# Important Differences between Atomic mass and Atomic number

Atomic Mass

Atomic mass, also known as atomic weight, is a fundamental property of an element. It represents the average mass of an atom of that element, taking into account all its naturally occurring isotopes and their relative abundances. Atomic mass is typically expressed in atomic mass units (amu) and is relative to the mass of a carbon-12 atom, which is defined as exactly 12 amu. The atomic mass of an element is crucial in various chemical calculations, including stoichiometry and determining the molar mass of compounds. It is found on the periodic table, where each element is listed with its atomic number and atomic mass. This value provides valuable information about the element’s mass and composition, aiding in chemical understanding and experimentation.

Atomic mass Formula

The atomic mass of an element is calculated by taking the weighted average of the masses of all naturally occurring isotopes of that element, with the weights being the relative abundances of each isotope. The formula to calculate atomic mass is as follows:

Atomic mass = Mass of protons + Mass of neutrons + Mass of electrons

Atomic Mass=(m1​⋅a1​)+(m2​⋅a2​)+…+(mn​⋅an​)

Where:

• mi = Mass of isotope i (in atomic mass units, amu)
• ai = Abundance (or relative abundance) of isotope �i (expressed as a decimal)

This formula accounts for all naturally occurring isotopes of the element. The atomic mass unit (amu) is defined based on the carbon-12 isotope, where one amu is approximately equal to the mass of one twelfth of a carbon-12 atom.

For example, consider the element carbon, which has two naturally occurring isotopes: carbon-12 and carbon-13. The atomic mass of carbon is approximately 12.011 amu. This value is calculated by considering the mass of carbon-12 (99% abundance) and carbon-13 (1% abundance).

How to Calculate Atomic Mass?

• Obtain Isotopic Data:

Determine the naturally occurring isotopes of the element and their respective abundances. This information is typically available in reference materials or on the periodic table.

• Convert Abundance to Decimal:

Express the abundance of each isotope as a decimal. For example, if an isotope has an abundance of 20%, it is written as 0.20.

• Multiply Mass and Abundance:

For each isotope, multiply its mass (in atomic mass units, amu) by its relative abundance.

• Sum the Products:

Add together all the results obtained in step 3.

• Round to Appropriate Decimal Places:

Round the final result to the appropriate number of decimal places based on the level of precision required.

Here’s an example using carbon:

• Carbon-12 (98.93% abundance, 12.0000 amu)
• Carbon-13 (1.07% abundance, 13.0034 amu)

Calculation:

Atomic Mass = (12.0000×0.9893) + (13.0034×0.0107) ≈ 12.011amu

Atomic Mass of Elements

 Element Atomic Mass (amu) Hydrogen 1.008 Helium 4.0026 Carbon 12.011 Nitrogen 14.007 Oxygen 15.999 Sodium 22.990 Magnesium 24.305 Silicon 28.085 Sulfur 32.06 Chlorine 35.45 Potassium 39.098 Iron 55.845 Copper 63.546 Zinc 65.38 Bromine 79.904 Silver 107.868 Iodine 126.904

Relative Atomic Mass

The relative atomic mass (also known as atomic weight) of an element is the weighted average of the masses of all naturally occurring isotopes of that element, taking into account their relative abundances. It is expressed in atomic mass units (amu).

The concept of relative atomic mass is crucial in chemistry because most elements exist as a mixture of isotopes. Since different isotopes have different masses, the relative abundance of each isotope affects the overall atomic mass of the element.

For example, the atomic mass of carbon is approximately 12.011 amu. This value is an average that considers the proportions of carbon-12 (98.93% abundance) and carbon-13 (1.07% abundance).

The relative atomic mass is listed on the periodic table beneath the symbol of each element. It provides a more accurate representation of the typical mass of an atom of that element compared to using a single isotope’s mass.

Atomic number

The atomic number is a fundamental property of an element, denoted by the symbol “Z”. It represents the number of protons present in the nucleus of an atom. This defining characteristic is unique to each element, distinguishing one element from another. Elements are arranged in ascending order of atomic number on the periodic table. It determines the chemical identity of an element, as atoms with different atomic numbers have distinct properties. Additionally, the atomic number indirectly influences the arrangement of electrons in energy levels, further impacting an element’s reactivity and behavior in chemical reactions. In summary, the atomic number is a cornerstone in understanding the organization, classification, and behavior of elements in the realm of chemistry.

Atomic number Properties

• Unique Identifier:

The atomic number is a unique identifier for each element. No two elements have the same atomic number.

• Determines Element’s Identity:

The number of protons (and hence the atomic number) is what defines an element. Changing the number of protons changes the element itself.

• Organizes Elements:

Elements are arranged in the periodic table based on their atomic numbers. This arrangement groups elements with similar properties together.

• Electron Configuration:

The atomic number determines the number of electrons in a neutral atom and influences the electron configuration.

• Chemical Properties:

Elements with similar atomic numbers tend to have similar chemical properties due to similar electronic structures.

• Isotope Identification:

Isotopes of an element have the same atomic number but different mass numbers. This allows for easy identification of isotopes.

• Nuclear Stability:

The atomic number plays a role in determining nuclear stability. Elements with too many or too few protons relative to neutrons may undergo radioactive decay.

• Nuclear Reactions:

In nuclear reactions, the atomic number is conserved. This means the total atomic number before and after a reaction remains the same.

• Binding Energy:

The atomic number affects the binding energy of a nucleus, which is crucial in understanding nuclear processes.

• Fusion and Fission:

Atomic number considerations are critical in nuclear fusion and fission reactions, where elements may change due to nuclear transformations.

• Nuclear Physics:

In nuclear physics, the atomic number is a key parameter for understanding nuclear structure and behavior.

List of Atomic Numbers

 Atomic Number Symbol Element 1 H Hydrogen 2 He Helium 3 Li Lithium 4 Be Beryllium 5 B Boron 6 C Carbon 7 N Nitrogen 8 O Oxygen 9 F Fluorine 10 Ne Neon 11 Na Sodium 12 Mg Magnesium 13 Al Aluminum 14 Si Silicon 15 P Phosphorus 16 S Sulfur 17 Cl Chlorine 18 Ar Argon 19 K Potassium 20 Ca Calcium 21 Sc Scandium 22 Ti Titanium 23 V Vanadium 24 Cr Chromium 25 Mn Manganese 26 Fe Iron 27 Co Cobalt 28 Ni Nickel 29 Cu Copper 30 Zn Zinc 31 Ga Gallium 32 Ge Germanium 33 As Arsenic 34 Se Selenium 35 Br Bromine 36 Kr Krypton 37 Rb Rubidium 38 Sr Strontium 39 Y Yttrium 40 Zr Zirconium 41 Nb Niobium 42 Mo Molybdenum 43 Tc Technetium 44 Ru Ruthenium 45 Rh Rhodium 46 Pd Palladium 47 Ag Silver 48 Cd Cadmium 49 In Indium 50 Sn Tin 51 Sb Antimony 52 Te Tellurium 53 I Iodine 54 Xe Xenon 55 Cs Cesium 56 Ba Barium 57 La Lanthanum 58 Ce Cerium 59 Pr Praseodymium 60 Nd Neodymium 61 Pm Promethium 62 Sm Samarium 63 Eu Europium 64 Gd Gadolinium 65 Tb Terbium 66 Dy Dysprosium 67 Ho Holmium 68 Er Erbium 69 Tm Thulium 70 Yb Ytterbium 71 Lu Lutetium 72 Hf Hafnium 73 Ta Tantalum 74 W Tungsten 75 Re Rhenium 76 Os Osmium 77 Ir Iridium 78 Pt Platinum 79 Au Gold 80 Hg Mercury 81 Tl Thallium 82 Pb Lead 83 Bi Bismuth 84 Po Polonium 85 At Astatine 86 Rn Radon 87 Fr Francium 88 Ra Radium 89 Ac Actinium 90 Th Thorium 91 Pa Protactinium 92 U Uranium 93 Np Neptunium 94 Pu Plutonium 95 Am Americium 96 Cm Curium 97 Bk Berkelium 98 Cf Californium 99 Es Einsteinium 100 Fm Fermium 101 Md Mendelevium 102 No Nobelium 103 Lr Lawrencium 104 Rf Rutherfordium 105 Db Dubnium 106 Sg Seaborgium 107 Bh Bohrium 108 Hs Hassium 109 Mt Meitnerium 110 Ds Darmstadtium 111 Rg Roentgenium 112 Cn Copernicium 113 Nh Nihonium 114 Fl Flerovium 115 Mc Moscovium 116 Lv Livermorium 117 Ts Tennessine 118 Og Oganesson

How to Find the Atomic Number

• Consult the Periodic Table:

The periodic table is a valuable resource for finding atomic numbers. Each element is listed along with its chemical symbol and atomic number.

• Locate the Element:

Find the element you are interested in on the periodic table. The atomic number is usually located above or below the chemical symbol of the element.

The atomic number is a whole number typically written above the chemical symbol. It is usually found in the top left corner of the box representing the element.

For example, for oxygen, the atomic number is 8. In the periodic table, it is located above the chemical symbol “O”.

Important Differences between Atomic mass and Atomic number

 Basis of Comparison Atomic Mass Atomic Number Definition Average mass of atom, including isotopes Number of protons in an atom Unit of Measure Atomic Mass Units (amu) Dimensionless Determines Identity No two elements have the same atomic mass Defines the element’s identity Represented on PT Not represented directly on periodic table Listed in each element’s box Contribution to Mass Contributes to the mass of an atom Doesn’t contribute to mass directly Variable Values Can vary due to isotopic composition Unique, fixed value for each element Calculation Basis Involves all isotopes and their abundances Independent of isotopic composition Influence on Behavior Affects physical properties and behavior Doesn’t directly influence behavior Relative Comparison Provides a relative measure of an element’s mass No relative comparison based on number Isotopic Consideration Considers all isotopes’ masses and abundances Not influenced by isotopic composition Role in Chemistry Important in stoichiometry, molar mass calculations Defines chemical identity, influences bonding Numerical Magnitude Usually a decimal value, not a whole number Always a whole number Location on PT Not explicitly shown on periodic table Shown prominently for each element Relation to Neutrons Related to the total number of protons and neutrons Not directly related to neutron count Notation in Symbol Not included in chemical symbol Not part of the chemical symbol

Important Similarities between Atomic mass and Atomic number

• Both Define an Element:

Both atomic mass and atomic number are properties that uniquely define an element. They are fundamental characteristics of an element.

• Relevance to the Periodic Table:

Both atomic mass and atomic number are used in the organization of elements on the periodic table. Elements are arranged based on increasing atomic number, and atomic mass is included in the detailed information provided for each element.

• Influence on Chemical Behavior:

Both properties have an impact on the chemical behavior of an element. Atomic number determines the element’s identity and its electron arrangement, while atomic mass affects stoichiometry and molar mass calculations.

• Applicability in Chemistry:

Both atomic mass and atomic number are crucial concepts in chemistry. They are used in a wide range of calculations and chemical analyses.

• Standard Units:

Both properties have standardized units. Atomic mass is expressed in atomic mass units (amu), and atomic number is a dimensionless quantity.

• Used in Nuclear Physics:

Both properties are important in nuclear physics. Atomic number is directly related to the number of protons, and atomic mass is relevant in nuclear reactions and processes.

• Role in Isotope Identification:

Both properties are used in identifying isotopes of an element. Isotopes have the same atomic number but different atomic masses.

• Basic Information on the Periodic Table:

Both atomic mass and atomic number are prominently displayed on the periodic table for each element, providing key information about the element’s identity and mass.

Disclaimer: This article is provided for informational purposes only, based on publicly available knowledge. It is not a substitute for professional advice, consultation, or medical treatment. Readers are strongly advised to seek guidance from qualified professionals, advisors, or healthcare practitioners for any specific concerns or conditions. The content on intactone.com is presented as general information and is provided “as is,” without any warranties or guarantees. Users assume all risks associated with its use, and we disclaim any liability for any damages that may occur as a result.

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