Exam Guide

Exam guide

Chemical bonds

Chemical bonds are forces that hold the atoms together in a molecule. All atoms are trying to achieve a stable octet The protonts (+) in one nucleus are attracted to the electrons(-) of another atom Electronegativity

Chemical bonding provides the energy necessary to hold two different atoms together as part of a chemical compound.

1. Ionic Bond As the name suggests, ionic bonds are a result of the attraction between ions. Ions are formed when an atom loses or gains an electron. These types of bonds are commonly formed between a metal and a nonmetal 2. Covalent Bond In the case of a covalent bond, an atom shares one or more pairs of electrons with another atom and forms a bond. This sharing of electrons happens because the atoms must satisfy the octet (noble gas configuration) rule while bonding 3. Metallic Bonds A metallic bond is a force that holds atoms together in a metallic substance.

Electronegativity

Electronegativity is the tendency of an atom to attract a pair of electrons in a chemical bond. It is caused by the attractive electrostatic force between the positively charged nucleus and the negatively charged electrons. The more electronegative an atom is, the higher will be the attractive force

How to Find Electronegativity Values

Electronegativity can be quantified using several scales. The most prominent scale is known as the Pauling scale.

Linus Pauling American chemist

1. Covalent Bond A covalent bond is formed when the electronegativity difference between the two atoms is equal to or less than 2. The covalent bond can be of two types – polar and nonpolar. 1.1 Nonpolar Covalent Bond The covalent bond is nonpolar if the electronegativity difference is zero. The following image shows a nonpolar covalent bond between two atoms of A. The electrons are equally shared between the two atoms. Examples: Hydrogen (H2), oxygen (O2), and chlorine (Cl2) 1.2 Polar Covalent Bond The covalent bond is polar if the electronegativity difference is between zero and 2. The following image shows the polar covalent bond between A and B. Here, B is more electronegative than A. It influences the bond by pulling the electron pair. The symbol delta (δ) indicates a partial charge.

Ionic Bond An ionic bond exists when the electronegativity difference is greater than 2. The following image shows the ionic bond between A and B.

Oxidation Number (Oxidation State)

An oxidation number is a number that is assigned to an atom to indicate its state of oxidation or reduction during a chemical reaction. Each atom in a redox reaction is assigned an oxidation number to understand its ability to donate, accept, or share electrons.

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How to Find Oxidation Number The oxidation number of an atom in an ion or compound can be determined using the above rules. Let us look at a few examples. 1. Sulfuric Acid (H2SO4) The oxidation number of hydrogen (H) and oxygen (O) are +1 and -2, respectively. Sulfuric acid is a neutral compound. Let x be the oxidation number of sulfur (S). Therefore, (+1) * 2 + x + (-2) * 4 = 0 Or, 2 + x – 8 = 0 Or, x = +6 2. Nitric Acid (HNO3) The oxidation numbers of hydrogen (H) and oxygen (O) are +1 and -2, respectively. Nitric acid is a neutral compound. Let x be the oxidation number of nitrogen (N). Therefore, +1 + x + (-2) * 3 = 0 Or, +1 + x – 6 = 0 Or, x = +5

3. Potassium Permanganate (KMnO4) The oxidation numbers of potassium (K) is +1 and oxygen (O) is -2. KMnO4 is a neutral compound. Let x be the oxidation number of magnesium (Mn). Therefore, +1 + x + (-2) * 4 = 0 Or, +1 + x – 8 = 0 Or, x = +7 4. Dichromate Ion (Cr2O7^2-) Dichromate is a complex ion. The oxidation number of oxygen (O) is -2. The charge of Cr2O72- is -2. Let x be the oxidation number of chromium (Cr). 2x + (-2) * 7 = -2 Or, 2x -14 = -2 Or, x = +6

3. Potassium Permanganate (KMnO4) The oxidation numbers of potassium (K) is +1 and oxygen (O) is -2. KMnO4 is a neutral compound. Let x be the oxidation number of magnesium (Mn). Therefore, +1 + x + (-2) * 4 = 0 Or, +1 + x – 8 = 0 Or, x = +7 4. Dichromate Ion (Cr2O7^2-) Dichromate is a complex ion. The oxidation number of oxygen (O) is -2. The charge of Cr2O72- is -2. Let x be the oxidation number of chromium (Cr). 2x + (-2) * 7 = -2 Or, 2x -14 = -2 Or, x = +6

3. Potassium Permanganate (KMnO4) The oxidation numbers of potassium (K) is +1 and oxygen (O) is -2. KMnO4 is a neutral compound. Let x be the oxidation number of magnesium (Mn). Therefore, +1 + x + (-2) * 4 = 0 Or, +1 + x – 8 = 0 Or, x = +7 4. Dichromate Ion (Cr2O7^2-) Dichromate is a complex ion. The oxidation number of oxygen (O) is -2. The charge of Cr2O7^2- is -2. Let x be the oxidation number of chromium (Cr). 2x + (-2) * 7 = -2 Or, 2x -14 = -2 Or, x = +6

5. Carbonate (CO3^2-) The oxidation number of oxygen (O) is -2 and the charge on CO3^2- is -2. Let x be the oxidation number of carbon (O). Therefore, x + (-2) * 3 = -2 Or, x – 6 = -2 Or, x = +4 6. Phosphite (PO3^3-) The oxidation number of oxygen (O) is -2 and the charge of PO3^3- is -3. Let x be the oxidation number of phosphorous (P). Therefore, x + (-2) * 3 = -3 Or, x – 6 = -3 Or, x = +3

7. Potassium Perchlorate (KClO4) The oxidation numbers of potassium (K) and oxygen (O) are +1 and -2, respectively. Let x be the oxidation number of chlorine (Cl). KClO4 is a neutral compound. Therefore, +1 + x + (-2) * 4 = 0 Or, 1 + x – 8 = 0 Or, x = +7 8. Potassium Nitrate (KNO3) The oxidation number of potassium (K) and oxygen (O) are +1 and -2, respectively. KNO3 is a neutral compound. Let x be the oxidation number of nitrogen (N). Therefore, +1 + x + (-2) * 3 = 0 Or, 1 + x – 6 = 0 Or, x = +5

CATIONS AND ANIONS

Ion: an atom or molecule with a net electric charge due to the loss or gain of one or more electrons. Cations and Anions are both ions