The sketch and explanation is attached below.
Explanation:
Matter consists of atom, which is the smallest particle of an elements. Atoms consists of three parts; The protons which are positively charged, the neutrons which are neutral and the electrons which are negatively charged. both the proton and neutron make up the nucleus while the electron orbit outside of the nucleus.
Protons ; are positively charged which form the basis of the atoms. the symbol for protons is Z and the number of protons which make up an atom is also known as the atomic number which is a unique property of an element, no two elements must have the same atomic number.
Neutrons ; are neutral in an atom as such they do not have a charge and it is indicated by the letter N. the number of protons is the difference between the mass number and the atomic number of the proton number.
Electrons ; are negatively charged and they orbit outside of the nucleus of an atom. The mass of a proton is 1840 times greater than the mass of an electron.
Various scientist have given their own explanation of the model of an atom, people like Ernest rutherford, Neil bohr, John Dalton, JJ Thompson et al came up with different postulation of the atomic model. Neil bohr for example said about electrons they they do not only have energy, but they have a particular energy which are confined into energy levels that is the energy of the electrons were quantised. John dalton -the English scientist also came about his atomic theory ; each element has its own unique type of atom, atoms of each individual element have the same atomic weight, when atoms combine, they do so in fixed ratios. although most of dalton's theory have been modified.
An electron shell on the other hand comprises of the outer part of an atom i.e outside the nucleus. shells have sub-shells or sublevels. there are K-L-M shells. sodium (Na) for example has an atomic number of 11 and an electronic configuration of 2)8)1 - this implies that it has 3-shells -k-L-M and the last electron in its shells which is 1 is known as the valence electrons or the outermost electron. it is the number of electron at the outermost shell that takes part in the donating and accepting of electron.
Calcium(Ca) for example has an atomic number of 20, electronic configuration 2)8)8)2, K-L-M-N, it has four shells. the outermost electron (2) is the valence electron and it is the electron which determines the group of an element. this explains why sodium (Na) is a group 1 element and calcium (Ca) is a group 2 elements.
The valence electrons is the only electron that takes part in sharing during bonding. for example Sodium chloride(Nacl) - sodium has 1 electron at the outermost shell and chlorine has 7 electron in its outermost shell, hence its needs 1 more electron to attain the octet state , this 1 electron will be donated by Na to become a cation as such sodium becomes the reducing agent and chlorine is the oxidizing agent as it accept electron to become a anion. The essence of bonding or transfer or sharing of electrons is for atoms of element to either attain the octet or duplet state.
