S1.2 - the nuclear model

Question 1

What does an atom contain?

Answer 1

Protons and neutrons (in the nucleus) and electrons (in shells).

Question 2

What is the mass number?

Answer 2

Mass number - number of protons + number of neutrons.
- Also called the nucleon number.
- Top number of an element.

Question 3

What is the atomic number?

Answer 3

Atomic number - number of protons = number of electrons.
- Bottom number in an element.

Question 4

What are ions?

Answer 4

Atoms that have lost or gained electrons.

Question 5

What are cations and anions?

Answer 5

Cations - positive ions
Anions - negative ions

Question 6

What is RAM?

Answer 6

RAM - average mass of all isotopes relative to an atom of Carbon-12.

Question 7

What is a plasma?

Answer 7

Plasma - an atom that has been stripped off of it’s electrons so is a positive ion with loosely attracted electrons that only exist at high temperatures and pressures.

Question 8

What is an isotope?

Answer 8

Isotope - an element that contains the same number of protons and electrons, but a different amount of neutrons.

Question 9

What are some uses of isotopes?

Answer 9

• Carbon dating
• Nuclear energy in power stations
• Tracing pollution levels
• PET scans and tracers

Question 10

How do you work out abundance of an isotope?

Answer 10

(% abundance of isotope x Mr of isotope) / 100

Question 11

Why is mass spectra used?

Answer 11

Determines the relative atomic masses of elements from their isotopic composition to form a mass spectrum

Question 12

How is mass spectra carried out?

Answer 12

1) Element is vaporized to analyze the individual atoms.
2) Element is ionized by high energy electrons to knock off electrons and produce a positive ion.
X(g) + e- –> X+(g) + 2e-
3) Positive ions are attracted to the negative plate and deflected by a magnetic field at right angles.

Question 13

How is mass spectra interpreted?

Answer 13

Deflection is inversely proportional to mass/charge value

Question 14

How can you use mass spectra to identify the molecular mass of the substance you are investigating?

Answer 14

Look at the parent ion peak, which is the peak furthest to the right in the mass spectrum.

Question 15

What is fragmentation?

Answer 15

Collisions during the ionization stage are so energetic between the electron and the molecules fragment, which can be used to identify the structure of a compound

Question 16

What is a parent ion peak?

Answer 16

Molecular ion peak - corresponds to the ion formed when a molecule loses or gains electrons without any fragmentation.