Science Do as directed; [Che-1 M]

Atomic No. = 17
E.C. = (2, 8, 7)
Valency = 8 - no. of valence electrons
Valency = 8 - 7
Valency = 1

Atomic No: 18
Electronic configuration: (2, 8, 8)
The special thing about the outermost shell is that it is completely filled with the electrons.

Neutron is not present in ordinary hydrogen atom.

lodine-131 radioisotope is used to determine the activity of thyroid gland.

Nucleus was discovered by Rutherford in the alpha particle scattering experiment.

Proton is present in same fixed no. in the atoms of any particular element.

Deuterium, Protium and Tritium are isotopes.
Argon and Calcium are isobars.

Helium has less than 8 electrons in the valence shell of an atom. Its atomic no. is 2

Radioactive isotopes have unstable nuclei and emit various types of radiations.

Atoms containing same number of protons and electrons but different number of neutrons are called ISOTOPES.

The given pair are isotopes.

Isotopes.

Mass No. = Atomic no. + No. of neutrons

Due to slight difference in the masses of the isotopes of an element, the physical properties of the isotopes are slightly different.

Because all the isotopes of an element have identical atomic configuration containing same number of valence electrons, therefore, all the isotopes of an element show identical chemical properties.
For example: Cl^-₃₅ and Cl^-₃₇, show identical chemical properties as they have same no. of 7 valence electrons.

The difference in the masses of isotopes of an element is due to different number of neutrons in their nuclei.

Positive charge on the nucleus is due to presence of protons.

There are 3 valence electrons present in the element with atomic no. 13.
Valence shell of this atom is M.

Nucleus is a small positively charged part at the center of an atom. Nucleus is positively charged.

Maximum of 8e^- can be accommodated in outermost shell of an atom.

Maximum of 2e^- can be accommodated in innermost shell of an atom.

Maximum of 8e^- can be accommodated in L shell of an atom.

Maximum of 2e^- can be accommodated in K shell of an atom.

Maximum of 32e^- can be accommodated in N shell of an atom.

Maximum of 18e^- can be accommodated in M shell of an atom.

Noble gases.

Electronic configuration of hydrogen : 1

Absolute mass of proton 1.6 × 10^-27Kg
Absolute charge of proton 1.6 × 10^-19C

Absolute mass of electron is 9 × 10^-28Kg
Absolute charge on electron is 1.6 × 10^-19C

Protons are positively charged particle found in the atoms of all the elements whereas neutron is a neutral particle found in the nucleus of an atom.

The neutron is a neutral particle found in the nucleus of an atom. Its relative mass is 1u. It has no charge.

Atomic no. is characteristic for any particular element.

The conclusion is that all the atoms contain negatively charged particles called electrons.

The number of electrons present in the valence shell are called valence electrons.
Valence electrons are situated in the outermost shell.

K, L, M, N were the letters used by Bohr to represent electron shells in an atom.

Isobars are the atoms of different elements having different atomic numbers but the same mass number (or same atomic mass).

E.C of Nitrogen = 2, 5 So, no. of valence electrons in Nitrogen atom = 5

Here, A and D are isotopes as they have the same number of protons but different number of neutrons.

Atomic No. of X = 16
E.C. of X = (2, 8, 6)

Radioactive isotopes are used in the treatment of cancer.
One such isotope is Cobalt-60.

Radioactive isotopes are used in industry to detect the leakage in underground oil pipelines, gas pipelines and water pipes.

Three subatomic particles present in atom are electrons, protons and neutrons.

Rutherford discovered nucleus of an atom.