A zygote is the initial cell formed after a sperm and egg have joined. A blastocyst begins at day 5 in mammals after fertilization. This all occurs during the first week of being conceived. After the first week, the developing life form becomes an embryo, and the embryo is the stage where DNA is built..After week 9 in a human lifeform, it is considered a fetus. zygote is the initial cell formed after a sperm and egg have joined. A blastocyst begins at day 5 in mammals after fertilization. This all occurs during the first week of being conceived. After the first week, the developing life form becomes an embryo, and the embryo is the stage where DNA is built..
A covalent chemical bond results from the sharing of electrons between two atoms with similar electronegativities A single covalent bond represent the sharing of two valence electrons (usually from two different atoms). The Lewis structure below represents the covalent bond between two hydrogen atoms in a H2 molecule.
Valence electron. In chemistry, a valence electron is an electron that is associated with an atom, and that can participate in the formation of a chemical bond; in a single covalent bond, both atoms in the bond contribute one valence electron in order to form a shared pair.