Chemistry

• Atoms:


  . Radius of 0.1 nanometers

  . Nucleus contains protons and neutrons

  . Nucleus had a positive charge

  . Electrons move around Nucleus in electron shells
• Atoms:

  Proton: charge = +1

  Neutron: charge = 0

  Electron: charge = -1
• Atoms:

  Proton: relative mass = 1

  Neutron: relative mass = 1

  Electron: relative mass = very small (0)
• Atoms:

  Number of protons is same as number of electrons. This means atoms are neutral - they have no charge. The charge cancels out.
• Atoms:

  Atomic number = how many protons there are. (Number below element symbol)

  Atomic mass = total number of protons and neutrons. (Number above element symbol).

  To get number of neutrons - subtract Atomic number from Atomic mass.
• Elements:

  Elements consist of atoms with the same atomic number.
• Elements:

  Number of protons decide what type of atom it is. E.g. 1 atom is hydrogen.

  If a substance only contains atoms with the same number of protons its called an element.

  There are about 100 different types of element.
• Elements: isotopes


  They are different forms of the same element- with the same number of protons but a different number of neutrons. E.g. carbon-12 and carbon-13
• Compounds:

  Elements/atoms join together to make compounds. When Elements react, atoms combine with other atoms to form compounds.

  They are formed from 2 or more Elements. They are held together by chemical bonds.
• Compounds: chemical bonds


  Making bonds involves atoms giving away, taking or sharing electrons. The nuclei of the atoms aren't affected.
• Compounds:

  Covalent bonding - each atom shares an electron with another atom. Formed from non-metals.

  E.g. carbon monoxide
• Mixtures:


  Unlike a compound, there is no chemical bond between the different parts of a mixture.
• Mixtures:

  Parts if a mixture can be either elements or compounds. They can be separated by physical methods.

  Physical methdods:

  . Filtration

  . Crystallisation

  . Simple distillation

  . Fractional distillation

  . Chromatography
• Mixtures:

  Air is a mixture of gasses: nitrogen, oxygen, carbon dioxide and argon
• Mixtures: chromatography 


  Used to separate different dyes in an ink.
• The atomic model:

  .Early 1800s - John Dalton- solid spheres

  .1897 - JJ Thomson - plum pudding model

  .1909 - Ernest Rutherford - nuclear model

  . Next - Niels Bohr - atoms contained in shells

  . James Chadwick - neutrons
• The atomic model: John Dalton 


  He described atoms as solid spheres and that different spheres made up different elements.
• The atomic model: JJ Thompson

  Atoms aren't solid spheres. His measurements of charge and mass showed that an atom has to contain negatively charged particles (electrons). Known as the Plum Pudding Model

  
• The atomic model: Rutherford

  He conducted the alpha particle scattering experiments. - they fired positively charged alpha particles at an extremely thin sheet of gold.

  Most particles wen through the gold sheet but some were deflected more than expected.

  This lead to the nuclear model of the atom. There are:

  • Tiny positively charged nucleus at centre
  • Cloud of negative electrons around
  • Most of the atom is empty

  
• The atomic model: Bohr

  His nuclear model suggested the electrons were contained in a shell. The electrons orbit in fixed shells at a fixed distance from the nucleus.
• The atomic model: further experiments

  Further experiments after Bohr showed that the nucleus can be divided into smaller particles, each having the same charge as a hydrogen nucleus. These were named protons.
• The atomic model: James chadwick

  20 years after the acceptance of atoms having nuclei, he carried out an experiment which provided evidence for neutral particles = neutrons.
• Relative atomic mass:

  Isotopes - different forms of the same element which have the same number of protons but a different number of neutrons. So they have different mass numbers.
• Relative atomic mass:

  = sum of (isotope abundance × isotope mass number) ÷ sum of abundances of all the isotopes
• Electronic structure:

  When the outer shell of the atom is not full, this makes the atom want to react to fill it.
• Electronic structure:

  1st shell: 2

  2nd shell: 8

  3rd shell: 8
• Electronic structure: work out

  Example:

  Nitrogen atomic number is 7. This means it has 7 protons so therefore 7 electrons.

  So the electronic structure for nitrogen is 2,5
• In the early 1800s, what were elements arranged by?

  Atomic weight
• What are the 2 ways to categorise elements?

  Their physical and chemical properties.

  Their atomic weight.
• When were protons and electrons discovered and what did this mean?

  They were discovered in the 20th century and it meant elements could now be arranged by atomic number.
• Dmitri Mendeleev


  In 1869, he took 50 known elements and arranged them into a table of elements with various gaps. He ordered them mostly in atomic weight.
• Dmitri Mendeleev: gaps


  He left gaps in the periodic table to make sure similar properties stayed in the sane groups. He could then predict what the undiscovered elements were and when they were discovered they fitted the pattern.
• How many elements are there?

  Around 100
• How are elements laid out?

  In order of increasing atomic number.
• Modern periodic table:


  Elements with similar properties form columns - they are called groups
• What does the group number tell you in the periodic table?

  Tells you how many electrons there are on the outer shell
• What are the rows in the periodic table called?

  Periods. Each new period represents another full shell of electrons
• What are metals?


  They are elements which form positive ions when they react. Most elements are metals.
• Where are metals on the periodic table?

  The left
• Where are non metals in the periodic table?

  The right