Your science teacher may have provided you with incorrect information regarding the atomic number and its relationship to the rounded atomic mass. The atomic number of an element does not change. It is a fundamental property of an element and represents the number of protons in the nucleus of an atom of that element.
In a Bohr model, the atomic number is represented by the number of protons in the nucleus, while the atomic mass represents the total number of protons and neutrons in the nucleus. However, the atomic mass is not rounded when determining the number of electrons in a Bohr model.
To create a Bohr model, you typically represent the electrons in energy levels or shells surrounding the nucleus. The number of electrons in a neutral atom is equal to the atomic number. For example, hydrogen (atomic number 1) has one electron in its Bohr model, while helium (atomic number 2) has two electrons.
The atomic mass, on the other hand, is often presented as a decimal value on the periodic table. This is because the atomic mass represents the average mass of all naturally occurring isotopes of an element, taking into account their relative abundance. It is not necessary to subtract the rounded atomic mass from the atomic number when constructing a Bohr model.
It's important to rely on accurate and up-to-date sources for scientific information. If you have any doubts or questions, it's a good idea to consult additional reputable sources or ask your science teacher for clarification.