S1.2 The nuclear atom

Question 1

what do atoms contain?

Answer 1

• a positively charged, dense nucleus composed of protons and neutrons (nucleons)
• negatively charged electrons occupy the space outside of the nucleus, they orbit the nucleus and create a ‘cloud’ of negative charge

Question 2

mass number

Answer 2

protons + neutrons

Question 3

atomic number

Answer 3

protons (= number of electrons)

Question 4

proton relative mass and charge

Answer 4

RM = 1
RC = +1

Question 5

neutron relative mass and charge

Answer 5

RM =1
RC = 0

Question 6

electron relative mass and charge

Answer 6

RM = 1/1836
RC = -1

Question 7

why are relative masses of subatomic particles used?

Answer 7

the values are so small

Question 8

isotope of an element

Answer 8

• has the same number of protons but a different number of neutrons
• same chemical properties
• slightly different physical properties
• mass numbers are different

Question 9

relative atomic mass of an element

Answer 9

the weighted average of the masses of the isotopes relative to 1/12 of the mass of a C-12 atom

Question 10

Ar formula

Answer 10

Ar =∑(% abundance x mass)/100

Question 11

what can be used to find the percentage abundance of isotopes

Answer 11

a mass spectrometer

Question 12

process of finding the percentage abundance of isotopes using a mass spectrometer

Answer 12

• vapourise
• ionise to form positive ions
• accelerate ions
• each ion produces a signal which is detected as a mass-to-charge ratio (m/e)
• use this to calculate Ar