Atomic structure

• What is an atom?


  The smallest part of an element that can exist.
• What is an element?


  A substance of only one type of atom.
• How are the elements listed?

  In the periodic table.
• Approximately how many elements are there?

  Approximately 100.
• Based on their properties, elements are classified into two groups. What are these groups?


  Metals and non-metals.
• To form new substances, elements can combine through chemical reactions. What are these new substances called?


  Compounds.
• What is a compound?


  Two or more elements that are chemically combined in fixed proportions that can be represented by a formulae.
• Do compounds have the same properties as their constituent elements.


  No, because their electrons rearrange.
• What is a mixture?


  Two or more elements that are not chemically combined together.
• Does a mixture have the same chemical properties as its constitute materials?


  Yes.
• What are the five methods in-which mixtures can be separated? Do they involve chemical reactions?

  Filtration, chromatography, crystallisation, both simple and fractional distillation. They do not involve chemical reactions.
• Describe and explain simple distillation. 


  Simple distillation is used to separate liquid from a solution. The liquid is heated with a bunsen burner, boiling off and then condensing when reaching the condenser, which is cooled by a cooling glove. The thermometer will read the boiling point of the pure liquid. The vapour is now a liquid so it will travel down the condenser into a flask which will only contain the pure liquid.
• Describe and explain evaporation.


  This is a technique fore the separation of a solid dissolved in a solvent from the solvent (Like salt from water).

  The solution is heated using a bunsen burner until all the solvent has evaporated; the solids remain in the evaporating dish.
• Describe and explain crystallisation


  Gently heat the solution in an evaporating dish so some of the solvent can evaporate. This makes the solution more concentrate. When the it reaches the point of crystallisation (crystals start to visibly form) stop heating the dish so they can dry. The salts should start forming crystals as the cold decreases solubility creating a highly concentrated solution. Filter the crystals out using filter paper leaving them in a warm place to dry.
• Describe and explain fractional distillation.


  This is a technique for separating a mixture of liquids with different boiling points. The apparatus has fractionating columns placed on top of a heating flask. The columns contain glass beads the help separate the columns. Mixtures are repeatedly heated and vapour used. The column is hot at the bottom and cold at the top so that liquids can condense at different heights.
• Describe and explain filtration. 


  Filtration separates an insoluble solid (called a residue) suspended in a liquid. The residue is caught in the filter paper as the particles are too big to fit through the holes of the paper. The filtrate is the substance that comes through the filter paper. Apparatus: filter paper + funnel.
• Describe and explain chromatograph.


  Chromatography is used to separate a mixture of substances dissolved in a solvent. In paper chromatograph, a piece of paper with a spot containing a mixture in places in a beaker with a solvent. The bottom of the paper has to be in contact with the solvent. The solvent will slowly start to rise separating the spot (mixture) into few spots (components).
• Describe the plum-pudding model.

  The atom is a ball of positive charge (the pudding) with negative electrons embedded in it (the plums).
• Describe Bohrs nuclear model and how it came about.

  The nuclear model suggests electrons orbit the nucleus at specific distances (shells) - it came about from the alpha scattering experiments.
• Later experiments led to the discovery of smaller, positive particles in the nucleus. What are these particles called?


  Protons.
• What did the work of James Chadwick provide evidence for?


  The existence of the neutron In the nucleus.
• Describe the structure of an atom.


  The atom has a small central nucleus (made of protons and neutrons) with electrons orbiting it in shells.
• State the relative mass of a proton.

  1
• State the relative mass of a neutron.

  1
• State the relative mass of an electron.


  Very small.
• State the relative charge of a proton.


  +1
• State the relative charge of a neutron.


  0
• State the relative charge of an electron.


  -1
• Explain why atoms are electrically neutral.

  The electrons and protons are the same so the relative charges cancel each other out.
• What’s the radius of an atom?


  0.1 nm.
• What’s the radius of a nucleus and what fraction of the atom is it?


  The radius is 1x10^-14 m which is 1/10000 of the atom.
• What is the same given to the number of protons in the nucleus?

  Atomic number.
• Atoms of the same element have the same number of which particle in the nucleus?


  Protons.
• Where’s is the majority mass of an atom?


  The nucleus.
• Define mass number.


  The total number of protons and neutrons.
• Using the mass and atomic number what is the calculation to find the number of neutrons?


  Subtract atomic number from mass number.
• What is an isotope?

  Atoms of the same element (same proton number) with a different number of neutrons.
• Do isotopes of a certain element have the same chemical properties?

  Yes because their electron structure is the same.
• What’s the relative atomic mass?

  The average mass value which takes the mass and abundances of the isotopes of that element into account.
• How many electrons does the first then second shell hold?

  First shell: 2 electrons Second shell: 8 electrons