2.1-3- Atomic structure and isotopes/Relative mass/Formulae and equations

Question 1

What are the charges/relative masses of the 3 subatomic particles?

Answer 1

• proton (p+) – 1+ – 1
• neutron (n) – 0 – 1
• electron (e-) – 1- – 1/1836

Question 2

What does the periodic table show?

Answer 2

• lists elements in order of the number of protons in the nucleus (atomic number)

Question 3

What is an isotope?

Answer 3

• an atom of the same element with different numbers of neutrons and different masses

Question 4

How do isotopes affect chemical reactions?

Answer 4

• chemical reactions involve electrons around the nucleus
• isotopes of the same element have the same number of electrons
• so different isotopes of an element will react the same as the neutrons do not affect the chemical reactions that take place

Question 5

Properties of isotopes with more neutrons:

Answer 5

• higher mass
• higher density
• higher melting/boiling points
• slower rates of diffusion

Question 6

What is an ion (+/-)?

Answer 6

• it is a charged atom
• cations are positive ions (fewer electrons)
• anions are negative ions (more electrons)

Question 7

What is the standard isotope used to base all atomic masses?

Answer 7

• carbon-12

Question 8

What is relative isotopic mass?

Answer 8

• the mass of an isotope relative to 1/12th of the mass of the mass of an atom of carbon-12
• no units as it is the ratio of 2 masses

Question 9

What is relative atomic mass?

Answer 9

• the weighted mean mass of an atom of an element relative to 1/12th of the mass of an atom of carbon-12
• it takes into account:
  • the % abundance of each isotope
  • the relative isotopic mass of each isotope

Question 10

What do ‘Z’ and ‘Ar’ mean?

Answer 10

• Z = atomic number
• Ar = relative atomic mass

Question 11

What does a mass spectrometer do?

Answer 11

• helps to experimentally find the % abundances
• it determines the relative isotopic mass and relative abundances of an isotope

Question 12

How does a mass spectrometer work?

Answer 12

• sample is placed inside the MS
• it is vaporised and bombarded with electrons to knock out one electron from the sample to form a positive ion
• these ions are then accelerated (heavier ones move slower/are harder to deflect) which separates them
• the MS measures the mass:charge ratio (m/z = mass/charge)

Question 13

Mass Spectrum graph

Answer 13

• x-axis : m/z
• y-axis : relative abundance
• final peak : molecular ion peak (relative molecular mass)
• base peak : most common/abundant ion

Question 14

Simple ions from the periodic table (cations/anions)

Answer 14

• metals on the left form cations (+ve)
• non-metals on the right form anions (-ve)

Question 15

What is a binary compound?

Answer 15

• it is a substance that contains two elements only
• ‘first element’ + ‘second element with -ide ending’
• ionic compounds : metal ion always comes first

Question 16

What is a polyatomic ion (+ examples)?

Answer 16

-an ion that contains more than one element
- examples :
- NH^+ (ammonium)

 - OH^- (hydroxide)
 - NO3^- (nitrate)
 - NO2^- (nitrite)
 - HCO3^- (hydrogencarbonate)
 - MnO4^- (manganate (VII))
 
 - CO3^2- (carbonate)
 - SO4^2- (sulfate)
 - SO3^2- (sulfite)
 - CrO7^2- (dichromate (VI))

 - PO4^3- (phosphate)