Download I. Atoms II. Chemical Symbols III. Structure

Atoms
I.
Atoms
Atoms are the basic building blocks that make up you and I as well as everything around us, both
living and non-living. A substance made up of one type of atom only is called an element. There
are currently 118 different elements of which 98 occur naturally, the others have been created
by humans.
The periodic table lists all the elements, with groups containing elements with similar
properties. For example the periodic table can be split with an invisible line with those to the
left of the being metals and those to the right non-metals.
II.
Chemical Symbols
Each element is represented by a chemical symbol. These chemical symbols are simply a letter
or two - the first letter always is a capital and the second letter, if there is one, always lower
case. These symbols can be found in the periodic table. The only two examples you need to learn
are O for oxygen and Na for sodium.
III.
Structure
Each atom consists of a small central nucleus made of protons and neutrons. Around this
nucleus are electrons.
Neutrons have no electrical charge.
Protons have a positive charge. Electrons have a negative charge. The atom has no overall
electrical charge - the number of protons is equal to the number of electrons so the positive and
negative charges balance out.
IV.
Atomic Number
You will see in the periodic table that elements are shown as their chemical symbol with two
numbers usually above and below, for example oxygen -
16
O8 .
The top number here (for oxygen 8) is the element’s atomic number. This is the number of
protons in the element; therefore every atom of oxygen has 8 protons in its nucleus. Each
specific element has a specific number of protons. If an atom has the same number of protons as
another, the two are the same element. If an atom has a different number of protons to the
other atom then they are different elements.
Note the number of protons is equal to the number of electrons.
In the periodic table the elements are arranged in order of their atomic number.
V.
Mass Number
Going back to our example oxygen -
16
O8
The bottom number here (for oxygen 16) is the element’s mass number. This is the total of
protons and neutrons in the atom; therefore each atom of oxygen has 16 protons and neutrons
in total. Given that there are 8 protons (atomic number 8) there are therefore 8 neutrons.
Oxygen therefore has 8 neutrons, 8 protons and 8 electrons.
VI.
Electrons
The electrons around the nucleus are organised into different energy levels/shells. The inner
energy levels/shells are occupied first, the filling up outwards. Each energy level/shell can only
hold a certain number of electrons as detailed in the table below for the first 3 level/shells.
Energy level/shell
Maximum Number of
Electrons
1st
2
2nd
8
3rd
8
The electronic structure of any atom can be represented in a diagram as follows:
Li 2,1
Na 2,8,1
Mg 2,8,2
MCQ
1. Approximately how many elements are there in the periodic table?
a) 10
b) 28
c) 365
d) 100
2. Which element is represented by the symbol Na?
a) Oxygen
b) Sodium
c) Nitrogen
d) Carbon
3. What is the relative electrical charge of a proton?
a) 0
b) -1
c) +1
d) +2
4. What does the mass number of an element tell us?
a) the number of protons plus neutrons
b) the number of electrons plus protons
c) the number of electrons plus neutrons
d) the number of neutrons in the nucleus
5. Lithium has an atomic number of 3 and a mass number of 7, how many neutrons does Lithium
have in each atom?
a) 4
b) 3
c) 7
d) 2
6. Where in the atom are electrons found?
a) in the nucleus
b) throughout the atom
c) in energy levels/shells around the nucleus
d) in lines radiating out from the nucleus
7. If an element has 45 protons, 45 electrons and 58 neutrons, what is its mass number?
a) 45
b) 103
c) 90
d) 116
8. Sodium has 11 electrons, how are these arranged?
a) 8,3
b) 2,4,7
c) 2,8,1
d) 2,9
9. An element has 2 electron shells/levels with 6 in the outer shell, which element is it?
a) Sodium
b) Carbon
c) Nitrogen
d) Oxygen
10. All atoms of a particular element have the same number of ____________?
a) protons
b) electrons
c) neutrons
d) none of the above
ANSWER
1d 2b 3c 4a 5a 6c 7b 8c 9d 10a