Download Atomic Structure * Learning Outcomes

1
Atomic Structure – Learning Outcomes
 Describe the structure of the atom.
 State the location, relative charge, and atomic mass of
the sub-atomic particles.
 HL: Define atomic number.
 HL: Draw the Bohr structure of the first 20 elements.
 HL: Define isotope.
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Describe the Structure of the Atom
 An atom is the smallest particle of an element which still
retains the properties of that element.
 Atoms have a solid core called the nucleus.
 The nucleus contains two types of sub-atomic particles –
protons and neutrons.
 The nucleus is surrounded by mostly empty space.
 The empty space contains shells where another subatomic particle, electrons are found.
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State Facts About Sub-Atomic Particles
 The location, charge, and atomic mass of sub-atomic
particles are how they are distinguished.
 These masses and charges are so small (e.g. mass of
proton = 0.000 000 000 000 000 000 000 000 001 67 kg),
that we use new units more suitable.
 For mass, we use atomic mass units (u) and for charge,
we use elementary charge.
Particle
Proton
Neutron
Electron
Location
Nucleus
Nucleus
Outside the
nucleus
Charge
+1
0
-1
Atomic Mass
1
1
1
1850
by 2012rc – CC-BY-SA-3.0
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Define Atomic Number
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Define Atomic Number
 The atomic number of an atom is the
number of protons in its nucleus.
 Most of the time, this is also the
number of electrons the atom has
orbiting it.
 The mass number of an atom is the
sum of protons and neutrons in its
nucleus.
 i.e. #neutrons + #protons = mass
number
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Draw Bohr Structure
 Protons and neutrons always exist in the nucleus.
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Draw Bohr Structure
 Electrons are more complicated:
 They exist outside the nucleus.
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Draw Bohr Structure
 They exist in pairs where possible.
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Draw Bohr Structure
 Shells have a maximum amount of space. The first shell
takes two electrons. A new shell is needed to add more.
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Draw Bohr Structure
 Pairs on each shell spread away from each other.
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Draw Bohr Structure
 The second and third shells hold 8 electrons each.
 Remember the first shell can only hold 2.
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Draw Bohr Structure
 These rules combined give the Bohr structure of the
atom.
 On our course, we need to be able to draw the Bohr
structure of the first 20 elements.
 Draw the Bohr structure for:
 Hydrogen (𝐻11 )
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 Sodium 𝑁𝑎23
 Helium 𝐻𝑒42
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 Silicon 𝑆𝑖28
 Lithium (𝐿𝑖73 )
18
 Argon 𝐴𝑟40
8
 Oxygen 𝑂16
19
 Potassium 𝐾39
10
 Neon (𝑁𝑒20
)
20
 Calcium (𝐶𝑎40
)
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Define Isotope
 Each element is defined by its atomic number.
 Notice that the mass number on the periodic table
comes with decimals.
 e.g. the mass number of hydrogen is given as 1.00794.
 Every hydrogen has 1 proton (that’s what makes it
hydrogen), but some hydrogens have different numbers
of neutrons in their nucleus.
 Hydrogen-1 has 1 proton, 0 neutrons (total mass 1)
 Hydrogen-2 has 1 proton, 1 neutron (total mass 2)
 Hydrogen-3 has 1 proton, 2 neutrons (total mass 3)
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Define Isotope
 Isotopes are atoms with the same atomic number but
different mass numbers.
 The 1.00794 given as the mass of hydrogen on the
periodic table is an average value for the mass of
hydrogen.
 Since hydrogen-1 is much, much more common than
hydrogen-2 or hydrogen-3, the average mass (relative
atomic mass) is very close to 1.