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Chemical Chameleon

Fun of Chemistry :) 

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Learn The Oxidation Number

QUESTION 1

What is the oxidation state of chromium in Cr²⁺?

SOLUTION

For a simple ion such as this, the oxidation state equals the charge on the ion: +2 (by convention, the + sign is always included to avoid confusion)

What is the oxidation state of chromium in CrCl₃?

This is a neutral compound, so the sum of the oxidation states is zero. Chlorine has an oxidation state of -1 (no fluorine or oxygen atoms are present). Let n equal the oxidation state of chromium:

n + 3(-1) = 0

n = +3 

The oxidation state of chromium is +3.

QUESTION 2

What is the oxidation state of chromium in Cr(H₂O)₆³⁺?

SOLUTION

This is an ion and so the sum of the oxidation states is equal to the charge on the ion. There is a short-cut for working out oxidation states in complex ions like this where the metal atom is surrounded by electrically neutral molecules like water or ammonia.

The sum of the oxidation states in the attached neutral molecule must be zero. That means that you can ignore them when you do the sum. This would be essentially the same as an unattached chromium ion, Cr³⁺. The oxidation state is +3.

What is the oxidation state of chromium in the dichromate ion, Cr₂O₇^2-?

The oxidation state of the oxygen is -2, and the sum of the oxidation states is equal to the charge on the ion. Don't forget that there are 2 chromium atoms present.

                                                                                2n + 7(-2) = -2

                                                                                            n = +6

QUESTION 3

What is the oxidation state of copper in CuSO₄?

SOLUTION

Unfortunately, it isn't always possible to work out oxidation states by a simple use of the rules above. The problem in this case is that the compound contains two elements (the copper and the sulfur) with variable oxidation states.

In cases like these, some chemical intuition is useful. Here are two ways of approaching this problem:

·         Recognize CuSO₄ as an ionic compound containing a copper ion and a sulfate ion, SO₄^2-. To form an electrically neutral compound, the copper must be present as a Cu²⁺ ion. The oxidation state is therefore +2.

·         Recognize the formula as being copper(II) sulfate (the (II) designation indicates that copper is in a +2 oxidation state, as discussed below).

About Periodic Table

Across the periodic table (from left to right)
Increases:

1. Electronegativity
2. Electron Affinity
3. Ionization Energy
4. Effective Nuclear Charge

Decreases:

1. Atomic Radius
2. Ionic Radius

Down The Group (from up to down)

Increases:

1. Atomic Radius
2. Ionic Radius

Decreases:

1. Electronegativity
2. Electron Affinity
3. Ionization Energy
4. Effective Nuclear Charge

Fun Facts About Chemistry

Chemistry is a fascinating science, full of unusual trivia! Here are some fun and interesting chemistry facts for you.

• The only elements that are liquid at room temperature are bromine and mercury. However, you can melt gallium by holding a lump in the warmth of your hand.
  
  
• Unlike many substances, water expands as it freezes. An ice cube takes up about 9% more volume than the water used to make it.

• If you pour a handful of salt into a full glass of water, the water level will actually go down rather than overflowing the glass.
• There is about 1/2 lb or 250 g of salt (NaCl) in the average adult human body.
• A pure element can take many forms. For example, diamond and graphite both are forms of pure carbon.
  
  
• The chemical name for water (H2O) is dihydrogen monoxide.
  
  
• The only letter that doesn't appear on theperiodic table is J.
  
  
• Lightning strikes produce O3, which is ozone, and strengthen the ozone layer of the atmosphere.
  
  
• The only two non-silvery metals are gold andcopper.
  
  
• Although oxygen gas is colorless, the liquid and solid forms of oxygen are blue.
  
  
• The human body contains enough carbon to provide 'lead' (which is really graphite) for about 9,000 pencils.
  
  
• Hydrogen is the most abundant element in the universe, while oxygen is the most abundant element in the earth's atmosphere, crust, and oceans (about 49.5%).
  
  
• The rarest naturally-occurring element in the earth's crust may be astatine. The entire crust appears to contain about 28 g of the element.
  
  
• Hydrofluoric acid is so corrosive that it will dissolve glass. Although it is corrosive, hydrofluoric acid is considered to be a 'weak acid'.
• One bucket full of water contains more atoms than there are bucketfuls of water in the Atlantic ocean.
  
  
• Approximately 20% of the oxygen in the atmosphere was produced by the Amazon rainforest.
  
  
• Helium balloons float because helium is lighter than air.
  
  
• Bee stings are acidic while wasp stings are alkaline.
  
  
• Hot peppers get their heat from a molecule called capsaicin. While the molecule acts as an irritant to mammals, including humans, birds lack the receptor responsible for the effect and are immune to the burning sensation from exposure.
  
  
• Dry ice is the solid form of carbon dioxide, CO2.
  
  
• Liquid air has a bluish tint, similar to water.