U1.2: The Nuclear Atom

Question 1

Define atomic number

Answer 1

The number of protons in the nucleus of an aotm

Question 2

Define atomic mass number

Answer 2

The number of protons + neutrons in an atom

Question 3

Define relative atomic mass

Answer 3

the average mass of all the isotopes of an element relative to 1/12th of the mass of Carbon-12 atom

Question 4

Define atomic mass units (AMU)

Answer 4

Used to express the masses of atomic particles

Question 5

Formula for relative atomic mass

Answer 5

[Isotope 1(%1) + Isotope 2(%2) +…. ] / 100

Question 6

Formula for relative abundance

Answer 6

one of the isotopes is x, the other is 100-x

• Atomic mass of isotope1(x) + atomic mass of isotope2(100-x) ALL DIVIDED BY 100 = Mr of element
• solve for x (which is the abundance of one of the isotopes) then find 100-x (which is the abundance of the other isotope)

Question 7

Define isotopes

Answer 7

Isotopes contain the same number of protons but a different number of neutrons of the same element

Question 8

What properties of isotopes are different

Answer 8

The physical properties:
- Density
- Rate of diffusion
- Boiling point

Question 9

What is the trend of isotopes?

Answer 9

Similar chemical properties, different physical properties although they all react the same way

Question 10

What is the mass spectrometer

Answer 10

It’s used to determine the relative atomic mass of gaseous elements and can also show isotopic composition

Question 11

What elements go through the mass spectrometer faster?

Answer 11

Lighter elements

Question 12

How to find mass lost on fragmentation pattern

Answer 12

Furthest peak subtracted with the next peak to obtain a value of which is the mass lost. That shows the fragment lost

Question 13

What do the peaks show on the fragmentation pattern

Answer 13

Peaks show the relative abundances of the number of isotopes present

Question 14

What does the height of each peak indicate

Answer 14

The relative abundance of the respective isotope

Question 15

How to find relative molecular mass when given a mass spectrum?

Answer 15

Look for molecular ion peak to find abundance and read m/z ratio to find Mr
- use formula: m1(%abundance) +… /100

Question 16

Compare the chemical properties of all isotopes and justify your reasoning

Answer 16

Chemical properties of all isotopes are similar because they have the same number of electrons; It’s the electrons that are responsible for chemical properties

Question 17

Why would the RAM of one element be greater than the RAM of another’s even if the Ar of the second element’s greater than the Ar of the first?

Answer 17

The RAM would be greater due to greater number of neutrons in one element compared to the other

Question 18

Does the chloride ion or chlorine atom have a larger radius? Justify your reasoning

Answer 18

Cl ion has a larger radius due to more electron-electron repulsion

Question 19

In terms of isotopes. what does 1:1 ratio mean

Answer 19

The average of the 2 mass numbers given

Question 20

What is affected when an element has an isotope of fewer neutrons in its atom

Answer 20

The isotope has a lower density

Question 21

Define relative abundance

Answer 21

Relative abundance is the percent abundance in nature of a particular isotope

Question 22

How to find relative molecular mass of an element using mass spectrum

Answer 22

• Determine if it is a diatomic molecule or not; if yes, multiply Mr by 2 and only look at peaks on or past that point
• m/z(relative intensity) + 2nd m/z(2nd relative intensity) +… ALL DIVIDED BY RELATIVE INTENSITIES MULTIPLIED WITH ADDED UP

Question 23

in a mass spectrum of chlorine gas, what particle causes the peak at 35 m/z. Also, why does it have the charge it has

Answer 23

Cl-35 +
- This has a positive charge as the peak is from a single atom of Cl-35 that has been bombarded with electrons in the mass spectrometer resulting in the positively charged particle