C1

• atoms elements and compounds

  all substances are made of atoms
• atoms, elements and compounds


  an atom is the smallest part of an element that can exist
• atoms elements and compounds

  compounds are formed from elements by chemical reactions
• atoms, elements and compounds

  chemical reactions always involve the formation of one or more new substances and often involve a detectable energy change
• atoms, elements and compounds

  compounds contain two or more elements chemically combined in fixed proportions
• atoms, elements and compounds

  compounds can only be separated into elements by chemical reactions
• atoms, elements and compounds

  a mixture consists of two or more elements of compounds not chemically combined together. The chemical properties of each substance in the mixture is unchangeable.
• atoms, elements and compounds

  mixtures can be separated by physical processes such as filtration ,crystallisation , simple distillation , fractional distillation and chromatography
• atoms, elements and compounds

  filtration is the process in which an insoluble solid is separated from a liquid. eg- to get sand from a mixture of sand ,salt and water
• atoms, elements and compounds

  crystallisation is the process in which a solid is separated from a solution. eg- to obtain pure crystals of sodium chloride from salt water
• atoms, elements and compounds

  simple distillation is the process in which a solvent is separated from a solution. eg- to get pure water from salt water
• atoms, elements and compounds

  fractional distillation is the process in which a mixture of liquids with different boiling points is separated. eg - to separate the different compounds in crude oil
• atoms, elements and compounds

  chromatography is the process in which substances that move through a medium at different rates are separated. eg- to separate out they dyes in food colouring
• development of atomic model

  before the discovery of the electron, atoms where thought to be tiny spheres that could not be divided. John Daltons theory
• development of the atomic model

  JJ Thomson concluded that atoms weren't solid spheres. His measurements of charge and mass showed that an atom must contain even smaller negatively charged particles (electrons). Creating the plum pudding model which illustrates a ball of positive charge with negative electrons embedded in it.

  
• development of the atomic model

  Ernest Rutherford then changed the atomic model again following his alpha particle scattering experiment ( in which positively charged alpha particles were fired at a thin sheet of gold foil. Some particles passed straight through, others were deflected ) as a result of this Rutherford created the nuclear model: in which a tiny positively charged nucleus is at the centre (where most of the mass is concentrated) with a cloud of negative electrons surrounding it, leaving the majority of the atom as empty space.
• development of the atomic model

  Niels Bohr's atomic model suggested that all electrons were contained within shells that orbit the nucleus at fixed distances
• development of the atomic model

  Rutherford showed that the nucleus can be further divided into smaller particles which each have the same charge as a hydrogen nucleus. These particles were shown to be positive and given the name protons.
• development of the atomic model

  Jamie Chadwick carried out experiments which proved the existence of neutral particles in the nucleus (called neutrons)
• relative electrical charges of subatomic particles

  proton --> +1

  neutron --> 0

  electron --> -1
• relative electrical charges of subatomic particles

  in an atom the number of electrons is equal to the number of protons in the nucleus. Therefore atoms have no overall electrical charge.

  the number of protons in an atom of an element is its atomic number. All atoms of an element have the same number of protons. Whilst different elements atoms all have different number of protons
• size and mass of atoms

  atoms are very small having a radius of around 0.1nm (1 x 106^-10 m )

  radius of a nucleus is around 1/10 000 of that of an atom
• size and mass of atoms

  almost all of the mass in an atom is from the nucleus

  proton --> 1

  neutron --> 1

  electron-->very small
• size and mass of atoms

  the sum of the protons and neutrons in an atom is its mass.

  atoms of the same element can have different numbers of neutrons: these are called isotopes
• relative atomic mass


  RAM of an element is an average value that includes possible isotopes of an element.

  RAM = sum of (isotope abundance x isotope mass number) / sum of abundances of all the isotopes
• electronic structure


  electrons in an atom occupy the lowest available energy levels . The electronic structure of an atom can be represented by numbers or by a diagram

  eg- electronic structure of sodium is 2,8,1 or

  
• periodic table


  elements in the periodic table are arranged in order of atomic (proton) number and so that elements with similar properties are in columns (groups).

  Elements in the same group in the periodic table have the same number of electrons in their outer shell giving them similar chemical properties.
• development of the periodic table

  before the discovery of protons, neutrons and electrons scientists attempted to classify the elements by arranging them in order of atomic weights.

  The early periodic tables were incomplete and some elements were placed in inappropriate groups if the order of atomic weight was followed.
• development of the periodic table

  Mendeleev overcame these problems by leaving gaps for undiscovered elements and in some places changed the order based on atomic weight.Elements properties were predicted by Mendeleev were discovered and filled the gaps. Knowledge of isotopes made it possible to explain how the order based on atomic weights was not always correct.
• metals and non-metals


  elements that form positive ions are metals

  elements that from negative ions are non-metals.
• metals and non-metals


  the majority of elements are metals which are found to the left and towards the bottom of the periodic table.

  non-metals are found towards the right and top of the periodic table.
• metals and non-metals 


  metals at the top pf the periodic table don't have many electrons in their outer shell able to be lost whereas metals at the bottom have outer electrons far from the nucleus so feel a weaker attraction. Both these effects means that not much energy is needed to remove the electrons so is therefore easier for the atom to react to form a positive ion with a full outer shell
• metals and non-metals


  non-metals either have lots of electrons in their outer shell or the outer shell is close to the nucleus so feel a strong attraction. This means it is harder for them to form a positive ion through losing electrons. Instead they can achieve a full outer shell through gaining or sharing electrons.
• metals and non-metals


  metals have metallic bonding which causes them all to have similar physical properties : hard, malleable, good conductors of heat and electricity, high boiling and melting points.
• metals and non-metals


  non-metals don't have the same physical properties as metals so are: dull looking, brittle, can be non-solid, don't conduct electricity and have low densities
• group 0 


  noble gases are unreactive and do not easily form molecules as their atoms have stable arrangements of electrons.

  They have 8 electrons in their outer shell except for helium which only has 2
• group 1

  alkali metals have similar properties due to their 1 outer electron.

  as you go down group 1 reactivity increases whilst boiling and melting points decrease, RAM also increases.
• group 1


  reaction with water:

  react vigorously to produce hydrogen gas and metal hydroxides

  sodium + water --> sodium hydroxide + hydrogen
• group 1 


  reaction with chlorine:

  react vigorously when heated in chlorine gas to form white metal chloride salts

  sodium + chlorine --> sodium chloride
• group 1 


  reaction with oxygen:

  react with oxygen to form a metal oxide

  lithium + oxygen --> lithium oxide