Atomic Structure - Physical 1

Question 1

Which letter is used to represent the atomic number of an atom?

Answer 1

Z

Question 2

What does the atomic number tell us about an element?

Answer 2

Atomic number = number of protons in an atom

Question 3

What letter represents mass number?

Answer 3

A

Question 4

How is the mass number calculated?

Answer 4

mass number = number of protons + number of neutrons (total number of nucleons)

Question 5

Define relative atomic mass

Answer 5

Average mass of all isotopes of an element compared to 1/12 the mass of an atom of Carbon 12 (C12)

Question 6

What is are isotopes of an element?

Answer 6

Different forms of the same element, containing the same number of protons but different numbers of neutrons. They still have the same chemical properties

Question 7

What is the full electron configuration for the different s=orbital?

Answer 7

1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6

Question 8

How do you work out number of orbitals?

Answer 8

For each energy level the max number of electrons can be determined using the formula, 2n^2.
Where n is the energy level

Question 9

Does 3d or 4s have a higher energy?

Answer 9

3d

Question 10

What is an orbital?

Answer 10

A region around the nucleus that can hold up to two electrons

Question 11

What would be the relationship between 2 electrons in the same orbital in terms of their spin?

Answer 11

Have opposite spin as repel each other as both negative

Question 12

Explain why chromium does not fit the trend for electronic configuration

Answer 12

It only has one electron in its 4s orbital before filling 3d
1s2 … 3p6 4s1 3d5

Question 13

Explain why copper does not for the trend for electronic configuration.

Answer 13

It only has one electron in its 4s orbital before filling 3d
1s2 … 3p6 4s1 3d10

Question 14

What are the two types of ionisation for a mass spectrometer? How do they differ?

Answer 14

1. Electron impact: electron gun (hot wire filament with current through it emitting electrons) knocks off one electron from each particle to form 1+ MOLECULAR IONS (these ions fragment).
2. Electrospray: sample dissolved in volatile solvent (e.g. water or methanol) and injected through a fine hypodermic needle to give an aerosol. Needle attached to positive terminal of a high-voltage power supply and particles gain a proton from the solvent as they leave the needle, producing XH+ ions (+1 charge and mass of Mr + 1). (ions rarely fragment)

Question 15

When would you use the different types of ionisation in a mass spec?

Answer 15

Electron impact used for organic or inorganic molecules with a low formula mass.
Electrospray used for substances with a higher molecular mass including biological molecules, e.g. proteins.

Question 16

Describe how a time of flight mass spectrometer works

Answer 16

Acceleration - positive ions attracted towards a negatively charged plate.
Ion Drift - ions pass through hole in plate, form a beam with constant kinetic energy, travel along tube to detector. Time of flight is therefore directly proportional to the square root of mass.
Detection - positive ions pick up electrons, current flows, m/z value and time of flight recorded. Largest current from most abundant ions

Question 17

Define first ionisation energy

Answer 17

The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions

Question 18

does the 4s or 3d sub shell fill first and why?

Answer 18

the 4s fills before the 3d orbital due to the 4s orbital having a lower energy level than the 3d orbital

Question 19

time of flight formula

Answer 19

t=d. (square root of all next bit) m/2ke

remember s - d/t

get mass do x / 1000