Atomic Numbers

2/14/2022by admin

Atomic mass number determines especially the atomic mass of atoms. The mass number is different for each different isotope of a chemical element. The mass number is written either after the element name or as a superscript to the left of an element’s symbol. For example, the most common isotope of carbon is carbon-12, or 12 C. Atomic number The number of protons in the nucleus of an atom. In electrically neutral atoms, this number is also equal to the number of electrons orbiting about the atom's nucleus.

  1. The Elements, Sorted By Atomic Number - Angelo State University
  2. Atomic Numbers 8
  3. Atomic Numbers Of Elements
1HydrogenH
2HeliumHe
3LithiumLi
4BerylliumBe
5BoronB
6CarbonC
7NitrogenN
8OxygenO
9FluorineF
10NeonNe
11SodiumNa
12MagnesiumMg
13AluminumAl
14SiliconSi
15PhosphorusP
16SulfurS
17ChlorineCl
18ArgonAr
19PotassiumK
20CalciumCa
21ScandiumSc
22TitaniumTi
23VanadiumV
24ChromiumCr
25ManganeseMn
26IronFe
27CobaltCo
28NickelNi
29CopperCu
30ZincZn
31GalliumGa
32GermaniumGe
33ArsenicAs
34SeleniumSe
35BromineBr
36KryptonKr
37RubidiumRb
38StrontiumSr
39YttriumY
40ZirconiumZr
41NiobiumNb
42MolybdenumMo
43TechnetiumTc
44RutheniumRu
45RhodiumRh
46PalladiumPd
47SilverAg
48CadmiumCd
49IndiumIn
50TinSn
51AntimonySb
52TelluriumTe
53IodineI
54XenonXe
55CesiumCs
56BariumBa
57LanthanumLa
58CeriumCe
59PraseodymiumPr
60NeodymiumNd
61PromethiumPm
62SamariumSm
63EuropiumEu
64GadoliniumGd
65TerbiumTb
66DysprosiumDy
67HolmiumHo
68ErbiumEr
69ThuliumTm
70YtterbiumYb
71LutetiumLu
72HafniumHf
73TantalumTa
74TungstenW
75RheniumRe
76OsmiumOs
77IridiumIr
78PlatinumPt
79GoldAu
80MercuryHg
81ThalliumTl
82LeadPb
83BismuthBi
84PoloniumPo
85AstatineAt
86RadonRn
87FranciumFr
88RadiumRa
89ActiniumAc
90ThoriumTh
91ProtactiniumPa
92UraniumU
93NeptuniumNp
94PlutoniumPu
95AmericiumAm
96CuriumCm
97BerkeliumBk
98CaliforniumCf
99EinsteiniumEs
100FermiumFm
101MendeleviumMd
102NobeliumNo
103LawrenciumLr
104RutherfordiumRf
105DubniumDb
106SeaborgiumSg
107BohriumBh
108HassiumHs
109MeitneriumMt
110DarmstadtiumDs
111RoentgeniumRg
112CoperniciumCn
113NihoniumNh
114FleroviumFl
115MoscoviumMc
116LivermoriumLv
117TennessineTs
118OganessonOg

Download a printable version of the Periodic Table of Elements in PDF format:

- Color: Basic / Advanced

- Black and White: Basic / Advanced

The following on-line games based on the Periodic Table of Elements are available:

- Element Flash Cards

- Element Hangman

- Element Matching

- Element Math

- Element Crossword Puzzles

- Element Concentration

- Element Balancing

- Element Word Scramble

The following paper-based activities are available:

- Element BINGO

- Element Word Search

In addition to the information contained within the Periodic Table of Elements, the following articles may be helpful if you are writing a report about an element or if you are making a model of an atom:

- How to calculate the number of protons, neutrons and electrons in an atom of an element

- How to make a model of an atom

- How to draw an atom (video)

- How to read an electron configuration chart

- A list of who discovered each element

The information on this site has been compiled from a number of sources.

For questions about this page, please contact Steve Gagnon.

Athletes wearing the same-colored jerseys are all on the same team. In addition, each player’s jersey has a unique number to distinguish him from his teammates. Imagine how confusing it would be if members of both teams wore the same-colored jerseys or all the members of a team had the same number on their jerseys. How could you tell the athletes apart?

The Elements, Sorted By Atomic Number - Angelo State University


TellingAtomsApart

It’s often useful to have ways to signify different people or objects like athletes on teams. The same is true of atoms. It’s important to be able to distinguish atoms of one element from atoms of other elements. Elements are pure substances that make up all other matter, so each one is given a unique name. The names of elements are also represented by unique one- or two-letter symbols, such as H for hydrogen, C for carbon, and He for helium. You can see other examples in the Figure below.

Q:The table shown in the Figure above is called the periodic table of the elements. Each symbol stands for a different element. What do you think the symbol K stands for?

A: The symbol K stands for the element potassium. The symbol comes from the Latin name for potassium, which is kalium.

The symbols in the Figure above would be more useful if they revealed more information about the atoms they represent. For example, it would be useful to know the numbers of protons and neutrons in the atoms. That’s where atomic number and mass number come in.

Atomic Number

The number of protons in an atom is called its atomic number. This number is very important because it is unique for atoms of a given element. All atoms of an element have the same number of protons, and every element has a different number of protons in its atoms. For example, all helium atoms have two protons, and no other elements have atoms with two protons. In the case of helium, the atomic number is 2. The atomic number of an element is usually written in front of and slightly below the element’s symbol, like in the Figure below for helium.

Atoms are neutral in electrical charge because they have the same number of negative electrons as positive protons. Therefore, the atomic number of an atom also tells you how many electrons the atom has. This, in turn, determines many of the atom’s properties.

Mass Number

There is another number in the Figure above for helium. That number is the mass number, which is the mass of the atom in a unit called the atomic mass unit (amu). One atomic mass unit is the mass of a proton, or about 1.67 × 10-27 kilograms, which is an extremely small mass. To better appreciate how small an atomic mass unit is, go to this

URL:http://www.colorado.edu/physics/2000/periodic_table/atomic_mass.html.

A neutron has just a tiny bit more mass than a proton, so its mass is often assumed to be one atomic mass unit as well. Because electrons have virtually no mass, just about all the mass of an atom is in its protons and neutrons. Therefore, the total number of protons and neutrons in an atom determines its mass in atomic mass units.

Consider helium again. Most helium atoms have two neutrons in addition to two protons. Therefore the mass of most helium atoms is 4 atomic mass units (2 amu for the protons + 2 amu for the neutrons). However, some helium atoms have more or less than two neutrons. Atoms with the same number of protons but different numbers of neutrons are called isotopes. Because the number of neutrons can vary for a given element, the mass numbers of different atoms of an element may also vary. For example, some helium atoms have three neutrons instead of two. Therefore, they have a different mass number than the one given in the Figure above.

Q: What is the mass number of a helium atom that has three neutrons?

A: The mass number is the number of protons plus the number of neutrons. For helium atoms with three neutrons, the mass number is 2 (protons) + 3 (neutrons) = 5.

Number?

Atomic Numbers 8

Q: How would you represent this isotope of helium to show its atomic number and mass number?

A: You would represent it by the element’s symbol and both numbers, with the mass number on top and the atomic number on the bottom: 5/2 He

Summary

  • Elements are pure substances that make up all matter, so each one is given a unique name. The names of elements are also represented by unique one-, two-, or three- letter symbols.
  • The number of protons in an atom is called its atomic number. This is also unique for each element.
  • An atom’s mass number is its mass in atomic mass units (amu), which is about equal to the total number of protons and neutrons in the atom. Different isotopes of an element have different mass numbers because they have different numbers of neutrons.

Explore More

Use the periodic table of the elements at the first URL below to fill in the blanks in the worksheet at the second URL.

Review

  1. What is the atomic number of an atom? Why is this number important?
  2. Describe the atomic mass unit. What does it represent and what does it equal?
  3. The symbol below represents an isotope of helium. How many protons and neutrons does it have?


  1. All carbon atoms have six protons. Most also have six neutrons, but some have seven or eight neutrons. What is the mass number of a carbon isotope that has seven neutrons?

Atomic Numbers Of Elements

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