SC3 Atomic Structure

Question 1

SC3a
1) What was Dalton’s view about atoms?
2) Describe how the subatomic particles are arranged in an atom
3) Explain how atoms of different elements are different

Answer 1

1) John Dalton stated that atoms were tiny hard spheres that could not be broken down.
2) The protons and neutrons are found in the nucleus. The nucleus has a positive charge. The electrons are found on the outer shells.
3) Atoms of different elements have a different number of protons, neutrons, and electrons.

Question 2

SC3a
1) Recall the charges and relative masses of the three subatomic particles
2) Explain why all atoms have no overall charge
3) Describe how the size of an atom compares to the size of its nucleus

Answer 2

1) Charges: Proton +1, Neutron 0, Electron -1. Protons and neutrons have a relative mass of 1, and electrons have a relative mass of almost 0.
2) Protons have a relative charge of +1, and electrons have a relative charge of -1. Because there is an equal number of protons and electrons in an atom, the positive charges on the protons cancel out the negative charges on the electrons.
3) The size of an atom is very large compared to the size of its nucleus. Therefore, most of an atom is empty space

Question 3

SC3b
1) State where most of the mass of an atom is found
2) State the meaning of atomic number
3) State the meaning of mass number
4) Describe how the atoms of the same elements and different elements can vary

Answer 3

1) Most of the mass of an atom is found in the nucleus.
2) The number of protons in an atom of an element is its atomic number.
3) The mass number of an atom is its total number of protons and neutrons.
4) Atoms of an element have identical numbers of protons and electrons, but can have different numbers of neutrons. atoms of different elements have different numbers of protons and electrons.

Question 4

SC3c
1) State what is meant by an isotope
2) How do you find the numbers of protons, neutrons and electrons using atomic numbers and mass numbers
3) Explain why the relative atomic mass of many elements is not a whole number

Answer 4

1) An isotope is atoms of an element with the same number of protons (atomic number) but a different mass number due to a different amount of neutrons.
2) - Number of protons = atomic number.
- Number of electrons = atomic number.
- Number of neutrons = mass number - atomic number.
- The mass number is the larger number
3) The atomic masses of most elements are not whole numbers, because they are an average of the mass numbers of the different isotopes of that element, depending on the percentage of how many there are of each.

Question 5

SC3c
1) How do you calculate the relative atomic mass of an element from the relative masses and abundances of its isotopes?
2) What is relative atomic mass?

Answer 5

1) An example is chlorine. Chlorine naturally exists as two isotopes, (chlorine-35) and (chlorine-37). The abundances (overall proportions) of chlorine-35 is 75% and the abundance of chlorine-37 is 25%. The formula is: total mass of atoms/ number of atoms. We use 100 as the number of atoms. Therefore: ((35 * 75) + (37 * 25)) / 100 = 35.5 .
2) The relative atomic mass of an element is the average mass of one atom of the element, compared to 1/12th of the mass of atom of carbon-12.