electron cloud nucleus consisting of protons and neutrons
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Electron cloud
Nucleus consisting of protons and neutrons
Electron: It carries a negative charge. It has a mass only about 1/1850 of the proton.
Nucleus consisting of protons and neutrons
Electron cloud
It is orbiting the nucleus at high speeds.
Proton: It is found in the nucleus .
It carries a positive charge.
Neutron: It does not carry any charge.
It has about the same mass as a proton.
Nucleus consisting of protons and neutrons
Electron cloud
Atoms of different elements have different number of protons, electrons and neutrons.
Example:
AtomNo. of
electronNo. ofproton
No. ofneutrons
Carbon 6 6 6
Nitrogen 7 7 7
Fluorine 9 9 10
Atom No. ofproton
Atomicnumber
Hydrogen 1 1
Oxygen 8 8
Calcium 20 20
The atomic number is the number of protons in an atom.
Mass number: It is the total number of protons and neutrons in
the nucleus of an atom.
AtomNo. ofproton
No. ofneutron
Mass no.
Carbon 6 6 12
Nitrogen 7 7 14
Fluorine 9 10 19
Atom No. ofproton
No. ofelectrons
Hydrogen 1 1
Oxygen 8 8
Calcium 20 20
For any neutral atom, the number of electrons is equal to the number of protons.
Data for atoms of the first 20 elementsAtom
Atomicnumber
No. ofelectrons
No. ofprotons
No. ofneutrons
Massnumber
H 1 1 1 0 1He 2 2 2 2 4Li 3 3 3 4 7Be 4 4 4 5 9B 5 5 5 6 11C 6 6 6 6 12N 7 7 7 7 4O 8 8 8 8 16F 9 9 9 10 19
Ne 10 10 10 10 20Na 11 11 11 12 23Mg 12 12 12 12 24Al 13 13 13 14 27Si 14 14 14 14 28P 15 15 15 16 31S 16 16 16 16 32Cl 17 17 17 18 35Ar 18 18 18 18 36K 19 19 19 20 39Ca 20 20 20 20 40
Draw a labelled diagram to show the structure of an atom.
Nucleus consisting of protons and neutrons
Electron cloud
What is the charge of electron?
What is the charge of proton?
Compare the mass of electron and that of proton.
Describe the movement of electron in an atom.
Electron: It carries a negative charge.
It carries a positive charge.
It is orbiting the nucleus at high speeds.
Electron has a mass only about 1/1850 of the proton.
What is the charge of a neutron?
Compare the mass of neutron and that of proton.
Neutron: It does not carry any charge.
They have about the same mass.
The atomic number is the number of protons in an atom.
How do you know atomic number of an atom from the number of protons?
1. Complete the following table.
Name ofatom
SymbolAtomic
no.No. ofproton
No. ofelectrons
Potassium 19
Carbon 6
Nitrogen 7
Argon 18
iron 26
Suggested Answers
Name ofatom
SymbolAtomic
no.No. ofproton
No. ofelectrons
Potassium K 19 19 19
Carbon C 6 6 6
Nitrogen N 7 7 7
Argon Ar 18 18 18
iron Fe 26 26 26
2. Complete the following table for three element A, B and C
ElementAtomic
no.Mass no.
No. ofneutrons
No. ofelectrons
A 12 6
B 19 39
C 27 13
Suggested Answers
ElementAtomic
no.Mass no.
No. ofneutrons
No. ofelectrons
A 6 12 6 6
B 19 39 20 19
C 13 27 14 13
3. Complete the following table.
No. ofneutrons
No. ofprotons
No. ofelectrons
Mass no.
26 22
74 127
34 79
82 207
20 39
Suggested answers
No. ofneutrons
No. ofprotons
No. ofelectrons
Mass no.
26 22 22 48
74 53 53 127
45 34 34 79
125 82 82 207
19 20 20 39
It is the distribution of electrons in the various shells of an atom.
1st shell (energy level)
4th shell (energy level)
3rd shell
2nd shell
nucleus
nucleus
Energy of the electron in the first shell is lower
nucleus
Energy of the electron in the third shell is higher
The first shell can hold a maximum of 2 electrons
The second shell can hold a maximum of 8 electrons
The third shell can hold a maximum of 18 electrons
The following rules can be applied to find out the electronic configuration of an atom.
The first 2 electrons go into the first shell and complete it.
The next 8 electrons go into the second shell and complete it.
The next 8 electrons go into the third shell.
The next 2 electrons go into the fourth shell.
The next 10 electrons go into the third shell and complete it.
Electron diagrams also show the distribution of electrons in atoms.
E.C.: 1
For example, hydrogen atom
E.C. : 2, 1
Lithium atom, atomic no. = 3
Sodium atom, atomic no. = 11
E.C. : 2, 8, 1
E.C. :
2, 8, 8, 2
Calcium atom, atomic no. = 20
Beryllium atom
E.C. : 2, 2
Work out electronic configuration and electron diagram for beryllium, atomic no.=4
E.C. : 2, 7
Work out electronic configuration and electron diagram for fluorine atom, atomic no.=9
Work out electronic configuration and electron diagram for aluminium, atomic no.=13
E.C.: 2, 8, 3
Potassium atom, atomic no. = 19
E.C.: 2, 8, 8, 1
He42
atomic number
mass number
Cl3517
atomic number
mass number
XAZatomic number
mass number
3.5 Isotopes
Isotopes are atoms of a particular element with the same number of protons and electrons but a different number of neutrons.
Three isotopes of hydrogen.
1
1H
2
1H
3
1H
3.5 Isotopes
Isotopes of an elements have the same number of electrons, therefore the same electronic configuration.
Two isotopes of chlorine
35
17Cl
37
17Cl
They have different mass numbers.
Which of the following are isotopes of the same element? Explain.
Atoms A B C D E
No. of neutrons 35 45 37 44 35
No. of protons 45 35 45 35 44
No. of electrons 45 35 45 35 44
Mass number 80 80 82 79 79
A, C are isotopes of an element.B, D are isotopes of another element.
Atoms A and atom C have the same number of protons but of different number of neutrons.