C1.2 (atomic structure)

• describe the role of an atom in an element?

  An atom is the smallest particle of an element that still has its chemical properties, different elements are made from different atoms
• what is a molecule?


  It is made from 2 or more atoms joined together, they are joined by attractive forces called chemical bonds
• what is an oxygen molecule made from?

  2 oxygen atoms
• what is a carbon dioxide molecule made from?

  1 carbon atom and 2 oxygen atoms
• what is the difference between elements and molecules?


  Elements are a pure substance where all of the atoms are the same such as gold, whereas molecules can be made of many different atoms such as carbon dioxide
• define atomic radius


  half of an atom's diameter
• define bond length?


  The distance between the centres of 2 joined atoms
• how can you link atomic radius and bond length when the atoms are the same?


  Atomic radius is half of the bond length, normally around 10^-10 m
• what are the 3 subatomic particles and what are their charges?


  The 3 subatomic particles are protons, neutrons, and electrons. Protons have a positive charge, neutrons have no charge, and electrons have a negative charge.
• where are the subatomic particles found?

  Protons and neutrons are joined together as the nucleus at the centre and electrons are in shells surrounding the nucleus
• what is the radius of the nucleus compared to the radius of the atom?

  100,000 times smaller
• what is the relative charge and relative mass of a proton?


  Relative charge: +1

  Relative mass: 1
• what is the relative charge and relative mass of a neutron?

  Relative charge: 0

  Relative mass: 1
• what is the relative charge and relative mass of an electron?


  Relative charge: -1

  Relative mass: 0.0005
• what does the term relative refer to when talking about atoms?


  It helps make very small numbers easier to understand and to be able to see the difference between them. eg. a proton's relative mass is 1 and an electron's relative mass is 0.0005 which shows just how tiny an electron is
• what does a full chemical symbol for an atom give you?

  Its chemical symbol and 2 numbers
• what is the bottom number in a chemical symbol?


  The number of protons in its nucleus and how many electrons are present
• what is the top number in a chemical symbol?


  The element's mass number (total number of protons and neutrons)
• what is the equation for the mass number?


  Mass number = number of protons (atomic / bottom number) + number of neutrons
• how do you work out the number of neutrons?


  Mass number (total of protons and neutrons) - atomic number (total number of protons)
• what are isotopes of an element?

  atoms with the same number of protons and electrons but with different numbers of neutrons
• what do isotopes have in common with the element?


  They have the same atomic number but their mass number is different
• what do chemical properties of an element depend on?

  The number of electrons in its atoms
• what is similar between all the isotopes of an element?

  They have the same number of electrons, so they have identical chemical properties
• what is different between all the isotopes of an element?


  The different number of neutrons may may affect their physical properties
• what are ions?


  Charged particles
• when are ions formed?


  When atoms (or groups of atoms) lose or gain electrons, often during chemical reactions
• what happens in the reaction between sodium and oxygen?


  A sodium atom loses one electron to become a sodium ion (NA+)

  An oxygen atom gains two electrons to become an oxide ion (O2-)
• what did John Dalton do in 1803?


  suggested that all matter is made from atoms, and provided a detailed model
• what did Dalton's model explain?

  all atoms of an element are identical

  different elements contain different types of atom
• what did JJ Thomson do?


  He discovered the first subatomic particle (the electron) in 1897
• how did Thomson discover this?


  In his experiments, he found that 'cathode rays' changed directions in electric and magnetic fields, he concluded that cathode rays were actually tiny negatively charged particles that were much smaller than atoms
• what 2 observations did Thomson's model have to make sense of?


  -atoms contain electrons

  -atoms are neutral overall
• what model did Thomson make?

  The plum pudding model, he suggested that atoms are spheres of positive charge with electrons dotted around inside them like pieces of fruit in a cake
• what did Ernst Rutherford test and with who?

  He tested the plum pudding model alongside Hans Geiger and Ernest Marsden
• how did Rutherford test the plum pudding model?

  In 1909, they pointed beams of positively charged particles (alpha particles) at thin gold foil
• what were the results of this experiment?

  most of the particles went straight through, many of them changed direction slightly and some even came straight back
• how did Rutherford explain the results of the gold foil experiment?


  He suggested that an atom has a positively charged nucleus containing most of its mass, he also suggested that outside the nucleus, electrons orbit like planets in a solar system
• What did Niels Bohr do?


  He realised that orbiting electrons would be attracted to the oppositely charged nucleus and would spiral inwards, in 1913 he made improvements to Rutherford's model and showed that electrons occupy fixed energy levels (shells) around the nucleus
• How did Bohr make improvements to Rutherford's model?

  Using mathematical models