protons
valence electrons
shells
Atoms in the same group (in the same vertical column) of the periodic table have the same number of electrons in their outer shell. A neutral atom has the same number of electrons as it has protons. The number of protons is given by it's atomic number. The electrons are considered to be arranged in "shells." The outermost shell can have from 1 to 8 electrons. The effect of being in the same group is that the atoms within a group have similar reactions.
Such atoms belong to a group in the periodic table of elements.
The atoms of the elements in the same group have the same number of valence electrons. This means that they react with other elements in a similar way. For example group 1. All the atoms in group 1 react with water and oxygen, so they have to be kept in paraffin-oil. Another example is group 18. They don't react with anything. The atoms of the same row have the same electron shells.
Atoms of the elements in a group have the same number of electrons in their outer energy shells. This gives the elements similar Chemical Propetries.
atoms in a group have the same number of valence electrons
number of valence electrons
The atoms of elements in Group 2 have the same number of valence electrons, which is 2. This gives them similar chemical properties, such as forming 2+ cations in reactions.
Atoms of the same element cannot have different numbers of protons. Different numbers of protons mean different elements. An atom with the a different number of neutrons is called an isotope.
All atoms with the same number of protons are atoms of the same element. The number of protons is the atomic number of the element.
They share the same number of electrons (=2) in the valence shell: they have the same oxidation state of +2