Atoms and the Periodic table

Page
2

Slide 9

Nuclide notation – how many protons, neutrons, and electrons in ions?

23

Mass number

(protons + neutrons)

Na+

11

Atomic number

(number of protons)

–

12

number of neutrons

1+ charge means 1 electron less than the number of protons. This atom has 10 electrons.

Slide 10

Nuclide notation – how many protons, neutrons, and electrons in ions?

16

Mass number

(protons + neutrons)

O2–

8

Atomic number

(number of protons)

–

8

number of neutrons

2– charge means 2 electrons more than the number of protons. This atom has 10 electrons.

Slide 11

Isotopes.

Isotopes are:

atoms of the same element

which have different mass numbers

due to different numbers of neutrons in each nucleus.

Most elements exist as a mixture of isotopes, e.g. chlorine has 2 isotopes

35

Cl

17

37

Cl

17

Slide 12

Relative atomic mass

The relative atomic mass of an element is the average mass of all the isotopes of that element.

The relative atomic mass of chlorine is 35.5. Chlorine has 2 isotopes

35

Cl

17

37

Cl

17

so the isotope of mass 35 is present in the largest quantity.