Year 12s: what will be the first way you research your future options? >>

Chemistry - help

I'm so confused with the definition of Atomic number and Mass number, also when there's an isotope how does the mass number change?

Reply 1

Yazomi

Original post by TrishaChou1

I'm so confused with the definition of Atomic number and Mass number, also when there's an isotope how does the mass number change?

Atomic number is the number of protons
Mass number/atomic mass = protons+neutron

Every single element has a unique number of protons ie an element that has 12 protons can only be carbon and nothing else.

Isotopes are when the proton number is the same and therefore same element, but they have different number of neutrons.
Therefore atomic mass vary depending on the difference in neutron number

Mass of proton =1.
Mass of neutron =1.

Reply 2

TrishaChou1

Original post by Yazomi

hey thank you so much x

Reply 3

EierVonSatan

Relative atomic mass and mass number are different.

Mass number = number of protons and neutrons added together - so it's always a whole number!
Relative atomic mass = the weighted average of the mass numbers of all of the isotopes - will often be a decimal e.g. Cl has an Ar of 35.5 since it is made from 25% 37Cl and 75% 35Cl

Reply 4

arkadi342

Original post by TrishaChou1

I'm so confused with the definition of Atomic number and Mass number, also when there's an isotope how does the mass number change?

the atomic number is the number of protons (which is the same as the number of electrons, unless it's an ion)
the mass number is the number of both protons and neutrons (so is the bigger number)
an isotope is an atom of an element that has a different number of neutrons, but the same number of protons and electrons, to most atoms of that elemet.
an isotope will have the same atomic number, but a different mass number.