Atomic structure and periodic classification Qns

1. What are valence electrons?
   Valence electrons are the electrons in the outermost shell (energy level) of an atom. They determine the chemical properties and bonding behavior of an element.
2. What is an ion?
   An ion is an atom or a group of atoms that has gained or lost electrons, resulting in a positive or negative charge.
3. What is an ionic bond?
   An ionic bond is a chemical bond formed between oppositely charged ions. It occurs when electrons are transferred from one atom to another.
4. What is a covalent bond?
   A covalent bond is a chemical bond formed by the sharing of electron pairs between atoms. It occurs between non-metal atoms.
5. What is electronegativity?
   Electronegativity is the tendency of an atom to attract electrons towards itself in a chemical bond.
6. What is the octet rule?
   The octet rule states that atoms tend to gain, lose, or share electrons in order to achieve a stable electron configuration with 8 valence electrons.
7. 1. Why isotopes have the same chemical properties?
      Because they have the same arrangement and number of electrons OR All isotopes of an element have the same number of valence electrons.
   2. Na and K are in group I in the periodic table and they have similar chemical properties. Briefly explain why?
      They have the same number of electrons, that is 1, in outermost shell. These outermost electrons are called valence electrons. Valence electrons determines the chemical properties of an atom.
8. What are the valence electrons present in the atom Y whose atomic number is 15. By using the electronic configuration state the group and period in which the atom Y occurs. Write the electronic configuration of an ion Y.
9. Why the relative atomic masses of most elements are not whole numbers?
   The relative atomic masses of most elements are not whole numbers due to the existence of isotopes. The relative atomic mass of an element is calculated as average of the masses of its isotopes. The more abundant isotopes contribute more to the average atomic mass.
10. The element chlorine is a mixture of two isotopes ³⁵₁₇Cl and ³⁷₁₇Cl.
    
    1. Why the two atoms have the same chemical properties?
    2. In what ways do the atoms of ³⁵₁₇Cl differ from the atoms of ³⁷₁₇Cl?
11. Why atoms are neutral? Why the nucleus of an atom is positively charged?
It is neutral because the number of protons equals to the number of electrons. Nucleus of an atom is positively charged because proton which is positively charged particle is present inside it.