JSSS
Student
Describe the structure of the atom, state the location, relative charge, and
atomic mass of the sub-atomic particles, and define atomic number and
isotope. Draw the Bohr structure of the first twenty elements. OC39
Student worksheet 1
According to the atomic theory elements are made up of extremely small particles called
ATOMS.
Up to May 2005 one hundred and fourteen different ELEMENTS have been discovered.
In an element all the atoms are similar to each other. They differ from to atoms of any other
element.
Carbon is an element.
1. What does this tell you about a piece of carbon? ________________________________
_____________________________________________________________________________
Magnesium, oxygen and hydrogen are also elements.
2. What can you say about the atoms of magnesium, oxygen and hydrogen? ____________
_____________________________________________________________________________
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JSSS
Student
In the Periodic Table the symbol for each element is given underneath its name e.g. the symbol
for neon is Ne
3. What is the symbol for aluminium? __________________________________________
4. What is the symbol for sulfur? ______________________________________________
5. What is the symbol for sodium? _____________________________________________
Subatomic particles
Atoms are made up of three types of smaller particles called subatomic particles. These smaller
particles are called protons, neutrons and electrons.
Mass of subatomic particles
A proton has a mass of 1 unit (or 1.67x10-24 grams)
A neutron also has a mass of about 1 unit
An electron has a mass of about 1/1850 unit
6. Which of the three subatomic particles is the lightest? ____________________________
Electric charge of subatomic particles
A proton has a positive electric charge (+1 unit)
A neutron has no electric charge (0)
An electron has a negative electric charge (-1 unit)
Location in the atom of the subatomic particles
The subatomic particles are arranged in a similar way in every atom.
The protons are found in the centre (nucleus) of the atom.
The neutrons are also found in the nucleus of the atom.
The electrons move around the nucleus of the atom.
7. Complete the table below.
Subatomic particle
Mass
Charge
Location
Proton
Electron
Neutron
Note
In all atoms the protons and neutrons are found in the nucleus, and the electrons
are found on the outside. Because the number of protons is always equal to the
number of electrons, an atom has no overall charge.
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JSSS
Student
From your study of static electricity, you should be able to answer the questions below about
how electric charges affect each other.
8. What effect do protons have on each other? ___________________________________
9. What effect do electrons have on each other? __________________________________
10. What effect do an electron and a proton have on each other? _______________________
In an atom the electrons arrange themselves in special ways. They move around the nucleus
within SHELLS which are definite distances from the nucleus. The inside shell can only hold
two electrons. There cannot be more than eight electrons in the second shell. The third shell can
also hold eight electrons. The electrons cannot go into the second shell until the first shell is full
and so on.
The electrons in the first twenty elements of the Periodic table go into the shells in the following
order 2,8,8,2.
In a HYDROGEN atom, the particles are arranged as shown in the diagram.
The subatomic particles in a CARBON atom are arranged as shown in the diagram.
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JSSS
Student
Here is a diagram of an OXYGEN atom.
Look at the diagrams of hydrogen, carbon and oxygen atoms. In each of these diagrams, the
smaller black circles represent the electrons, the larger black circles represent the protons, while
the neutrons are represented by the hollow circles. Fill in a table, like the one shown below, into
your notebook.
Atom
Number Of Protons
Number Of Electrons
Hydrogen
Carbon
Oxygen
11. What do you notice about the number of protons and the number of electrons in each of
these types of atoms?
__________________________________________________________________________
Atomic Number
The atomic number of an element gives the number of protons in an atom of that element. The
number of electrons in an atom is the same as the number of protons.
12. What is the atomic number of carbon? ________________________________________
13. How many protons are in the carbon atom? ____________________________________
14. How many electrons are in the carbon atom? __________________________________
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JSSS
Student
Electron Arrangement
A diagram of an atom showing how the electrons are arranged is called the Bohr structure of the
atom. The Bohr structure of the carbon atom is shown in the diagram. The electron arrangement
for the carbon atom is 2,4.
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JSSS
Student
15. What is the electron arrangement for an atom of sodium?
_____________________________________________________________________________
16. Draw the Bohr structure for this atom.
17. What is the electron arrangement for an atom of magnesium?
_____________________________________________________________________________
18. Draw the Bohr structure for this atom.
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JSSS
Student
19. Fill in the blank spaces in the table below.
Name
Symbol
Atomic
Number
Number Of
Electron
Number
Of
Electrons
Arrangement
Protons
Hydrogen
Helium
Lithium
Beryllium
Boron
Carbon
Nitrogen
Oxygen
Fluorine
Neon
Sodium
Magnesium
Aluminium
Silicon
Phosphorus
Sulfur
Chlorine
Argon
Potassium
Calcium
19. Using paper and modelling clay or plasticine, or pipe cleaners and plasticine, make
a model of (i) a lithium atom (ii) a potassium atom (iii) an aluminium atom.
Describe and draw your models.
Isotopes
The number of neutrons in an atom of a particular element is not always the same. For example,
some carbon atoms contain 6 neutrons each, others contain 7 neutrons each, and there are 8
neutrons each in other carbon atoms. Atoms of the same element that have a different number of
neutrons are called isotopes.
20. How many isotopes of carbon are there? ______________________________________
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