The Atomic Number Of An Atom Is The Number Of

What Are Atomic Number and Atomic Weight?

• The Atomic Number Of An Atom Is The Number Of Its
• The Atomic Number Of An Atom Is The Number Of Neutrons

What is an element?

Chemical behavior is what originally led scientists to classify matter into various elements

If an oxygen atom has 8 protons in its nucleus, what is its atomic number? 8 If a substance cannot be broken down chemically into a simpler substance, it is. The atomic number is located above the element symbol, in the upper left-hand corner of the square. The atomic number will tell you how many protons make up a single atom of an element. For example, boron (B) has an atomic number of 5, therefore it has 5 protons.

. Chemical behavior is the ability of an atom to combine with other atoms. In more technical terms, chemical behavior depends upon the type and number of the chemical bonds an atom can form with other atoms. In classroom kits for building models of molecules, atoms are usually represented by colored spheres with small holes for pegs and the

The Atomic Number Of An Atom Is The Number Of Its

bonds are represented by the small pegs that can connect the spheres. The number of peg holes signifies the maximum number of bonds an atom can form; different types of bonds may be represented by different types of pegs. Atoms that have the same number of peg holes may have similar chemical behavior. Thus, atoms that have identical chemical behavior are regarded as atoms of the same element. For example, an atom is labeled a 'carbon atom' if it can form the same number, types, and configurations of bonds as other carbon atoms. Although the basics are simple to explain, how atoms bind to each other becomes very complex when studied in detail; new discoveries are still being made as new types of materials are formed.

What is atomic number?

An atom may be visualized as a miniature solar system, with a large central nucleus orbited by small electrons. The bonding capacity of an atom is determined by the electrons. For example, atoms that in their normal state have one electron are hydrogen atoms and will readily (and sometimes violently) bond with oxygen. This bonding capacity of hydrogen was the cause of the explosion of the airship Hindenburg in 1937. Atoms that in their normal state have two electrons are helium atoms, which will not bond with oxygen and would have been a better choice for filling the Hindenburg.

We can pursue the question back one step further: What determines the number of electrons? The number of protons in the nucleus of the atom. Here, the analogy between an atom and the solar system breaks down. The force that holds the planets in their orbits is the gravitational attraction between the planets and the sun. However, in an atom what holds the electrons in their orbit is the electrical attraction between the electrons and the protons in the nucleus. The basic rule is that like charges repel and opposite charges attract. Although a proton has more mass than an electron, they both have the same amount of electrical charge, but opposite in kind. Scientists have designated electrons as having a negative charge and protons as having a positive charge. One positive proton can hold one negative electron in orbit. Thus, an atom with one proton in its nucleus normally will have one electron in orbit (and be labeled a hydrogen atom); an atom with ninety-four protons in its nucleus will normally have ninety-four electrons orbiting it (and be labeled a plutonium atom).

The number of protons in a nucleus is called the atomic number and always equals the number of electrons in orbit about that nucleus (in a nonionized atom). Thus, all atoms that have the same number of protons--the atomic number--are atoms of the same element.

What is atomic weight?

The nuclei of atoms also contain neutrons, which help hold the nucleus together. A neutron has no electrical charge and is slightly more massive than a proton. Because a neutron can decay into a proton plus an electron (the essence of beta decay), it is sometimes helpful to think of a neutron as an electron and a proton blended together, although this is at best an oversimplification. Because a neutron has no charge,

a neutron has no effect on the number of electrons orbiting the nucleus. However, because it is even more massive than a proton, a neutron can add significantly to the weight of an atom. The total weight of an atom is called the atomic weight. It is approximately equal to the number of protons and neutrons, with a little extra added by the electrons. The stability of the nucleus, and hence the atom's radioactivity, is heavily dependent upon the number of neutrons it contains.

What notations are used to represent atomic number and weight?

Each atom, therefore, can be assigned both an atomic number (the number of protons equals the number of electrons) and an atomic weight (approximately equaling the number of protons plus the number of neutrons). A normal helium atom, for example, has two protons and two neutrons in its nucleus, with two electrons in orbit. Its chemical behavior is determined by the atomic number 2 (the number of protons),

The Atomic Number Of An Atom Is The Number Of Neutrons

which equals the normal number of electrons; the stability of its nucleus (that is, its radioactivity) varies with its atomic weight (approximately equal to the number of protons and neutrons). The most well-known form of plutonium, for example, has an atomic number of 94, since it has 94 protons, and with the 145 neutrons in its nucleus, an atomic weight of 239 (94 protons plus 145 neutrons). In World War II, its very existence was highly classified. A code number was developed: the last digit of the atomic number (94) and the last digit of the atomic weight (239). Thus, in some of the early documents examined by the Advisory Committee, the term 49 refers to plutonium.

Styles of notation vary, but usually isotopes are written as:

_{atomic number} Chemical abbreviation ^{atomic weight}

or as

^{atomic weight} Chemical abbreviation

Thus, the isotope of plutonium just discussed would be written as:

₉₄Pu239

or as

²³⁹Pu

Since the atomic weight is what is often the only item of interest, it might also be written simply as Pu-239, plutonium 239, or Pu²³⁹.

02nd Jul 2019 @ 15 min read

An atom comprises electrons, protons, and neutrons. Electrons revolve around the nucleus of an atom just like the Earth around the Sun. Protons and neutrons reside in the centre of an atom called nucleus. Electrons are negatively charged while protons are positively charged. Neutrons are neutral i.e., no charge. In an unbounded stable atom, the number of protons equals the number of electrons. This makes the net charge of an atom zero. These number of protons are unique for a given element, and the number is called the atomic number or proton number.

Definition of Atomic Number

The Gold Book of the International Union of Pure and Applied Chemistry (IUPAC) defines an atomic number as 'the number of protons in an atomic nucleus.'

Symbol

The symbol used for the atomic number is Z.

Representation

The atomic number is subscripted to the left of the symbol of an element. Consider an example of calcium, which has the atomic number of 20 (Z = 20). So, number 20 is subscripted to the symbol Ca i.e., ₂₀Ca.

Note: While the atomic number is subscripted, the mass number of an element is superscripted (see below figure). Winamp skins 2020.

Atomic Number vs Mass Number

As discussed, the atomic number is the number of protons presents in the nucleus while the mass number is the number of nucleons (protons and neutrons) presents in the nucleus of an atom. This both numbers are different by the definition itself. The below table highlights some of the key differences between the two numbers.

Table 1: Difference between Atomic Number and Mass Number

Atomic Number	Mass Number
The atomic number is the number of protons present in the nucleus of an atom.	The mass number is the number of nucleons (protons and neutrons) present in the nucleus of an atom.
It is denoted as Z.	It is denoted as A.
It is always fixed for a given element, for example, the atomic number of an oxygen atom is 16. This is true for any oxygen atom in the universe.	It can be different for a given element, for example, an oxygen atom can have a mass number of 16, 17, or 18.
Two different elements always have a different atomic number as in 40 20Ca and 40 18Ar.	Two different elements can have the same mass number as in 40 20Ca and 40 18Ar.
It is always a whole number.	It is also always a whole number.
It is always smaller than the mass number (except in the case of 1 1H where both are equal). In fact, the atomic number is a subset of mass number.	It is always larger than the atomic number (except in the case of 1 1H where both are equal).

Relation with Mass Number and Neutron Number

The atomic number (Z) is related to the mass number (A) and the neutron number (N) by the following equation.

Atomic Number and Atomic Weight

The atomic weight or the relative atomic mass is the ratio of the average atomic mass of an atom to some reference standard. If the reference standard is considered 1 u, the atomic weight is the ratio of the average atomic mass to one unified mass unit (1 u). In other words, it is the numeric value of the average atomic mass. It is a dimensionless quantity. For lighter elements, the atomic weight almost twice the atomic number (see below figure). But for heavier elements, the atomic weight exceeds the twice of the atomic number. This is due to an increase in the neutron number compare to the proton number.

Atomic Number and Chemical Properties

The chemical properties of an atom are determined by the number of electrons particularly the number of electrons present in the outermost shell. For an uncharged, unbounded atom, the number of electrons always equals the number of protons. Thus, the atomic number decides the chemical nature of an atom.

Atomic Number and Isotopes

Isotopes are the atoms of the same elements, but with a different mass number. The atomic number can be used to distinguished the isotopes of an element. This is because isotopes of a given element have the same number of protons; they only differ in the number of neutrons. Instead, the mass number, which incorporates the neutron number, is used to identify the isotopes. Consider an example of oxygen. The common isotopes of oxygen are ¹⁶
₈O, ¹⁷
₈O, and ¹⁸
₈O. All these isotopes have the atomic number of 8; they only differ in the mass number.

List of Elements by Atomic Number

The below table lists all 118 elements by atomic number.

Table 2: List of Elements by Atomic Number

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

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'Atomic Number' ChemistryGod, 02nd Jul 2019, https://chemistrygod.com/atomic-number/