Chemistry C2A

key points:

an atom contains sub-atomic particles: 

• a central nucleus of protons and neutrons
• electrons, which orbit the nucleus

an element's mass number=total number of protons + total number of neutrons per atom. an element's atomic number = number of protons in an atom.

electrons are arranged around the nucleus in shells, which represent energy levels: shell 1 always has 2 electrons; shell 2 has 8 electrons.

electron notation shows the arrangement of electrons in the shells in an element.

• magnesium is 2,8,2.

key points:

ionic bonding- attraction between oppostiely charged ions.

metal atoms lose electrons to form positive ions. non-metal atoms gain electrons to form negative ions.

ionic compounds- 

• giant ionic lattices
• solids at room temperature (high melting points)
• conduct electricity when molten or dissolved

alkali metal- group 1 of the periodic table. reacts losing one electron to form a positive ion. with non-metals (halogens) alkali metals form salts (ionic compounds).

nano-particle- tiny structure made with special properties due to the precise way in which atoms are arranged.

non-metal atoms can share pairs of electrons to form covalent bonds.

simple molecular compounds (water, methane) with covalent bonds:

• do not conduct electricity
• low melting and boiling points
• gases at room temperature
• solid = brittle or waxy
• often insoluble in water

a halogen (group 7 of the periodic table) exists as a molecule of two covalently bonded atoms.

giant covalent structures (diamond) are macromolecules that:

• very high melting points
• very hard
• do not conduct electricity

smart materials have particular properties:

• photochromic materials react to light
• thermochromic materials respond to changes in temperature
• electroluminescent materials emit light when an alternating current passes through them

key points:

the relative formula mass of a compound or molecule = sum of relative atomic masses of all atoms in its formula.

a mole of a substance is the relative formula mass in grams of that substance.

percentage yield can be used to compare the actual yield of a chemical reaction with the theoretical yield

haber process is a reversible reaction

high atom economy is achieved if a high proportion of the reactants end up as useful products. it is important for sustainable development and to limit costs

reversible reactions can proceed in both directions. they are affected by:

• pressure and temperature
• removal of products and presence of a catalyst

reversible reactions carried out in a closed system will eventually reach equilibrium.

percentage mass of an element is given by-

% mass of an element in a compound = relative atomic mass of the element x 

                                                              no. of atoms of element in the formula

                                                                   relative formula mass 

key points:

collision theory- particles must collide with sufficient energy in order to react.

minimum energy required for a reaction to take place (successful collision) is the activation energy.

rate of reaction can be measured as:

• amount of reactant used up in a set time.
• amount of product formed in a set time.

reactions can be speeded up by increasing:

• temperature
• concentration of a solution
• pressure of a gas
• surface area of a solid
• use a catalyst

key points:

exothermic reactions give OUT energy

endothermic reactions take IN energy

if a reversible reaction is exothermic in one direction, it is endothermic in the opposite direction.

equilibrium is reached at a point when the rate of the reverse reaction balances the rate of the forward reaction

conditions used for the haber process-

• temperature 450 degrees
• pressure 200 atmospheres
• iron catalyst

key points:

when molten or dissolved in water, the ions in ionic compounds are free to move

ions are free to move, passing an electric current through an ionic compound breaks it down into its elements. electrolysis.

electrolysis of sodium chloride (salt) solution makes hydrogen, chlorine and sodium hydroxide. copper can be purified by electrolysis.

during electrolysis:

• negative non-metal ions lose electrons at the positive electrode to form atoms and molecules
• positive metal ions gain electrons at the negative electrode to form atoms

OIL RIG- oxidation is loss 

               reduction is gain - of electrons

key points:

metal oxides and hydroxides are bases and react with acids to form salts

soluble bases are alkalis and these react with acids to make salts

in neutralisation reactions, hydrogen ions and hydroxide ions react to form water.

H+(aq) + OH-(aq) = H20(I)

metals can be reacted with acids to make salts. reactivity series of metals can be used to find out if a metal will react with an acid.

salts from acids:

• sulfuric acid = sulfates
• nitric acid = nitrates
• hydrochloric acid= chlorides

insoluble salts can be made as precipitates when two solutions are mixed together

to remove ion impurities from the water supply, they can be made into insoluble salts.