chemisty module 2

• what is relative atomic mass

  the weighted mean mass of an atom of an element when compared to 1/12 of the mass of 1 atom of c-12
• what is the relative isotopic mass

  the mass of an atom of an isotope when compared with 1/12 of the mass of one atom of c-12
• what does the weighted mean mass take into account

  - relative mass

  - percentage abundance of each isotope
• what is an acid

  proton donor (releases H+ ions in water)
• what is a strong acid

  a proton donor that fully dissociates in a solution
• what is a weak acid

  a proton donor with partially dissociates in a solution
• what is a salt

  a compound formed when the h+ ion from an acid is replaced by a metal
• what is a base

  a proton accepter
• what is an alkali

  a soluble base that realeases OH- ions in a solution
• what is the test for H+

  - add blue litmus papwer

  - positive result turns red
• what is the test for OH-

  - add red litmus paper

  - posivite result turns blue
• what is the test for carbonate ions

  - add nitric acid to form CO2

  - bubble through limewater
• what is the sulfate test

  - add barium nitrate

  - postive result forms a white precipitates
• what is the halide test

  - add silver nitrate

  - Ag+ + x = AgX
• what is a positive result for bromide ions

  - cream precipitate

  - soluble in concentrated ammonia
• what is positive result for chloride ions

  - white precipitate

  - soluble in dilute ammonia
• what is a postive result for iodide ions

  - yellow precipitate

  - insoluble in ammonia
• what is the test for ammonium

  - add NaOH and heat

  - if ammonia is produced damp litmus paper will turn from red to blue
• what is metallic bonding

  the electrostatic attraction between positive metal ions and delocalised electrons
• what is ionic bonding

  the electrostatic attraction between oppositely charged ions
• what is a covalent bond

  the strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
• what is a dative covalent bond

  a shared pair of electrons in which the bonded pair has been provided by one of the bonding atoms only
• what is the melting point of metals

  - high melting point

  - lots of energy is required to overcome the strong electrostatic forces of attraction between oppositely charged ions
• can metals conduct electricity

  yes as there are delocalised electrons that are free to move through the structure and carry a charge
• why are metallic bonds insoluble

  metallic bonding is stronger than the attraction of the polar water molecules
• how does the metallic structure allow metals to be malleable and ductile

  - ions slide past eachother

  - delocalised electron move to prevent the layer breaking off
• are ionic compounds soluble or insoluble

  soluble in water as the water molecules are attracted to the charged ions
• explain the electrical conductivity of ionic compounds

  - dont conduct when solid as the ions are in a fixed position so no mobile ions

  - can conduct when molten as aqueous as the ions are no longer in a fixed positions so there are mobile ions
• what are the properties of a giant covalent lattice

  - high melting and boiling points

  - insoluble in most solvents are bonds too strong to be broken
• what are some properties of graphite

  - 3 bonds

  - spare electron is delocalised between the layers

  - weak forces of attraction between the layer

  - can conduct electricity
• what is the electron repulsion theory

  - electron pairs determine the shape

  - electrons repel one another so are far apart
• what is electronegativity

  the ability of an atom to attract the bonding pair of electrons towards itself in a covalent bond
• why aren't noble gases included in electronegativity

  as they dont form compounds
• what happens to the electronegativity across a period

  - same number of shells

  - atomic radius decreases

  - more protons

  - greater nuclear attraction

  - electronegativity increases
• what happens to the electronegativity down a group

  - more shells

  - atomic radius increases

  - more shielding

  - weaker nuclear attraction

  - electronegativity decreases
• what is a permanent dipole

  when covalently bonded atoms have different electronegativities
• what is a london force

  weak intermolecular forces that exist between all molecules
• what are permanent dipole-dipole interactions

  weak intermolecular forces that exist between the permanent dipoles in different polar molecules
• what are examples of hydrogen bonds

  N, O and F
• what increases the strength of london forces

  - more electrons

  - larger the instantaneous and induced dipoles

  - greater the induced dipole-dipole interactions

  - stronger the attractive forces