Final answer:
Not all elements in the same period as hydrogen have one valence electron, as the number of valence electrons varies across the period. Hydrogen is unique because it can lose, gain, or share an electron, resembling characteristics of both Group 1 and Group 17 elements.
Step-by-step explanation:
No, not all elements in the same row as hydrogen have one valence electron. In the periodic table, the number of valence electrons increases as you move from left to right across a period. Hydrogen, which is placed at the top of Group 1, has one valence electron. This is primarily because it has only one electron surrounding its nucleus. While hydrogen can be considered to belong to Group 1, where elements typically have one valence electron, it can also behave similarly to Group 17 elements (halogens) by gaining an electron to complete its valence shell. It is the unique position and behavior of hydrogen that make it able to form a positive ion (H+) like the alkali metals, share an electron to form a bond, or gain an electron to form a hydride ion (H−). However, other elements in the same period have a different number of valence electrons. For example, carbon in Group 14 has four valence electrons and oxygen in Group 16 has six valence electrons.