Worksheet 2.
4
Atomic structure
1
a Complete these sentences by deleting the incorrect word in each pair.
Atoms of the same element have the same number of protons / neutrons. The number of
protons / neutrons in an atom is called its proton / mass number. The number of protons
plus the number of electrons / neutrons in an atom gives the atomic / nucleon number. As
an atom is neutral, the number of negative electrons / neutrons in an atom is always the
same as the number of positive protons in the nucleus.
b Complete the following sentences using the words below to fill the gaps.
eight
electrons
closest
energy
shells
The ........................................ in an atom are not free to move where they like. They can only
occur at fixed distances from the nucleus in electron ........................................ (or
........................................ levels).
The first shell, ........................................ to the nucleus, can only take two electrons, while
the
second shell can take up to ........................................ electrons.
For each of these atoms of the following elements, give the proton number (atomic number) and
the nucleon number (mass number).
a
helium (He) has 2 protons, 2 neutrons and 2 electrons ........................
b fluorine (F) has 9 protons, 10 neutrons and 9 electrons ........................
c
iron (Fe) has 26 protons, 30 neutrons and 26 electrons ........................
d uranium (U) has 92 protons, 140 neutrons and 92 electrons ........................
Cambridge IGCSE Chemistry
Original material Cambridge University Press 2011
a Complete the table below to show the subatomic particles present in these atoms.
Element
Protons
Li
Neutrons
Electrons
Na
11
15
23
31
Pb
82
b Chlorine atoms come in two forms:
i
Nucleon
number
35
17
Cl and
37
17
207
Cl .
How do you know that they are both atoms of the same element?
...............................................................................................................................................
ii
What is the difference between the two types, or isotopes, of chlorine?
...............................................................................................................................................
iii
Which element is
12
6
14
7
14
6
X an isotope of?
Explain your answer.
...............................................................................................................................................
Diagrams A, B and C represent the atoms of three elements. Name the elements.
A......................................... B......................................... C.........................................
b These elements are all very unreactive gases. What can be said about the electron
arrangements of these atoms?
.....................................................................................................................................................
Cambridge IGCSE Chemistry
Original material Cambridge University Press 2011
Cambridge IGCSE Chemistry
Original material Cambridge University Press 2011
