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Q1. Neutrons are present in the nucleus of all atoms except:
Neutrons are present in the nucleus of all atoms except hydrogen. The most common isotope of hydrogen (protium) has no neutrons in its nucleus—it contains only one proton. Other isotopes of hydrogen (deuterium and tritium) contain neutrons, but the typical hydrogen atom does not.
Q2. Fluorine has 7 electrons in outermost shell. Its valency is:
Fluorine has 7 electrons in its outermost shell and needs 1 more electron to complete its octet (8 electrons). Therefore, its valency is 1 (it can accept one electron). This makes fluorine a highly reactive non-metal.
Q3. Elements with full outermost shell are called:
Elements with a full outermost shell are called inert elements (or noble gases). They have 8 electrons in their outermost shell (except helium, which has 2) and are chemically stable. They do not easily gain, lose, or share electrons because they already have a stable configuration.
Q4. Sulphur outermost electrons:
Sulphur has 6 electrons in its outermost shell. It has atomic number 16 with electron distribution 2, 8, 6. Sulphur needs 2 more electrons to complete its octet, giving it a valency of 2. It is a non-metal that forms compounds like H₂S and SO₂.
Q5. A neutron is represented by the symbol:
A neutron is represented by the symbol ‘n’ (or sometimes n⁰ to indicate its neutral charge). Protons are represented by p⁺, electrons by e⁻, and alpha particles by α. The neutron was discovered by James Chadwick in 1932.
Q6. Fluorine outermost electrons:
Fluorine has 7 electrons in its outermost shell. With atomic number 9, its electron distribution is 2, 7. It is one electron short of a stable octet, making it highly reactive and giving it a valency of 1.
Q7. Neon has how many electrons in outermost shell?
Neon has 8 electrons in its outermost shell. Neon has atomic number 10 with electron distribution 2, 8. It has a complete octet, making it a noble gas with very low chemical reactivity. It does not form compounds easily.
Q8. Oxygen has how many electrons in outermost shell?
Oxygen has 6 electrons in its outermost shell. With atomic number 8, its electron distribution is 2, 6. Oxygen needs 2 more electrons to complete its octet, giving it a valency of 2. This is why water is H₂O—two hydrogen atoms share their electrons with one oxygen atom.
Q9. Maximum electrons in K-shell (n=1) is:
The maximum number of electrons in the K-shell (n=1) is 2. This is given by the formula 2n², where n=1 gives 2 × 1² = 2. Hydrogen and helium are the only elements with electrons in the K-shell. The K-shell is the innermost shell closest to the nucleus.
Q10. Electrons in the outermost shell are called:
Electrons in the outermost shell are called valence electrons. These electrons are the ones involved in chemical bonding. The number of valence electrons determines an element’s valency and chemical properties. For example, oxygen has 6 valence electrons, and its valency is 2.
Q11. Lithium outermost electron count is:
Lithium has 1 electron in its outermost shell. With atomic number 3, its electron distribution is 2, 1. Lithium is a metal that loses its single valence electron to achieve a stable configuration, giving it a valency of 1.
Q12. Hydrogen, lithium, and sodium have valency of:
Hydrogen, lithium, and sodium all have a valency of 1. Hydrogen needs 1 electron to complete its K-shell (duplet), while lithium and sodium have 1 electron in their outermost shell and need to lose it to achieve a stable configuration. This is why they are in Group 1 of the periodic table.
Q13. Maximum electrons in outermost shell is:
The maximum number of electrons in the outermost shell is 8 (except for the first shell, which has a maximum of 2). This is known as the octet rule. Atoms strive to have 8 electrons in their outermost shell to achieve stability, like noble gases.
Q14. Aluminium has electron distribution:
Aluminium has electron distribution 2, 8, 3. Aluminium has atomic number 13: 2 electrons in the K-shell, 8 in the L-shell, and 3 in the M-shell. It has 3 valence electrons, giving it a valency of 3.
Q15. Aluminium has valency of:
Aluminium has a valency of 3. It has 3 electrons in its outermost shell and tends to lose them to achieve a stable configuration like neon (2, 8). This makes aluminium a trivalent cation (Al³⁺) in its compounds.
Q16. Boron outermost electrons:
Boron has 3 electrons in its outermost shell. With atomic number 5, its electron distribution is 2, 3. Boron has 3 valence electrons and can form compounds by sharing these electrons, giving it a valency of 3.
Q17. The mass of an atom is the sum of:
The mass of an atom is the sum of protons and neutrons. Both protons and neutrons have approximately the same mass (about 1 u each). Electrons have negligible mass (about 1/1836 of a proton). Therefore, almost all the mass of an atom is concentrated in the nucleus.
Q18. Sharing, gaining or losing electrons determines:
Sharing, gaining, or losing electrons determines an element’s valency. Valency is the combining capacity of an atom, which depends on the number of electrons it needs to gain, lose, or share to achieve a stable electronic configuration.
Q19. Valence electrons determine:
Valence electrons determine the valency and chemical combining capacity of an element. The number of electrons in the outermost shell decides whether an element will gain, lose, or share electrons to form bonds. This determines how an element reacts with others.
Q20. Inert elements have valency of:
Inert elements (noble gases) have a valency of 0 because they already have a complete outermost shell (8 electrons, except helium with 2). They do not need to gain, lose, or share electrons to achieve stability, so they are chemically unreactive.
Q21. Which sub-atomic particle is present in the nucleus according to Rutherford?
According to Rutherford’s nuclear model, the nucleus contains protons. He discovered that the positive charge of an atom is concentrated in a tiny nucleus. Later, Chadwick discovered that neutrons are also present in the nucleus. Rutherford’s gold foil experiment established the existence of the proton.
Q22. Atomic number of Carbon is:
The atomic number of carbon is 6. This means carbon has 6 protons in its nucleus and 6 electrons in a neutral atom. Its electron distribution is 2, 4, giving it 4 valence electrons. Carbon is a non-metal that forms the basis of all organic chemistry.
Q23. Nitrogen has how many electrons in outermost shell?
Nitrogen has 5 electrons in its outermost shell. With atomic number 7, its electron distribution is 2, 5. Nitrogen needs 3 more electrons to complete its octet, giving it a valency of 3. It forms compounds like ammonia (NH₃) and nitrogen gas (N₂).
Q24. Beryllium outermost electrons:
Beryllium has 2 electrons in its outermost shell. With atomic number 4, its electron distribution is 2, 2. Beryllium is an alkaline earth metal that loses its 2 valence electrons to form Be²⁺ ions, giving it a valency of 2.
Q25. Atoms combine to achieve:
Atoms combine to achieve a fully-filled outermost shell (octet). This is the octet rule, which states that atoms tend to gain, lose, or share electrons to have 8 electrons in their outermost shell (or 2 for hydrogen and helium) to achieve a stable electronic configuration.
Q26. Chadwick discovered which sub-atomic particle in 1932?
James Chadwick discovered the neutron in 1932. He bombarded beryllium with α-particles and observed a neutral radiation that was later identified as neutrons. This discovery completed the picture of the atomic nucleus, which contains protons and neutrons.
Q27. Maximum electrons in N-shell (n=4) is:
The maximum number of electrons in the N-shell (n=4) is 32. This is given by the formula 2n²: 2 × 4² = 2 × 16 = 32. The N-shell is the fourth shell from the nucleus and can hold up to 32 electrons in a filled atom.
Q28. Phosphorus outermost electrons:
Phosphorus has 5 electrons in its outermost shell. With atomic number 15, its electron distribution is 2, 8, 5. Phosphorus needs 3 more electrons to complete its octet, giving it a valency of 3. It is a non-metal found in many biological molecules.
Q29. The outermost shell having 8 electrons is called:
The outermost shell having 8 electrons is called an octet. An octet represents a stable electronic configuration, which is why elements tend to achieve 8 electrons in their valence shell. Helium is an exception with a duplet (2 electrons). The octet rule is fundamental to understanding chemical bonding.
Q30. Most elements other than helium have how many electrons in outermost shell to be stable?
Most elements other than helium have 8 electrons in their outermost shell to be stable. This is called the octet rule. Noble gases have 8 valence electrons and are chemically inert. Hydrogen and helium are exceptions—they are stable with 2 electrons (duplet).
Q31. Neutrons have:
Neutrons have no charge (they are neutral). They are called “neutrons” because they are electrically neutral. They have the same mass as protons (about 1 u) but carry no electrical charge, which helps bind protons together in the nucleus.
Q32. Maximum electrons in L-shell (n=2) is:
The maximum number of electrons in the L-shell (n=2) is 8. Using the formula 2n²: 2 × 2² = 2 × 4 = 8. The L-shell is the second shell from the nucleus and can hold up to 8 electrons in a filled atom.
Q33. The energy levels or shells in an atom are represented by letters:
The energy levels or shells in an atom are represented by letters K, L, M, N, O, P, Q. The K-shell is the innermost shell (n=1), followed by L (n=2), M (n=3), N (n=4), and so on. These letters help identify different energy levels in an atom.
Q34. The first 18 elements follow:
The first 18 elements follow both the 2n² rule for inner shells and the rule that the outermost shell can have at most 8 electrons. For example, sodium (11 electrons) has distribution 2, 8, 1—the K-shell (n=1) has 2, L-shell (n=2) has 8, and M-shell has 1.
Q35. Atoms with fully filled outermost shell show:
Atoms with a fully filled outermost shell (like noble gases) show low chemical activity. They are chemically inert because they already have a stable configuration and do not need to gain, lose, or share electrons. This makes them unreactive.
Q36. Magnesium has how many electrons in K, L, M shells?
Magnesium has electron distribution 2, 8, 2. Magnesium has atomic number 12: 2 electrons in the K-shell, 8 in the L-shell, and 2 in the M-shell. It has 2 valence electrons, giving it a valency of 2.
Q37. Sodium has how many electrons in K, L, M shells?
Sodium has electron distribution 2, 8, 1. Sodium has atomic number 11: 2 electrons in the K-shell, 8 in the L-shell, and 1 in the M-shell. It has 1 valence electron, giving it a valency of 1.
Q38. Argon outermost electrons:
Argon has 8 electrons in its outermost shell. Argon has atomic number 18 with electron distribution 2, 8, 8. It has a complete octet, making it a noble gas with very low reactivity and a valency of 0.
Q39. Magnesium has valency of:
Magnesium has a valency of 2. It has 2 electrons in its outermost shell (M-shell) and tends to lose them to achieve a stable configuration like neon (2, 8). This makes magnesium a divalent cation (Mg²⁺) in its compounds.
Q40. Helium atom has atomic mass 4 u and 2 protons. Number of neutrons is:
Helium has atomic mass 4 u and 2 protons. The number of neutrons is atomic mass – atomic number = 4 – 2 = 2. Helium has 2 protons, 2 neutrons, and 2 electrons. This is the most common isotope of helium.
Q41. Helium atomic number is:
Helium has atomic number 2. This means helium has 2 protons in its nucleus and 2 electrons in a neutral atom. Its electron distribution is 2 (K-shell is full). Helium is a noble gas with a stable duplet configuration.
Q42. Maximum number of electrons in a shell is given by formula:
The maximum number of electrons in a shell is given by the formula 2n², where n is the principal quantum number (shell number). For example, for n=1 (K-shell), maximum electrons = 2 × 1² = 2. For n=2 (L-shell), maximum = 2 × 2² = 8.
Q43. Hydrogen atomic number is:
Hydrogen has atomic number 1. This means hydrogen has 1 proton in its nucleus and 1 electron in a neutral atom. Hydrogen is the simplest and lightest element with the electron distribution 1. It has valency 1.
Q44. Silicon outermost electrons:
Silicon has 4 electrons in its outermost shell. With atomic number 14, its electron distribution is 2, 8, 4. Silicon has 4 valence electrons and can share them to form compounds like SiO₂. It is a metalloid and a semiconductor.
Q45. Helium has how many electrons in outermost shell?
Helium has 2 electrons in its outermost (and only) shell. Helium has atomic number 2 with electron distribution 2. It has a full duplet, making it stable and chemically inert. Unlike other noble gases, it is stable with 2 electrons rather than 8.
Q46. Carbon has how many electrons in K and L shells?
Carbon has 2 electrons in the K-shell and 4 electrons in the L-shell. Carbon has atomic number 6 with electron distribution 2, 4. The K-shell has 2 electrons and the L-shell (outermost) has 4 valence electrons, giving carbon a valency of 4.
Q47. Electrons are not placed in a shell unless:
Electrons are not placed in a shell unless the inner shells are filled first. Electrons fill shells in order of increasing energy: K-shell first (n=1), then L-shell (n=2), M-shell (n=3), and so on. This is known as the Aufbau principle.
Q48. Maximum electrons in M-shell (n=3) is:
The maximum number of electrons in the M-shell (n=3) is 18. Using the formula 2n²: 2 × 3² = 2 × 9 = 18. The M-shell is the third shell from the nucleus and can hold up to 18 electrons in a filled atom.
Q49. Chlorine outermost electrons:
Chlorine has 7 electrons in its outermost shell. With atomic number 17, its electron distribution is 2, 8, 7. Chlorine needs 1 more electron to complete its octet, giving it a valency of 1. It is a non-metal that forms Cl⁻ ions.
Q50. The energy levels or shells in an atom can also be represented by numbers:
The energy levels or shells in an atom can be represented by numbers n=1, 2, 3, 4…, where n is the principal quantum number. n=1 is the K-shell (innermost), n=2 is the L-shell, n=3 is the M-shell, and n=4 is the N-shell. This numbering system is used in the formula 2n² for determining the maximum number of electrons in each shell.