Chapter 2- Atoms, ions and compounds

• What was stated in Daltons's atomic theory? (4 points)

  - Atoms are tiny particles that make up elements.

  - Atoms cannot be divided.

  - All the atoms in an element are the same.

  - Atoms of one element are different to those of other elements.
• What did Thompson discover about electrons? (3 points)

  - They have a negative charge.

  - they can deflected by magnets and electric fields.

  - They have a very small mass.
• Explain the plum pudding model.


  Atoms are made up of negative electrons mocing around in a sea of positive charge.
• What were Rutherford's proposals after the gold leaf experiment? (4 points)

  - Most of the mass and positive charge of the atom are in the nucleus.

  - Electrons orbit the nucleus.

  - Most of the atom's volume is the space between the nucleus and electrons.

  - Overall positive and negative charges must balance.
• Explain the current model of the atom (5 points)

  - The nucleus is made up of protons and electrons.

  - Most of the atom's mass is in the nucleus.

  - Electrons orbit in shell (aka energy levels)

  - The nucleus is 1/1836 the relative mass. It therefore has a tiny volume compared to the atom.

  - Most of the atom is empty space.
• How many elements are on the periodic table?

  118
• True or False: Atoms from the same element contain the same number of protons.

  True.
• What is the relative charge and mass of a:

  - proton

  - electron

  - neutron

  
• Which subatomic particle has the same mass as a proton?

  Neutrons - they make up most of an atom's mass.
• What is the role of neutrons?

  They are subatomic particle that holds the nucleus together despite the electrostatic forces of repulsion between the protons.
• What letter is used to represent the atomic number of an atom? What does it tell you about the element?

  Z.It tells you the number of protons in an atom. It technically also tells you the number of electrons in an atom asnumber of protons + number of electrons = 0.
• Which letter represents the mass number? What does it tell you about the atoms?

  A. It tells you the number of neutrons using the formula:

  Number of neutrons = mass number - number of protons (atomic number)
• What is the definition of an isotope?

  Atoms of the same element with a different number of neutrons.
• Why do different isotopes of the same element react in the same way (even though they have different mass numbers)?

  Neutrons have no impact on the chemical reactivity. Reactions involve electrons isotopes have the same number of electrons in the same arrangement.

  
  

  This however causes slight differences in physical properties.
• What are ions? What is the charge when an atom gains and when it loses electrons?

  Charged particles that are formed when an atom loses or gains electrons.

  
  

  When it gains electrons it has a negative charge but when it loses electrons it has a positive charge.
• What is the unit used to measure atomic masses called? What is the mass of a carbon-12 isotope?

  Unified atomic mass unit,u

  The mass of a carbon-12 isotope is12u.
• What is the definition of relative atomic mass? Does it have units? If so what are they?

  The weighted mean mass of an atom of an element compared with 1/12 of the mass of an atom of carbon-12.

  It does not have any units.
• What is there formula for the mass-to-charge ratio for ions in a mass spectrometer?


  Relative mass of ion

  Mass-to-charge ratio = ———————————————

  Relative charge on ion
• What is the definition of relative isotopic mass? What number is this the same as?

  The mass of an atom of an isotope compared with 1/12 of the mass of an atom of carbon-12.

  It is the same as the mass number.
• What are the 2 assumptions made when calculating the mass number?

  - The contribution of the electron is neglible.

  - The mass of the proton and neutron is 1.0 u
• How do you calculate the relative molecular and formula mass?


  They can be calculated by adding the relative atomic masses of each atom making up the molecule.
• What are the uses of mass spectrometry? (3 points)

  - Identify unkown compounds.

  - Find relative abundance of isotopes in an element.

  - Determine structural information.
• How does a mass spectrometer work? (3 points)


  - The sample is made into positive ions.

  - They pass through the apparatus and are separated according to mass to charge ratio.

  - A computer analyses the data and produces a mass spectrum.
• How is the group number related to the number of valance shell electrons?

  The group number (1 to 8) state the number of valance shell electrons on that atom (eg- Na (group 1) has 1 valance shell electron and oxygen (group 6) has 6 valance shell electrons).
• Are groups or periods vertical?

  Groups are vertical.

  Periods and horizontal.
• Is it metals or non- metals that usually lose electrons?

  Metals.

  
  

  Non metals tend to gain electrons.
• Which are the 4 elements that don't tend to form ions and why?

  - Beryllium (Be)

  - Boron (B)

  - Carbon (C)

  - Silicon (Si)

  
  

  This is due to thhe fact that they require aa lot of energy to transfer outer shell electrons.
• What are molecular ions?

  Covalently bonded atoms that lose or gain electrons.