The Principles Of The Octet Rule, Electronegativity, Polarity

The Chemistry of H2O. Principles of the Octet Rule, Electronegativity, Polarity, Density, and their effect on H2O
Aryeh L. Strauss
Suny Rockland

Atoms are made up of protons, neutrons and electrons. Protons have a positive charge and electrons have a negative charge (neutrons are neutral). The protons are in the nucleus of the atom and the electrons fill shells surrounding the nucleus. The shells closest to the nucleus have the lowest energy level and the shells furthest away have the highest energy levels. The outermost shell with the highest energy level is called the valence shell.

When molecules form the individual atoms typically want to fill its valence shell. For example helium is full with two electrons in its valence shell
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When an atom (gives up or receives electron/s and therefore) has a different amount of electrons than in its natural state the amount of electrons will differ from the protons and is called ionic. When an atom has more electrons than protons it has a negative charge and if it has less electrons than protons it has a positive charge. Positively charged ions are attracted to negatively charged ions to form an ionic bond.

Not all atoms give up or receive electrons to complete its valence electrons when they form molecules. Atoms can share electrons to satisfy the octet rule. This is called a molecular bond. In a molecular bond, the shared electrons create a bond between atoms which is called a bonding pair. Paired atoms which are not shared are called lone pairs.

Electronegativity is the likelihood of an atom to attract an electron pair to itself in a molecular bond. The atoms which are closer to having eight electrons are much more likely to attract electron pairs to themselves and have a much greater electronegativity. The atoms which are least likely to attract electron pairs have a lower electronegativity. If there is a difference in electronegativity the electron is more likely to be near the atom with the greater value and is less likely to be near the atom with the lower value. This creates a polar bond, meaning one atom will have a greater negative charge and one will have a greater positive
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The more mass there is in a given volume, the greater the density. The greater the volume for a given mass, the density is less. This can be represented with the formula density equals mass divided by volume. If the numerator increases which is an increase in mass, density will increase, and if the denominator increases which is an increase in volume, the density will decrease.
Volume of non-liquids can be measured through water displacement. Water is placed in a vessel and the volume is recorded, then the object is placed in the vessel and the final volume is recorded. The final volume minus the initial volume is the volume of the substance. Liquids are measured directly by how much it fills a vessel. The volume of gas is the total volume of the vessel.

Density varies in the different physical states; solids, liquids, and gases. Typically a substance in its solid state is denser then in its liquid state. The reason is, liquid molecules aren’t held as tightly together and are moving at a faster rate (as in the solid state) so they spread out more, hence the volume is greater. The density of gas is even less since gas molecules don’t conform to a given shape and will expand to the size of its

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