Atomic structure and the Periodic table

• What do Atoms contain?

  • Protons
  • Neutrons
  • Electrons
• What is the approximate radius of an atom?

  0.1 nanomenters (1 x 10^-10m)
• What is the nucleus?

  • It's in the middle of the atom
  • It contains protons and neutrons
  • It has a positive charge because of the protons
  • Almost the whole mass of the atom is concentrated in the nucleus
• The Electron

  • Move around the nucleus in electron shells
  • They're negativeley charged and tiny, but they cover a lot of space
  • The volume of their orbits determines the size of the atom
  • They have virtually no mass
• Number of Protons Equals Number of Electrons

  • Atoms are neutral - they have no charge overall (unlike ions)
  • This is because they have the same number of protons neutrons and electrons
  • The charge on the electrons is the same charge on the protons, but opposite - so the charges cancel out
  • In an ion the number of protons doesn't equal the number of electrons. This means it has an overall charge. Example: an ion with a -2 charge, has two more electrons than protons
• Atomic Number and Mass Number Describe and Atom

  • The number symbol of an atom tells you its atomic (proton) number and mass number
  • The atomic number tells you how many protons there are
  • The mass number tells you the total number of protons and neutrons in the atom
  • To get the number of neutrons, you have to subtract the atomic number and the mass number
• Isotopes

  • Isotopes are different forms of the same element which have the same number of protons but a different number of neutrons
  • So isotopes have the same atomic number but a different mass number
• Relative atomic mass

  • Because many element cam exist as a number of differen isotopes, relative atomic mass (Ar) is used instead of mass number when refferring to the element as a whole.
• Relative atomic mass

  • Because many element can exist as a number of differen isotopes, relative atomic mass (Ar) is used instead of mass number when refferring to the element as a whole.
  • This is an average taking into account the different masses and abundances (amounts) of all the isotopes taht make up the element
  • The formula to work out the relative atomic mass:

  sum of (isotope abundance x isotope mass number)/ sum of abundances of all the isoptopes
• Compounds

  • Compounds are substances formed from two or more elements, the atoms of each are in fixed proportions throught he compound and they're held together by chemical bonds
  • Because the chemical bond is very strong it quite dificult to separate the original elements of a compound out again - a chemical reaction is needed to do this
• Making compound bonds:

  • Making bonds involves atoms giving away, taking or sharing electrons. Only the electrons are involved - the nuclei of the atoms aren't affected at all when a bond is made
• Metal and non-metal compound:

  • The metal atoms lose electrons to form positive ions
  • The non-metals atoms gain electrons to form negative ions
  • The opposite charges (positive and negative) of the ions mean that they're strongly attracted to each other.
  • This is called ionic bonding
• Non-metal compounds:

  • Each atom shares an electron with another atom
  • This is called covalent bonding
• Mixtures

  • There is no chemical bond between the different pars of a mixture
  • The parts of a miture can be iethe elements of compounds
  • Mixtures can be separtated out by physical methods such as:

  Filtration

  Crytallistation

  Simple distillation

  Fractional distillation

  Chromotography
• Filtration

  • Filtration can be used if your product is an insoluble solid that needs to be separated from a liquid reaction mixture
  • It can be used in purification as well. Example: solid impurities in the reaction mixture can be sparated out using filtration
• What are the two ways to separate Soluble Solids from Solutions?

  • Evaportation
  • Cystallisation
• Evaportation is a really quick way of speparting a soluble salt from a solution, but you can only use it if the salt dosn't decompose (break down) when it's heated.

  Otherwise you will have to use Crystallisation.
• The method of how to do evaportation:

  1. Pour the solution into an evaporating dish
  2. Slowly heat the solution. The solvent will evaporate and the solution will get more concentrated. Eventually, crystals will start to form
  3. Keep heating the evaporting dish untill all you have left are dry crystals
• The method of how to do Crystallistation

  1. Pour the solution into a evaporating dish and gently heat the solution. Some of the solvet will evaporate and te solution will get more concentrated
  2. One some of the solvent has evaportated, or when you see crtals start to form, remove the dish from the heat and lave the solutio to cool
  3. The salt should start to form crystals as it becomes insoluble in the cold, higly concentrated solution
  4. Filter the crystals out of the solution, leave then in a warm place to dry.
• What is Simple Distillation is used for

  Simple distillation is used for separating out a liquid from a solution
• How does Simple Distillation work?

  • The solution is heated. The part of the solution that has the lowest boiling point evaportates first.
  • The vapour is then colled condenses (turns back into a liquid) and is collected
  • The rest of the solution is left behind in the flask
• What is the problem with simple distillation?

  The problem with simple distillation is that you can only use it to separate things with very different boiling points - if the temperateure goes higher than the boiling point, they will mix again

  If you have a mixture of liquids with similar boiling points you need anither method to separate then - like fractional distillation
• What is fracion distillation used for?

  If you have a mixture of liquid you can separate it useing fractional distillation
• Fill in the gaps

  A) John Dalton

  B) Solid sphere model

  C) J.J Thompson

  D) Plum pudding model

  E) E. Rutherford

  F) Nuclear model

  G) Bohr

  H) Planetary model

  
• John Dalton and the solid sphere model

  John Dalton described atoms as solid spheres and that different spheres made different elements
• J J Thompson and the Plum pudding model

  J J Thompson discorved from his experiments that atoms must contain even smaller, negatively charged particles - electrons.

  The structure of the Plum pudding model shows a ball of positive charge with electrons embeded in.
• What was the famous experiment that proved the plum pudding model was wrong?

  Rutherford's alpha particle scattering experiment
• What was expected to happen from the alpha particle scattering experiment?

  From the plum pudding model, they were expecting the particles to pass straight through the sheet of gold foil or be slightly deflected.
• Why did they expect the alpha particles to go straight through the gold foil?

  This was because the positive charge of each atom was thought to be very spread out through the 'pudding' of the atom.
• What actually happened in the alpha particle scattering experiment?

  Most of the particles did go straight through the gold sheet, some were deflected more then expected, and a small number were defelcted backwards.

  This meant that the plum pudding model couldn't be right.
• What did Rutherford do with his findings of the alpha particle scattering experiment?

  He made the nuclear model.

  In this, there's a tiny, positively charged nucleus at the centre, most of the mass is concentrated.

  A 'cloud' of negative electrons surroundin the nucleus - so that most of the atom is an empty space.
• What did Bohr discover that was wrong about Rutherford's nuclear model?

  That the electrons in a 'cloud' around the nucleus of the atom would be attracted to the nucleus causing it to collapse.
• What did bohr think happened to electrons in the atom?

  Bohr proposed that electrons orbit the nucleus in fixed shells and aren't anywhere in between. Each shell is a fixed distance from the nucleus.
• What did James Chadwick discover?


  The neutron.
• Why did it take so long to discover the neutron?

  Neutrons have no charge and are neutral, making them difficult to detect.
• Who is the 'Father' of the periodic table?

  Dmitri Mendeleev
• Why was Mendeleev so important in his development in the periodic table?

  He left out gaps for undiscovered elements and predicted there properties. When these missing elements were discovered they had the same properties that Mendeleev predicted and they fit in the gap in his periodic table.
• Hoe is the modern periodic table arranged in?

  They are arranged in the order of atomic number
• What are ions?


  Different number of protons or electrons. They are either positively charged or negatively charged.
• What is the reactivity going down group 1?

  Increases