Atoms have a central nucleus of protons and neutrons.
The crossover method is a way to determine the chemical formula of compounds using the valence of atoms. Atoms have a central nucleus of protons and neutrons, with shells of electrons surrounding the nucleus in shells called shells. The outermost shell may contain many or few electrons, which is described by a positive or negative valence number. Compounds are formed by exchanging these electrons in reactions called ionic bonds, in which two or more atoms share electrons.
When an atom with two extra electrons combines with an atom with one less electron, it takes two from the second atom to form the compound. Silicon contains two extra electrons in its outer shell, while oxygen contains one less electron than a full shell. The ionic formula of the two atoms would be Si & plus; 2 and O −1 , showing the ionic valence of each.
Using the crossover method, the resulting compound can be written by transferring the valence of each atom to the other and writing them as a subscript. The resulting molecule from the combination of silicon and oxygen is silicon dioxide or SiO 2 . The valence & plus; The 2 of the silicon atom crosses over with the oxygen and the −1 is transferred or crosses over with the silicon. Crossing the valences between the two atoms when describing the molecule led to the term crossover method.
The reaction of the two atoms removes any electronic charge, because the atoms combine in the proportions necessary to use up all of the excess electrons. With a balanced number of electrons, the valence is considered zero and no plus or minus sign is used in a molecular formula. Ionic molecules tend to be very stable because electrons are shared between atoms, forming a very strong chemical bond.
A process called reduction is used to create the proper molecular name when the ionic valences are multiples of smaller numbers. Barium and oxygen can combine to form barium oxide, with each of the atoms having a valence of two. Using the cross method, the valence of 2 would be crossed with the atomic name of the other atom, resulting in a molecule called Ba 2 O 2 . The subscripts can be divided by 2, so the correct molecule is BaO and the valences have been reduced to the minimum necessary.
The cross method also works when the molecules are made up of more complex groups, such as zinc acetate. Zinc (Zn) with valence & plus; 2, can chemically combine with an acetate molecule (C 2 H 3 O 2 ) with a valence of -1. The method alternates the two valences to show that one zinc atom will combine with two acetate molecules to form Zn(C 2 H 3 O 2 ) 2 . As long as the molecule has a known valence, the crossover method can be used to determine the correct molecular structure of any compound.