chemistry

1.what is meant by atomic number of an element?

2.the mass number of an element is 18,it contains 7 electrons.what is the number of protons and neutrons in it?what is the atomic number of the element?

3.an element has an atomic number of 11 and its mass number is 23?what is the arrangement of electrons in the shells? state nuclear composition of an atom of the element?

4.what is the atomic number of an element which has 7 electrons in the M shell?(the K and L shells are completely filled with electrons)?

5.an element has atomic number 13 and atomic mass of 27.(a)how many electrons are there in each atom of the element?(b)how are these electrons distributed in the various energy levels?

6.give the number of protons,neutrons and electrons per atom in the two isotopes of chlorine 17Cl^35 and 17cl^37?

7.what is the reason for the different atomic masses of the isotopes of an element?

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asked by pooja
  1. I will be happy to critique your thinking on these.

  2. Protons are7 and neutrons are11

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    posted by sonal
  3. 1.The atomic number is equal to the number of protons in an atom's nucleus. The atomic number determines which element an atom is.

    2. The number of protons and the number of neutrons determine an element's mass number.
    (Number of protons + number of neutrons) = mass number. 1 proton= 1 electron.
    18 (mass number) - 7 (number of electrons which is equal to the number of protons) = 11 (number of neutrons) .
    7 Protons tells us that this element is the 7th element in the periodic table which is Nitrogen.

    3. The 11th element in the periodic table is Sodium (Na). Sodium's mass number is technically 22.9898 amu but i guess they rounded it for simplicity.
    Sodium has 3 shells.
    The first shell (K) has 2 electrons (which for the first shell is complete meaning there are no valence electrons). The second shell (L) has 8 electrons (which for the second shell is complete).
    The third shell (M) has 1 electron (the third shell requires 8 electrons to be complete so this means that it has 7 valence electrons).
    A valence electron is an electron that is associated with an atom, and that can participate in the formation of a chemical bond; in a single covalent bond, both atoms in the bond contribute one valence electron in order to form a shared pair.

    4. The electron shells are labeled K, L, M, N, O, P, and Q; or 1, 2, 3, 4, 5, 6, and 7; going from innermost shell outwards.
    Since M is the third shell and it was stated that the K and L shells were completely filled we can add 2 (K) + 8 (L) + 7 (M) = 16 electrons.
    16 electrons = 16 protons.
    The atomic number is 16.
    The 16th element in the periodic table is Sulphur(UK Spelling) or Sulfur (US Spelling)

    5.The 13th element in the periodic table is Aluminium which technically has an atomic mass of 26.9815386 amu. Because the atomic number is 13 we know that the number of protons is 13 which means that the number of electrons is 13. Using the K,L,M shells we can determine that Aluminium has completely filled K and L shells and has 3 electrons in the M shell. (13-(2(K shell)+8(L shell))=3

    6. An isotope is any of two or more forms of a chemical element, having the same number of protons in the nucleus, or the same atomic number, but having different numbers of neutrons in the nucleus, or different atomic weights.
    Number of neutrons = (atomic mass - number of protons)

    7. The more neutrons an element has the bigger the atomic mass.

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    posted by Chelsea

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