11 chemistry

• The law of conservation of mass states that the total mass of the reactants must equal the total mass of the products in a chemical reaction.
• Mendeleev's Periodic Law states that the properties of elements are a periodic function of their atomic masses
• Moseley showed that atomic number is a more fundamental property of an element than its atomic mass
• The Modern Periodic Law states that the physical and chemical properties of elements are periodic functions of their atomic numbers
• Types of elements include s-, p-, d-, and f-blocks
• Main group elements or representative elements include s- and p-block elements
• 1. block elements include Group-1 (Alkali metals) and Group-2 elements (Alkaline earth metals) with ns1 and ns2 outermost electronic configurations respectively
• 1. block elements belong to groups 13 to 18 with outermost electronic configuration ns2 np1-6
• 1. block elements (Transition elements) have outer electronic configuration (n-1) d1-10 ns1-2
• 1. block elements (Inner-transition Series) include Lanthanoids and Actinoids with characteristic outer electronic configurations (n-2) f1-14 (n-1) d0-1 ns2
• Noble gases in Group 18 have outermost electronic configuration ns2 np6, except for Helium which has 1s2 configuration
• Atomic radius is the distance from the nucleus to the outermost shell of electrons
• In a period, atomic radius decreases from left to right, while in a group, it increases from top to bottom
• Covalent radius is half the inter-nuclear distance between two covalently bonded atoms
• Van der Waals' radius is half the inter-nuclear separation between atoms in neighboring molecules
• Metallic radius is half the distance between the nuclei of adjacent metal atoms in a lattice
• Ionic radius is the effective distance from the nucleus of an ion up to which it influences its electron cloud
• Cations are smaller, and anions are larger than the parent atom
• Ionisation enthalpy is the enthalpy change when an electron is removed from a gaseous atom or ion
• Ionisation enthalpy generally decreases top to bottom in a group and increases left to right in a period
• Electron gain enthalpy is the enthalpy change when an electron is added to a gaseous atom or ion
• Electron gain enthalpy increases left to right in a period and decreases top to bottom in a group
• Electronegativity is the relative tendency of an atom to attract shared electrons in a molecule
• Electronegativity increases left to right in a period and decreases top to bottom in a group
• Valence electrons are the electrons in the outermost shell of an atom
• Valency is the number of atoms that combine with one atom of an element
• Valency first increases then decreases left to right in a period and remains constant top to bottom in a group
• Electropositive or metallic character is the tendency of an element to lose electrons and form cations
• Electropositive character decreases left to right in a period and increases top to bottom in a group
• Electronegative character is the tendency of an element to accept electrons and form anions
• Electronegative character increases left to right in a period and decreases top to bottom in a group
• Electro-negativity or non-metallic character:

  • The tendency of an element to accept electrons to form an anion is called its non-metallic or electronegative character
  • Elements with high electro-negativity have a higher tendency to gain electrons and form anions
  • Elements in the upper right-hand portion of the periodic table are electro-negative or non-metallic in nature
• Reactivity of metals:

  • In a period, the reactivity of metals decreases from left to right as the tendency to lose electrons decreases
  • In a group, the reactivity of metals increases from top to bottom as the tendency to lose electrons increases
• Periodicity of electro-negativity:

  • In a period, electro-negativity increases from left to right
  • In a group, electro-negativity decreases from top to bottom
• Thermal stability of carbonates of alkali and alkaline earth metals:

  • Lithium carbonate (LiCO3) is stable towards heat, while the carbonates of other alkali metals decompose on heating
  • The decomposition temperature for alkaline earth metal carbonates increases as we go down the group
• Solubility of alkaline earth metal hydroxides and sulphates:

  • In a group, the solubility of alkaline earth metal hydroxides and sulphates in water increases down the group from Beryllium to Barium
• Basic strength of alkaline earth metal hydroxides:

  • In a group, the basic strength of alkaline earth metal hydroxides in water increases down the group from Beryllium to Barium
• Reactivity of non-metals:

  • In a period, the reactivity of non-metals increases from left to right as the tendency to gain electrons increases
  • In a group, the reactivity of non-metals increases from top to bottom as the tendency to gain electrons decreases
• Solubility of alkali metal carbonates and bicarbonates:

  • In a group, the solubility of alkali metal carbonates and bicarbonates in water increases down the group from Lithium to Caesium
• In single-celled organisms, substances can easily enter the cell due to a short distance, while in multicellular organisms, the distance is larger because of a higher surface area to volume ratio