[shanker]

I am confused on some homework. We have to fill in a grid with various pieces missing to do with the structure of atoms and ions but i am having difficulty completing 3 questions.
1.i am given the atomic number is 82 so it is lead. however i am also told there are 126 neutrons, could this be a typing error

2.I am given the atomic number is 35 so i know it is bromine but the number of neutrons given is 44 however if i was to add 35 and 44 i get 79, which is less than the mass number shown on the periodic table.


3.the last problem is with the same element. we are given the atomic number to be 35 and the number of neutrons to be 46 however that gives a total of 81, still not equal to 80.


can you please confirm whether these are typing errors or i am missing something to do with the addition or loss of neutrons within an element which i don't know about.

[Sam (NG)]

There are no mistakes in your questions.

The periodic table does not give you the mass number of elements.  It gives the relative atomic mass.

What is an isotope?

[shanker]

an isotope is an an element with the same number of protons but a different number of neutrons, yeah i understand now. how do you find the mass number when you are given the atomic number to be 35 and number of neutrons to be 44 ? i really don't understand,

[Sam (NG)]

You were calculating the mass number previously, and assuming it to be equivalent to relative atomic mass, which it isn't.

Relative atomic mass is the average atomic mass of that element, taking into account the natural isotopic abundancies.

[shanker]

is a neutron equal to one? if  this is the case do you mind checking one question?

Given
Atomic number:35
Number of neutrons:44

Worked out
Number of protons:35
Number of electrons:35
Atom / ion: Br ??
Mass number: 79??


I am most unsure about whether the atomic symbol needs a charge to show it is an isotope or if it is left as just the elemental symbol and if i have added the protons and neutrons up correctly given they are the correct amount of each (i hope).

[Sam (NG)]

The answer is correct.

The symbol for a particular isotope can be written the same as you write the element in the periodic table, taking Bromine for example:

meh, can't get latex to show what I want, I'll draw it:

[shanker]

That is very helpful. Thank-you Sam (UoN) 

[shanker]

Oh I see, so when writing the elemental symbol of an isotope you don't write the relative atomic mass, but the isotope's mass. Seems logical, I'm just a bit stupid I guess.

[renge ishyo]

Seems logical, I'm just a bit stupid I guess.

You guess wrong. Stupidity is a pattern of behavior. It has nothing to do with whether you happen to understand a certain topic easily or not.