Chemistry

    24– Mass number (Protons + Neutrons)
Mg
      12– Atomic number (Protons + Electrons)

                                         Relative mass                                     Charge

Proton                                     1                                                       +1

Neutron                                   1                                                        0

Electron                            Very small                                               -1

Atoms are neutral because they have equal number of Protons and electrons so cancel each ther out.

Isotopes
It is an copy of an atom,same number of Protons/electrons but not neutrons.

12 13
C C                   Reaction same because same number of electrons. Carbon 13
6 6                    Will be heavier because it has more neutrons which control mass.
P=6 P=6
E=6 E=6
N=6 N=7

➖1 electron in outer shell

➖Called alkali metals because very reactive

➖React rapidly with oxygen, chlorine and water

As you go down it gets more reactive because......

➖ Outer electron is further from nucleus so less attraction and easier to lose.