Chemistry Atomic Structure

Atomic Mass

One twelfth the mass of a single carbon - 12 atom

Atomic Number

Number of protons in the nucleus

Mass number

The number of protons plus neutrons

Positive ions are called

Cations

Negative ions are called

Anions

What identifies a particular atom?

It’s specific/unique proton/atomic number

Isotopes have what?

Same proton number but different mass number

What are the steps of electro spray ionisation?

1. Dissolved in a volatile solvent

2. A high voltage is applied

3. The high voltage removes a proton from the solvent, and attaches it to the sample molecule.

4. The sample molecules are now positively charged ions.

5. Molecules are accelerated to have the same kinetic energy

6. They hit a negatively charged plate

7. Creating a current proportional to the number of ions produced

8. Telling us the abundance of the molecule

What is electro spray ionisation typically used for?

Polymers and biological materials

What are the steps of electron impact ionisation?

1. The sample is vaporised

2. Hit with electrons from an electron gun

3. Which knock other electrons off from the molecule, creating positively charged ions

4. But often causes the sample to fragment

1. Molecules are accelerated to have the same kinetic energy

2. They hit a negatively charged plate

3. Creating a current proportional to the number of ions produced

4. Telling us the abundance of the molecule

Why do we look at the peak with the highest m/z ratio?

Because that is the molecular ion peak representing the mass/charge value of the molecules we are analysing

What do clustered small peaks around the molecular ion peak represent?

Isotopic molecules

What is relative atomic mass?

A value taking into account all of an atoms isotopes and their relative abundances, this is what you calculate

Define relative isotopic mass

Average mass of an isotope compared to mass of 1/12th of a carbon - 12 atom

Why does C2H2 have a higher boiling point than CH4?

Ethane is a larger molecules so it has more electrons

There are stronger Van der Waals forces between ethane molecules

How can we identify transition metals from their electron configuration?

They have a partially filled D subshell.