2.1.1 Atomic structure and isotopes

Question 1

describe the current model of the atom

Answer 1

• protons + neutrons found in nucleus
• electrons orbit nucleus in shells
• nucleus is small and dense and accounts for almost all of atoms mass
• most of atom consists of empty space with positive nucleus region in centre surrounded electron shells

Question 2

what are the relative mass of p, n, e

Answer 2

p - 1
n - 1
e - 1/1836

Question 3

what are the relative charges of p, n, e

Answer 3

p - +1
n - 0
e - -1

Question 4

what is the atomic number

Answer 4

number of protons

Question 5

what is the mass number

Answer 5

• number of protons + neutrons

Question 6

atoms of the same element have the same …

Answer 6

• number of protons

Question 7

what identifies an element

Answer 7

• the number of protons

Question 8

what are isotopes

Answer 8

• atoms of the same element with different number of neutrons but same protons
  > and so different masses

Question 9

why do we use relative mass + charge to describe subatomic particles

Answer 9

• because the actual mass + charge is very small number

Question 10

do isotopes of an element react differently

Answer 10

• chemical reactions involve the electrons
• isotopes have same number of electrons and therefore they react in the same way
  > there may be some small differences in physical properties e.g. mp / bp

Question 11

what is an ion

Answer 11

• a charged atom
• number of electrons is different than protons

Question 12

what is the carbon-12

Answer 12

• the international standard for the measurement of atomic mass

Question 13

what is relative isotopic mass

Answer 13

• the mass of an isotope relative to 1/12th the mass of an atom of carbon-12

Question 14

what is relative atomic mass, Ar

Answer 14

• the weighted mean mass of an atom of an element relative to 1/12th the mass of an atom of carbon-12

Question 15

what is relative formula mass

Answer 15

• used for giant structures
• the weighted mean mass of a formula unit compared with 1/12th the mass of an atom of carbon-12

Question 16

what is relative molecular mass

Answer 16

• used for simple molecules
• the weighted mean mass of a molecule compared with 1/12th the mass of an atom of carbon-12

Question 17

how do you find the relative atomic mass of the following:
123 atoms of B
23 are B-10
100 are B-11

Answer 17

Ar = (23 x 10) + (100 x 11)
= ans / 123 = 10.8

Question 18

what is a mass spectrometer used for

Answer 18

• it finds out about molecules e.g.
  > identify an unknown compound
  > find relative abundance of each isotope of an element
  > determine structural information about molecules

Question 19

how does a mass spectrometer determine the mass of a molecule or isotope

Answer 19

• by measuring the mass-to-charge ratio of ions
  > m/z = relative mass of ion / relative charge of ion
• sample placed in mass spectrometer
• sample vaporised and ionised to form +1 ions
• ions accelerate, heavier ions move slower than lighter ones
• ions detected and current produced to form a mass spectrum