The Bible does not say the serpent had a sexual union with Eve. The Bible plainly teaches that the serpent lied and tricked Eve into eating the forbidden fruit.
The account of Adam and Eve and the serpent in the Garden of Eden is found in Genesis, chapters 2 and 3. "The LORD God took the man and put him in the Garden of Eden to work it and take care of it. And the LORD God commanded the man, "You are free to eat from any tree in the garden; but you must not eat from the tree of the knowledge of good and evil, for when you eat of it you will surely die." (Gen. 2:15-17) After Adam had been in the Garden for a time, the Lord made a "suitable helper for him," a woman made from Adam's rib. (Gen. 2:20-22)
Adam and Eve must have been very happy in the Garden of Eden, a paradise where all their needs were taken care of and where they had perfect communion with God. But "the serpent was more crafty than any of the wild animals the LORD God had made. He said to the woman, 'Did God really say, You must not eat from any tree in the garden?' " After Eve responded that God had told them they must not eat of the one tree, or else they would die, the serpent told his first great lie, "You will not surely die." (Gen. 3:2-4)
Eve was deceived (or tricked); she ate the fruit, and gave some to Adam, who also ate it. Now they had to pay the consequences. In verses 17 to 19 of chapter 3, God told Adam he would now have a hard life, and in the end he would die. But God also pronounced judgment upon the serpent. One of the things God told the serpent was that, "I will put enmity between you and the woman, and between your offspring and hers; he will crush your head, and you will strike his heel." (Gen. 3:15) This was the first hint that God would eventually send a Savior and that the serpent would be destroyed.
But who was this serpent who could talk? In Revelation 20:2, pertaining to the last days, we read, "