Answer:
a. 
b. 
c. 
d. 
Explanation:
Given lithium with atomic mass (M = 7) and atomic number (Z = 3), we may write it in a standard notation placing the atomic mass as a superscript and the atomic number as a subscript:
a. Atomic number corresponds to the total number of protons a species has. Adding a proton to lithium would increase the atomic number by 1 unit. Besides, changing the atomic number would also change the element, as each element has a unique atomic number.
It's also important to remember that mass of an atom consists of a sum of protons and neutrons, so we'd also have to add 1 to the mass number. Therefore, we would have some species X with:
Now we need to identify X finding an element with Z = 4 in the periodic table. This is beryllium:
b. Standard lithium atom has an atomic number of 3, this means it has 3 protons. Since we have an atom, the positive charge provided by protons is equal to the negative charge provided by electrons. This implies that a neutral atom has the same number of protons and electrons.
We start with 3 electrons in lithium. Removing an electron would produce a lithium cation with a +1 charge, as we now have a net charge of +3 from protons and -2 from electrons.
Therefore, we may represent this as lithium cation with a +1 charge:
c. Neutrons don't have a charge but they are a component of the total mass an atom has. Essentially, adding a neutron wouldn't change the overall charge (the atomic number) of lithium.
However, adding a neutron would cause the mass to increase by 1, as each neutron (as well as proton) weighs 1 atomic mass unit. Since the atomic number doesn't change, the element would still be lithium in that case:
d. Firstly, we remove a proton, this means the atomic number of Li decreases by 1 unit, as an atomic number is equal to the number of protons:
The mass would also decrease by 1 unit, as mass contains the number of protons and neutrons:
That said, upon performing the first step, we have helium (atomic number of 2 in the periodic table) with a mass of 6:
Now, we also remove 2 neutrons. This means the mass decreases by 2 units and the charge of He remains constant, as no protons are involved in this step and neutrons don't change the charge of a nucleus:
Finally, an electron is removed. Removing an electron would produce a helium cation with charge +1, as we'd have 2 protons and 1 remaining electron upon removing 1 electron from helium that has a total of 2 electrons in its atomic state:
