8 th Science, 5.2, Inside the Atom, Notes. 

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What's app group 2

      Atomic structure

An atom is formed from the nucleus and the extranuclear part.

Atom contain three types of subatomic particles, Protons, electrons and neutrons. 

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        Nucleus

The atomic nucleus is positively (+ve) charged. 

Almost entire mass of the atom is concentrated in the nucleus.

 The nucleus contains two types of subatomic particles

together called nucleons. 

Protons and neutrons are the two types of nucleons.

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      Proton (p)

Proton is a positively charged subatomic particle in the atomic nucleus. 

The positive charge on the nucleus is due to the proton in it. 

A proton is represented by the symbol ‘p’. 

Each proton carries a positive charge of +1e. 

1e = 1.6  * 10^-19 coulomb. 

Atomic number (Z): The number of protons in the nucleus of an atom is the atomic number of that element and is denoted by the ‘Z’.

Mass of one proton is approximately 1u (1 Dalton)

1u = 1.66  * 10^-27 Kg. 

The mass of one hydrogen atom is also approximately 1 u.

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Neutron (n)

Neutron is an electrically neutral subatomic particle and is denoted by the symbol ‘n’. 

The number of neutron in the nucleus is denoted by the symbol ‘N’. 

Atomic nuclei of all the elements except hydrogen with atomic mass 1u, contain neutrons. The mass of a neutron is approximately 1 u.

The mass of a neutron is almost equal to that of a proton.(Mass of neutron is slightly heavier than proton i.e about 0.001389 amu)

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Extranuclear part

The extranuclear part in the atomic structure includes electrons revolving around the nucleus and the empty space in between the nucleus and the electron.

Electron (e-)

Electron is a negatively charged subatomic particle and is denoted by the symbol ‘e-’. 

Each electron carries one unit of negative charge (-1e). 

Mass of an electronis 1836 times less than that of a hydrogen atom. Therefore the mass of an electron can be treated as negligible.

Electron in the extranuclear part revolve in the discrete orbits around the nucleus. 

The orbits being three dimensional in nature, a term ‘shell’ is used in stead of the term ‘orbit’.

The energy of an elctron is determined by the shell in which it is present.

p = e.The number of electron in the extranuclear part is equal to the number of proton in the nucleus (Z). Therefore electrical charges are balanced and the atom is electrically neutral.

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How many types of subatomic particles

are found in atom?

Ans:- 

• Proton 
• Neutron 
• Electron

✿¸.•*¨`*•..¸✿🧿✿¸.•*¨`*•..¸✿

 🛞 Which subatomic particles are electrically charged?

Ans:- 

Proton and electron are electric recharged.

Proton is positively charged. 

Electron is negatively charged.

      ..•♡•:.:✦:.:•♡•..

☕. Which subatomic particles are present in the nucleus?

Ans:- 

Proton (p) and neutron (n) particles are present in the nucleus.

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🎺 Where are electrons revolving around the nucleus placed?

Ans:- Electron revolve around the nucleus in a specific shell.

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🪷 Mass number (A): The total number of protons and neutron in an atom is the atomic mass number of that element. The mass number is denoted by the symbol ‘A’.

A = p + N

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🌺 The symbol used for oxygen is ‘O’. There are 8 protons and 8 neutrons in its nucleus. From this determine the atomic number (Z) and mass number (A) of oxygen and arrange these in a conventional symbol.

Ans:- 

The atomic number (Z) :-  8.

Mass number (A) :- p + n

                                    = 8+8 

                                    = 16

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 🦅 Atomic number of carbon is 6. How many electrons are there in a carbon atom ?

Ans:- 

The number of electron in the extra nuclear part is equal to the number of proton in the nucleus (Z).

The number of protons in the nucleus of an atom is the atomic number of that element.

∴ p = e

∴ e = 6

 

*❀꧁❂꧂❀*

⚛️ A sodium atom contains 11 electrons. What is the atomic number of sodium ?

Ans:- 

The number of protons in the nucleus of an atom is the atomic number of that element.

The number of electron in the extra nuclear part is equal to the number of proton in the nucleus (Z)

∴ p (Z) = e 

∴ p (Z) =  11

  

*⋐⋑🔸⚜️ 🔸⋐⋑*

🌞 The atomic number and mass number of magnesium are 12 and 24 respectively. How will you show this by the convention symbol ?

Ans:- 

 𝄅𝄄𝄅𝄈⧗⃝✿*~> ~*✿⃝𝆭⧗⃪ ꯭𝄈𝄅𝄄𝄅🪈꯭

🔥 The atomic number and mass number of calcium are 20 and 40 respectively. Deduce the number of neutron present in the calcium nucleus.

Ans:- 

Atomic number (Z) - 20

 and 

Mass number (A) - 40 

∴ A = z + n

∴ n = A- Z

∴ n = 40 - 20 

∴ n  = 20

*།།◆️___🧿___◆️།།*

Some interesting fact. 

The atomic radius of sodium (Na) is  186 pm.

The size of a sodium nucleus is approximately 0.0227 picometers, which is about 1/10,000th the size of the entire sodium atom. 

1 pm =  10 ^− 12 m .

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