Download Representing Elements and Atoms

Representing Elements
and Atoms
What’s in an atom?
 We now know the atom is made of 3
subatomic particles
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Protons (in the nucleus)
Neutrons (in the nucleus)
Electrons (orbits the nucleus)
 We also know electrons orbit the nucleus in
specific regions, at a fixed distance from the
centre
What’s in an atom?

Each subatomic particle has its own set of
properties
What’s in an atom?

Complete the properties chart:
Name
Relative Mass
Proton
1
Neutron
1
Electron
1/1840 (~ 0.0005)
Electric Charge
Location
In the Nucleus….
 Protons and neutrons contribute
nearly all the mass of the atom

The mass of an electron is so small it is
deemed “negligible”
• What does negligible mean?
Relative Size
Charge
 Every proton carries exactly the same
amount of positive charge (+1)
 Every electron carries exactly the same
amount of negative charge (-1)
 Every electron carries a negative charge
exactly opposite that of a proton.
Atomic Number
 The number of protons in an atom = atomic
number
 The atomic number identifies an atom as a
specific element


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Eg. Atomic number 6 means this atom has 6
protons in it
Only carbon has 6 protons
If a proton is somehow added to this atom, it is no
longer carbon - it becomes nitrogen (atomic
number 7), a completely different element
Mass Number
 Mass number = # protons + # neutrons
 If I know the mass number, how can I
determine the number of neutrons in an
atom?


# neutrons = mass number – atomic number
= total # P & N – # P
# neutrons in Na = 23 – 11
= 12
Number of Subatomic Particles
 How do you find the number of electrons?


In a neutral atom, positive charge = negative
charge
Therefore, # protons must = # electrons since
they have equal, but opposite charge
Number of Electrons
 Ex. In a neutral carbon atom, how many
electrons are there?


Carbon’s atomic number is 6. Therefore, there
are 6 protons.
Since there are 6 protons, there must also be 6
electrons to balance the charge
• (+6) + (-6) = 0
Gives you an
atom with no
overall charge
6 protons x (+1)
charge each
6 electrons x (-1)
charge each
Shorthand Notation for Elements
 The same way it is easier to write 5678 -
instead of five thousand six hundred seventyeight, we need a shortcut for atoms of
elements
 Each element has its own symbol.
This is a
universal ‘language’ for all scientists.



Na  sodium
K  potassium
C  carbon
Shorthand Notation for Elements
 The symbol is always a capital letter first




Ar
Ne
B
Remember:
 Atomic number = a whole number (no decimal)
 Atomic mass = usually a decimal (an average of
the # neutrons)
Isotopes

Isotopes: Atoms with the same number of protons
but a different number of neutrons.


Different varieties of the same element
2 common isotopes are Carbon-14 and Carbon-12.

Both isotopes are carbon because they each have 6
protons

They are different because C-14 has 8 neutrons and
C-12 only has 6

While C-12 is the most abundant (common) isotope
of carbon, both are called isotopes
Isotopes

Here is the isotopic notation for carbon 14.

How many protons, neutrons and electrons?

Protons- Carbon’s atomic number is 6,
 Therefore there are 6 protons

Electrons- If the atom is neutral, the number of protons =
the number of electrons
 Therefore there are also 6 electrons

Neutrons- The mass number equals the number of protons
+ neutrons,
 Therefore 14-6 leaves 8 neutrons
Standard Atomic Notation
 Homework:



Learn the first 20 symbols
Learn the first 20 element names in order
(Atomic numbers 1-20)
Spelling included!
Homework
Element symbol Element name
1
H
Hydrogen
2
He
Helium
3
Li
Lithium
4
…
…
5
…
…
…etc
…
…