Chemistry module

• what are the 3 main types of chemical bonds ?

  ionic covalent metallic
• define ionic bonding

  electrostatic attraction between positive and negative ions
• define covalent bonding

  electrostatic attraction between a shared pair of electrons and the nuclei
• define metallic bonding

  electrostatic attraction between the positive metal ions and the sea of delocalised electrons
• why does giant ionic lattics conduct electricity when liquid but not when solid ?

  in solid state the ions are in fixed positions and thus cannot move. when they are in liquid state the ions are mobile and thus can freely carry the charge
• giant ionic lattics have high or lowe melting and boiling point ?

  they have a high mp and bp because a large amount of energy reuired to overcome the elctrostatic bonds
• what are the types of covalent structure ?

  simple molecular lattice giant covalent lattice
• why do simple molecular structure have low melting and boiling point ?

  small amount of energy is enough to overcome the intermolecular forces
• can simple molecular structures conduct electricity

  nope
• why do simple molecular structures not conduct electricity ?

  they have no free charged particles to move around
• examples of giant covalent structures

  diamond graphite silicon dioxide
• properties of giant covalent structures

  high melting and boiling point non conductors of electricity except graphite insoluble in polar and non polar solvents
• how does graphite conduct electricity

  delocalised electrons present between the layers are able to move freely carrying the charge
• why do giant covalent structures have high melting and boiling point ?

  strong covalent bonds within the molecules need to be broken which requires a lot of energy
• what shape has 2 bonding pairs and 0 lone pairs ? what is the angle ?

  linear, 180 Cl-Be-Cl
• what shape has 2 bonding pairs and 2 lone pairs ? what is the angle ?

  bent, 104.5 H2O
• what shape has 3 bonding pairs and 0 lone pairs ? what is the angle ?

  trigonal planar, 120 BF3
• what shape has 3 bonding pairs and 1 lone pairs ? what is the angle ?

  Triangular pyramid, 107 NH3
• what shape has 4 bonding pairs and 0 lone pairs ? what is the angle ?

  Tetrahedral, 109.5 CH4
• what shape has 5 bonding pairs and 0 lone pairs ? what is the angle ?

  Trigonal bipyramid, 180 and 120 PCl5
• what shape has 6 bonding pairs and 0 lone pairs ? what is the angle ?

  Octahedral, 90 SF6
• What are intermolecular forces ?

  These are the forces attracting molecules to eachother.
• What are dipoles ?

  This is when one end of a molecule is slightly positive and one is slightly negative. The positive end of one molecule is attracted to the negative end of another.
• What are the three types of intermolecular forces ?

  Hydrogen bonds, Dipole-dipole, Van der Waals forces
• Rank the intermolecular forces from strongest to weakest

  Hydrogen bond Dipole-dipole Van der Waals
• Where does hydrogen bonding occur ?

  In molecules containing a nitrogen, oxygen or fluorine atom bonded to a hydrogen.
• Where does dipole-dipole forces occur ?

  In molecules containing atoms of differing electronegativity- arranged asymmetrically.
• Where does Van der Waals forces occur ?

  In any atoms or molecules
• Explain how hydrogen bonds are made

  The highly electrognegative N, O or F atom attracts most of the electron cloud away from the hydrogen, leaving the hydrogen slightly positive and other atom slightly negative.
• Explain how dipole-dipole forces are made

  - More electronegative atom attracts greater share of electrons, giving itself a small negative charge and other atom small positive charge. - If molecule is asymmetrical then it gives itself a negative and positive end so molecule has an overall dipole - Molecules like CCl4 and CO2 are symmetrical so they are equally charged
• Explain how Van der Waals are made

  Position of electrons around the nucleus in an atom can be instantaneously unbalanced, leading to a negative and positive region. This creates induced dipoles in neighbouring atoms
• Describe the structure of Diamond C(s)

  - Giant covalent molecule - Each carbon atom joined to 4 other carbon atoms in a tetrahedral arrangement - Strong and rigid structure
• Describe the structure of graphite C(s)

  - Giant covalent molecule - Arranged in layers held by weak Van der Waals forces - Carbon atoms in layers are arranged in hexagons - Delocalised electrons flow along layers but not bewteen them
• Describe the structure of silicon dioxide SiO2

  - Giant covalent structure - Every Si atom is linked to 4 O atoms, in turn every O atom is linked to 2 Si atoms
• Describe the physical properties of diamond C(s)

  - Solid at room temp - High melting and boiling point - insoluble in water and non aqueous solvents - does not conduct electricity - Crystalline - hardest known natural material
• Describe the physical properties of graphite C(s)

  - Solid at room temp - High melting and boiling point - Insoluble in water and non-aqueous solvents - Conducts electricity in one direction only - Feels soft when rubbed because pressure makes the layers move across eachother as the weak bonding is broen
• Describe the physical properties of silicon dioxide SiO2

  - Solid at room temp - High melting and boiling point - Poor conductor of electricity - Insoluble in water and non polar solvents
• What does the law of conversation of energy state ?

  That energy can be converted in form, but not destroyed or created.
• What is the SI unit of energy ?

  Joules (j)
• What is an endothermic reaction ?

  When more energy is needed to break bonds than to make new ones Enthalpy change is positive and heat is taken in from surroundings