CHEMISTRY ATOMIC STRUCTURE (PHYSICAL)

Chemistry- y12

What was Dalton’s model?

An indivisible solid sphere.

What was Thompson’s model?

Rings of electrons randomly embedded in a ball of positive charge.

What did the gold foil experiment determine? (Rutherford-Nucelar model)

That an atom is made up of mostly empty space and contained a small positively charged nucleus.

What did Niels Bohr discover? (Plentary model)

Electrons orbit the nucleus in distinct energy levels at specific distances.

What is the mass number (A)

The number of protons + neutrons in the nucleus.

What is the atomic number? (Z)

The number of protons in the nucleus. It is unique to each element.

What is an isotope?

Atoms which have the same number of protons but a different number of neutrons.

What is an ion?

A charged particle.

What are the 2 properties of isotopes?

They have similar chemical properties as the have the same electron structure + Slightly different physical properties due to different masses.

How do you calculate the mass of one particle?

Mass of one particle = Mass of 1 mole (relative mass)/ number of particles in 1 mole (6.022×10²³ )

What is the function of the TOF Mass Spectrometry

• Find the abundance and mass of all isotopes present in an element to determine its RAM.

• Find the relative molecular mass made of substances made of molecules.

Why is TOF Mass Spectrometry kept under a high vacuum?

To prevent the ions that are produced from colliding with molecules present in the air.

How does Electrospray Ionisation work?

1. The sample is dissolved in a volatile and polar solvent.

2. Injected at high pressure through a fine hollow needle connected to the positive terminal of a high voltage supply.

3. The particles are ionised by gaining a proton (H⁺ ) from the solvent, forming XH⁺ ions.

4. X _(g)+ H⁺ —> XH⁺_(g)

5. The solvent evaporates into the vacuum while the XH⁺ ions do not.

Why is Electrospray ionisation used with large organic molecules?

Because fragmentation does not occur.

How does Electron Impact work?

1. The sample being analysed is vaporised and injected at low pressure.

2. An electron gun fires high energy electrons at the sample.

3. This causes an electron to be knocked out from each particle, forming a 1⁺ ion

4. X_(g) —> X⁺_(g) + e^-

When is Electron Impact Ionisation used?

Elements and substances with low formula mass.

What happens in the acceleration stage?

The positive ions are accelerated to the same kinetic energy by an electric field towards a negatively charged plate.

Why do some ions travel faster than others?

They all have the same kinetic energy, however, ligher ions travel faster since their velocity depends on their mass.

What happens in the Flight tube?

The positive ions travel through a hole in the negatively charged plate into a tube. The time of flight of each particle depends on its velocity. The lighter ions reach the detector first.

What happens at the stage of detection?

The positive ions hit the negatively charged detection plate. This causes the ions to gain an electron which generates a movement of electrons and hence an electric current that is measured. The size of this current is proportional to the abundance of the species.

What is relative atomic mass?

Mean mass of one atom of an element/ 1/12^th mass of an atom of Carbon-12.

What is the relative molecular mass?

Mean mass of a molecule/ 1/12 mass of an atom of C-12