Why do atoms of the same element always have the same atomic number but have different mass numbers?

Answer 1

An isotope is an atom that has different numbers of neutrons compared to its protons. So each variation of neutron numbers will give it a different mass number, but will still retain its atomic number.

Answer 2

Atoms of the same element have the same number of protons, which determines their atomic number, but can have different numbers of neutrons, which results in different mass numbers. This variation in neutron number forms isotopes of the same element with different mass numbers.

Answer 3

The atomic number of an element refers to the number of protons in its nucleus, and this number never varies - an atom with a different number of protons is a differentelement. But, the number of neutrons in an atom of the same element can vary. An atom of the same element with a different number of neutrons is called an isotope. In isotopes, the mass number refers to the number of protons plus the number of neutrons in the nucleus of the atom. mass number = atomic number + number of neutrons For example, chlorine (Cl) has 17 protons, so its atomic number is 17. But there are isotopes of chlorine that can have either 18 or 20 neutrons, each giving chlorine a different mass number. So the two isotopes of chlorine are: 17 + 18 = mass number 35 17 + 20 = mass number 37 [Note: There are a number of other isotopes of chlorine, but these common ones are cited for examples.]

Answer 4

The mass of an atom is almost all in the nucleus of the atom; this is the small positively charged bit in the middle that the electrons buzz around. When we talk about the mass of an atom it is the nucleus we are interested in. The nucleus of an atom is made up of protons and neutrons. Protons are the positively charged particles in the nucleus and they are what decide what the atom is. Hydrogen has 1 proton, helium has 2 protons, lithium has 3, iron has 26, gold has 79 and so on. If it has 1 proton it is hydrogen, if it has 79 protons it is gold. Each element has its own unique number of protons. Unfortunately its not quite that simple, if there were only protons in the nucleus then hydrogen would have an Atomic Mass of 1, helium 2, gold 79, etc. but there are neutrons as well. This means the weights don't go up by 1 each time, it depends how many neutrons the element tends to have but the weight does keep going up as you move through the table.

Answer 5

It happens for most elements that you can get one or two or more extra/fewer neutrons in the nucleus. These are uncharged so the proton/electron counts are identical, and they are chemically practically identical. Called "isotopes".

Answer 6

The atomic number of an element tells you how many protons an atom has in it's nucleus, and each element is defined by the number of protons it has. For example hydrogen always has 1 proton.

The Mass number tells you how many protons and neutrons there are in an atom. However it is possible for an element to have different numbers of neutrons in the nucleus. When this occurs you will get different masses for the same element but the same atomic number.

Two (or more) elements are known as isotopes if the only difference between them is the number of neutrons.

Probably the most common/well known example of an isotope is Hydrogen, Deuterium (Hydrogen with a neutron) and Tritium (Hydrogen with 2 neutrons)

Answer 7

"Same element" means the nucleus has the same number of protons, and that defines the element. But the number of neutrons in the nucleus can differ from one atom to another within nuclei of a given element. These atoms with "variant" nuclei are called isotopes of the element, with the mass number being the sum of protons and neutrons in the nucleus. (A neutron has mass almost the same as the mass of a proton).

Answer 8

Different isotopes of the same element have different masses, due to them having different amounts of neutrons.

For example, the most common isotope of Hydrogen, protium, has one Proton and one Neutron, giving it a mass number of 1. Another isotope of Hydrogen, tritium, has one Proton and three neutrons, giving it a mass number of 4.

Answer 9

Different isotopes have different numbers of neutrons so their mass numbers are different.

Answer 10

The number of neutrons can vary for an element, creating atoms of different weights which are known as isotopes.