Chapter 2 - Atomic structure and isotopes

Question 1

What is the mass number ?

Answer 1

• The bigger number

- Protons and neutrons

Question 2

What is the atomic number ?

Answer 2

• The smaller number
• Number of protons
• P=E, unless its charged

Question 3

How do you find out the number of neutrons ?

Answer 3

Mass number - atomic number

Question 4

What are isotopes ?

Answer 4

Isotopes are atoms of the same element with different numbers of neutrons and therefore different masses. e.g. 35-Cl and 37-Cl

Question 5

What do isotopes with more neutrons have ?

Answer 5

• Higher mass
• Higher density
• Higher MP + BP
• Slower rates of diffusion

Question 6

What are ions ?

Answer 6

An ion is a charged atom. It has gained or lost electrons meaning the number of electrons is different from the number of protons

Question 7

What are cations ?

Answer 7

Cations are positive ions with a positive charge. They have lost electrons. Commonly found on the LHS of the periodic table.

Question 8

What are anions ?

Answer 8

Anions are negative ions with a negative charge. They have gained electrons. Commonly found on the RHS of the periodic table.

Question 9

What is relative atomic mass ?

Answer 9

Relative atomic mass is the weighted mean mass of an atom relative to 1/12th the mass of an atom of carbon-12

Question 10

What is relative isotopic mass ?

Answer 10

Relative isotopic mass is the mass of an isotope relative to 1/12th the mass of an atom of carbon-12

Question 11

What is relative formula mass ?

Answer 11

Relative formula mass is the mass of its formula units relative to carbon-12

Question 12

How does a mass spec work ?

Answer 12

• A sample is placed in the mass spec
• The sample is ionised. It is bombarded with electrons which knock off electrons, forming positive ions
• The ions are then accelerated. Heavier ions move more slowly and are more difficult to deflect, whereas lighter ions move quicker and are easier to deflect
• The ions are then detected on a mass spectrum as a mass to charge ratio (m/z). Each ion reaching the detector adds to the signal, so the greater the abundance, the larger the signal.

Question 13

What does the furthest right peak represent ?

Answer 13

The peak furthest to the right is known as the molecular + ion. It has the highest mass and is therefore the parent molecule.

Question 14

How to calculate relative atomic mass using a mass spec ?

Answer 14

∑ ( percentage abundance of each isotope × mass of each isotope ) ÷ 100

Question 15

What are binary compounds ?

Answer 15

A binary compound contains two elements only

Question 16

What are polyatomic ions ?

Answer 16

When an ion contains atoms of more than one element bonded together

Question 17

Key polyatomic ions

Answer 17

• Ammonium ion - NH4 (+)
• Hydroxide ion - OH (-)
• Nitrate ion - NO3(-)
• Nitrite ion - NO2(-)
• Hydrogencarbonate ion - HCO3(-)
• Manganate(VII) ion - MnO4(-)
• Carbonate ion - CO3(2-)
• Sulphate ion - SO4 (2-)
• Sulphite ion - SO3(2-)
• Dichromate(VI) - Cr2O7(2-)
• Phosphate ion - PO4(3-)
• Zinc ion - Zn(2+)
• Sodium ion - Na(+)
• Halide ion - F,Cl,Br,I,At(-)
• Aluminium ion - Al3(+)

Question 18

Charges in different groups in the periodic table

Answer 18

• Group 1 = 1+ charge
• Group 2 = 2+ charge
• Group 3 = 3+ charge
• Group 5 = 3- charge
• Group 6 = 2- charge
• Group 7 = 1- charge