Chemistry Gateway (OCR)

1. Atomic Structure and the Periodic Table

Atomic Structure

• Atoms are the basic building blocks of matter, consisting of three main subatomic particles:

  • Protons: Positively charged particles found in the nucleus.

  • Neutrons: Neutrally charged particles found in the nucleus.

  • Electrons: Negatively charged particles found in electron shells or orbitals around the nucleus.

• Atomic Number: The number of protons in an atom, which defines the element.

• Mass Number: The total number of protons and neutrons in an atom.
  Formula:
  Mass Number = Number of protons + Number of Neutrons

The Periodic Table

• The Periodic Table organizes elements by increasing atomic number and groups elements with similar properties in columns.

• Elements in Group 1 (alkali metals) have one electron in their outer shell, while Group 7 elements (halogens) have seven electrons in their outer shell.

• The Periodic Law states that elements with similar properties occur at regular intervals when arranged by atomic number.

2. Bonding and Structure

Ionic Bonding

• Ionic bonds form when electrons are transferred from one atom to another. This typically happens between metals and nonmetals.

• The metal atom loses one or more electrons, forming a positive ion (cation), while the nonmetal atom gains those electrons, forming a negative ion (anion)
  Example: In the formation of sodium chloride (NaCl), sodium (Na) loses an electron and chlorine (Cl) gains it:

  

 These oppositely charged ions are attracted to each other, forming an ionic bond.

Covalent Bonding

• Covalent bonds form when atoms share electrons, typically between nonmetals. This results in the formation of molecules.
  
  Example: In a water molecule (H₂O), two hydrogen atoms each share one electron with an oxygen atom, creating covalent bonds:

Metallic Bonding

• Metallic bonds occur between metal atoms, where electrons are shared in a "sea of electrons" that move freely between positive metal ions.

• This gives metals their characteristic properties such as electrical conductivity and malleability.

3. Quantitative Chemistry

The Mole

• The mole (mol) is a unit used to count particles at the atomic and molecular scale. One mole of any substance contains Avogadro’s number of particles (atoms, molecules, ions, etc.).
  Avogadro’s constant:

  

Molar Mass

• The molar mass of a substance is the mass of one mole of its particles (atoms or molecules), typically expressed in grams per mole (g/mol).
  Formula:
  Molar Mass = Mass of Substance / Amount of Substance (mol)

Concentration

• Concentration is the amount of solute dissolved in a given volume of solution.
  Formula:
  Concentration (mol/dm3) = Amount of Solute (mol)/Volume of Solution (dm3)

4. Chemical Changes

Reactions and Reaction Types-

• Acid-Base Reactions: In these reactions, an acid reacts with a base to produce water and a salt. This is also known as neutralization.
  
  Example:

  

• Oxidation and Reduction: Oxidation involves the loss of electrons, while reduction involves the gain of electrons. These two processes occur together in redox reactions.
  
  Example: In the reaction of sodium and chlorine:

  

5. Energy Changes in Reactions

Exothermic and Endothermic Reactions

• Exothermic Reactions release energy, usually in the form of heat.
  
  Example: Combustion of methane:

  

• Endothermic Reactions absorb energy from their surroundings.
  
  Example: The thermal decomposition of calcium carbonate:

  

Activation Energy

• Activation Energy (Eₐ) is the minimum energy required for a reaction to occur. It can be influenced by temperature and catalysts.
  Formula (Arrhenius equation):
                     

  

• Where:

  • k = Rate constant

  • A = Frequency factor

  • Eₐ = Activation energy

  • R = Gas constant

  • T = Temperature (Kelvin)

6. Organic Chemistry

Basic Organic Compounds

• Hydrocarbons: Compounds made up of hydrogen and carbon atoms. They can be classified into alkanes (saturated hydrocarbons), alkenes (unsaturated hydrocarbons), and alkynes.

  • Alkanes: Saturated hydrocarbons, e.g., methane (CH₄), ethane (C₂H₆).

  • Alkenes: Unsaturated hydrocarbons containing double bonds, e.g., ethene (C₂H₄).

  • Alkynes: Unsaturated hydrocarbons containing triple bonds, e.g., ethyne (C₂H₂).

Functional Groups

• Alcohols (e.g., ethanol, C₂H₅OH) and carboxylic acids (e.g., acetic acid, CH₃COOH) are important classes of organic compounds with specific functional groups.
  
  General Formula for Alcohols:
                                                                R - OH
  General Formula for Carboxylic Acids:
                                                               R - COOH

7. Chemistry in Industry

Industrial Applications of Chemistry

• Chemistry is essential in industries such as pharmaceuticals, energy, and materials science. Key areas include:

  • The Haber Process for the production of ammonia.

  • The Contact Process for the production of sulfuric acid.

  • Catalysis in the production of various chemicals.

Example:
The Haber Process for ammonia synthesis: