Has an atomic number double that of sodium’s. Has the lowest atomic number of any group 15 element. Is in group 1; has a higher atomic number than Cl but a lower atomic number than Br. Has between 35 and 55 protons and is in group 17. Has the lowest atomic mass on the periodic table. The atomic number is the number of protons in the nucleus of an atom. The number of protons define the identity of an element (i.e., an element with 6 protons is a carbon atom, no matter how many neutrons may be present). The number of protons determines how many electrons surround the nucleus, and it is the arrangement of these electrons that. The atomic mass of Hydrogen is 1.00797 amu and the atomic mass of Carbon is 12.011 amu. The atomic mass is typically listed in the periodic table below the element's name. Since isotopes have a different number of neutrons, thier mass numbers and atomic masses differ.

• Atomic Mass Number Of Helium
• Atomic Mass Number Of Carbon
• Atomic Number 8 And Mass Number 17
• Atomic Mass Number Calculator
• Atomic Mass Number 13
• Atomic Mass Number
• Atomic Mass Number Of Hydrogen

Learning Objective

• Determine the relationship between the mass number of an atom, its atomic number, its atomic mass, and its number of subatomic particles

Key Points

• Neutral atoms of each element contain an equal number of protons and electrons.
• The number of protons determines an element’s atomic number and is used to distinguish one element from another.
• The number of neutrons is variable, resulting in isotopes, which are different forms of the same atom that vary only in the number of neutrons they possess.
• Together, the number of protons and the number of neutrons determine an element’s mass number.
• Since an element’s isotopes have slightly different mass numbers, the atomic mass is calculated by obtaining the mean of the mass numbers for its isotopes.

Terms

• atomic massThe average mass of an atom, taking into account all its naturally occurring isotopes.
• mass numberThe sum of the number of protons and the number of neutrons in an atom.
• atomic numberThe number of protons in an atom.

Atomic Number

Neutral atoms of an element contain an equal number of protons and electrons. The number of protons determines an element’s atomic number (Z) and distinguishes one element from another. For example, carbon’s atomic number (Z) is 6 because it has 6 protons. The number of neutrons can vary to produce isotopes, which are atoms of the same element that have different numbers of neutrons. The number of electrons can also be different in atoms of the same element, thus producing ions (charged atoms). For instance, iron, Fe, can exist in its neutral state, or in the +2 and +3 ionic states.

Mass Number

An element’s mass number (A) is the sum of the number of protons and the number of neutrons. The small contribution of mass from electrons is disregarded in calculating the mass number. This approximation of mass can be used to easily calculate how many neutrons an element has by simply subtracting the number of protons from the mass number. Protons and neutrons both weigh about one atomic mass unit or amu. Isotopes of the same element will have the same atomic number but different mass numbers.

Scientists determine the atomic mass by calculating the mean of the mass numbers for its naturally-occurring isotopes. Often, the resulting number contains a decimal. For example, the atomic mass of chlorine (Cl) is 35.45 amu because chlorine is composed of several isotopes, some (the majority) with an atomic mass of 35 amu (17 protons and 18 neutrons) and some with an atomic mass of 37 amu (17 protons and 20 neutrons).

Given an atomic number (Z) and mass number (A), you can find the number of protons, neutrons, and electrons in a neutral atom. For example, a lithium atom (Z=3, A=7 amu) contains three protons (found from Z), three electrons (as the number of protons is equal to the number of electrons in an atom), and four neutrons (7 – 3 = 4).

Boundless vets and curates high-quality, openly licensed content from around the Internet. This particular resource used the following sources:

http://www.boundless.com/
Boundless Learning
CC BY-SA 3.0.

http://en.wiktionary.org/wiki/atomic_number
Wiktionary
CC BY-SA 3.0.

http://www.boundless.com//biology/definition/atomic-mass–2
Boundless Learning
CC BY-SA 3.0.

http://en.wikibooks.org/wiki/A-level_Chemistry/OCR/Atoms,_Bonds_and_Groups/Atoms_and_Reactions/Atoms
Wikibooks
CC BY-SA 3.0.

http://cnx.org/content/m44390/latest/?collection=col11448/latest
OpenStax CNX
CC BY 3.0.

Main Difference

The main difference between Atomic Mass and Atomic Number is that Atomic Mass is the total number of neutrons and protons in the nucleus of an atom, whereas Atomic Number is the total number of protons existing in the nucleus of an atom.

Atomic Mass Number Of Helium

Atomic Mass vs. Atomic Number

The total number of neutrons and protons that exist in the nucleus of an atom combine to make the mass of the atom known as its atomic mass. So, atomic mass is the average weight of an atom. On the flip side, the total protons numbers that are present in the atom’s nucleus known as the atomic number.

Atomic Mass Number Of Carbon

The atomic mass is also recognized as atomic weight whereas, and the atomic mass is also recognized as a proton number. The atomic mass is denoted by the letter ‘A.’ On the other hand, the atomic number denoted by the letter ‘Z.’ Atomic mass not used to differentiate between different elements. On the flip side, the atomic number used for the identification and classification of different elements. The atomic mass of an element can measure by using an atomic mass unit (amu). On the flip side, an atomic number is a number or a digit that can use to fix elements in a periodic table.

Atomic Number 8 And Mass Number 17

As the isotopes of an atom have the same number of protons but the different number of neutrons so, atomic mass can be used for the classification of different isotopes of an element. On the other side, all the isotopes of an element have the same atomic number so, it cannot use to classify them. For example, the atomic mass of carbon is twelve and thirteen for its two isotopes. On the flip side, its atomic number is six for all isotopes.

Comparison Chart

Atomic Mass Number Calculator

What is Atomic Mass?

Atomic mass is represented as the average weight of an atom and also recognized as atomic weight. An atom is composed of three subatomic particles, i.e., protons, neutrons, and electrons, as electrons are very light in weight, so the atomic mass considered as the mass of a total number of neutrons and protons present in the nucleus of an atom.

The letter ‘ A denotes the atomic mass.’ It expressed in the form of a unified atomic mass unit or ‘amu.’ One atomic mass unit is equal to 1/12 of the mass of a single C12 or carbon-12 atom with a value of 1.660 539 066 60(50) × 10⁻²⁷ kg. For example, the mass of a carbon-12 atom equaled to12 amu. As electrons are very light in weight, so, the mass of a carbon-12 isotope is composed of 6 neutrons and 6 protons. The protons and neutrons have the same mass so, it said that they both have a mass equal to 1 u.

As different isotopes of an atom vary in the number of neutrons. So, they all have different atomic mass. That is why atomic mass can use to identify different isotopes of an element. But, it is not used to differentiate between different elements. The atomic mass of an element can also find out by adding the number of the neutron in its atomic number.

What is the Atomic Number?

Atomic Mass Number 13

The atomic number is the total number of protons present in the nucleus of an atom. It also recognized as a proton number. It denoted by the letter ‘Z.’ As all the isotopes of an element have the same proton number so the atomic number cannot use to differentiate between the isotopes of that element.

The atomic number is used for the identification and classification of different elements. It is a number or a digit that can use to fix elements in a periodic table. Different elements are identified according to their specific atomic number and placed in the periodic table according to it.

For example, an atom that has atomic number 12 is carbon as it has 12 protons in its nucleus. An atom with different atomic numbers will be a different number. In the periodic table, all the elements arranged according to their increasing atomic number. So, the top most element present at the upper left corner of the table is hydrogen with atomic number 1. The next one is helium with atomic number 2 and so on.

As atomic mass is the number of protons and neutrons in the nucleus of an atom so, the atomic number can also find out by deducting the number of the neutron from the atomic mass of an element.

Key Differences

1. The total number of neutrons and protons existing in the nucleus of an atom is known as atomic mass whereas, the total number of protons present in the nucleus of an atom is known as the atomic number.
2. The atomic mass also recognized as atomic weight. On the flip side, the atomic number also recognized as a proton number.
3. The atomic mass represented as the average weight of an atom. On the other hand, the atomic number represents the total number of nucleon, i.e., protons in the nucleus.
4. The atomic mass is denoted by the letter ‘A.’ Conversely, the atomic number is denoted by the letter ‘Z.’
5. Isotopes of an atom have different atomic mass. On the flip side, the isotopes of an atom showing the same atomic number.
6. Atomic mass helps in the identification of different isotopes. On the other side, the atomic number cannot use to identify the different isotopes of an atom.
7. Atomic mass not used to differentiate between different elements, while the atomic number used for the identification and classification of different elements.
8. The atomic mass of an element can be measured by using an atomic mass unit (amu). On the other hand, an atomic number is a number or a digit that can use to fix elements in a periodic table.
9. The atomic mass of an element can find out by adding the number of the neutron in its atomic number, whereas; the atomic number can find out by deducting the number of the neutron from the atomic mass of an element.
10. The atomic mass of carbon is twelve and thirteen for its two isotopes. On the flip side, the atomic number of carbon atom is six for all isotopes.

Atomic Mass Number

Comparison Video

Atomic Mass Number Of Hydrogen

Conclusion

The above discussion summarizes that atomic mass is the average weight of an element that is equal to the number of its protons and neutrons in the nucleus. On the other side, the atomic number is the protons number present in the atom’s nucleus.