.
Boiling point the boiling point of water if 100°C or 212°F, it has boiling points that are high, due to the hydrogen bonds between water molecules which have to be broken for the occurrence of phase transition. Boiling point of water without hydrogen bonds would be around -150°C.

b)
Lone pairs of electrons are much more effective at resisting other electrons than bonding pairs; this is according to VSEPR theory. Also there are four electron pairs, which 3 of them are bonding and 1 lone pair, so the bonding angle is 107.3°. The electrons give a tetrahedral arrangement but the molecule has a pyramidal shape, this is due to the lone pair.

Sources: http://errantscience.com/blog/2013/07/24/water-surface-tension/ http://chemistry.about.com/

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