Chemical Ideas 2.1.

A simple model of the atom.

And around the nucleus?

Electrons

What’s inside?

In the nucleus?

Protons Neutrons

Location Mass How are they different?

Charge

p n e Mass on Ar scale 1 Charge +1 1 0 0.00055 -1

Nuclear symbols

Mass number =?

Atomic number =?

p + n

23 11

p?

Na

•11 •11 e ?

•12 n?

p ( = e )

What are isotopes?

17 35

Cl

p?

e ?

n?

17 17 18

37 17

Cl

p?

e ?

17 17 n?

20 •Atoms of the same element with: •The same atomic number but different mass numbers •Same number of protons but different numbers of neutrons

35

Cl

17

Cl-35 Why is

35

Cl O.K.?

Relative isotopic mass Chlorine always has an atomic number of 17! 17 37

Cl Cl-37

So what is relative atomic mass?

Cl-35

75%

Cl-37

25%

Relative atomic mass is the average of the relative isotopic masses Cl-35

75%

Cl-37

25% How do we get a relative atomic mass of 35.5?

The relative abundances .

What 2 things did we need to know?

Relative isotopic masses.

How do we find them out?

Use a mass spectromete r

Mass spectrometry

Sample in here Electric field Ionisation and fragmentation Magnetic field

e -

Mg +

e -

Sample in here Electric field

Cl-35 Cl-37

Ionisation and fragmentation Magnetic field

100 80 % 60 40 20 A mass spectrum … 35 36 37 mass

100 80 % 60 40 20 A mass spectrum … Try W and Y!

24 25 26 mass