AS Chemistry Lesson 1 atomic structure

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AS ChemistryLesson 1 atomic structure

• Thursday, 09 March 2017

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Lesson objectives

• Atomic Structure
• (a) describe protons, neutrons and electrons in
  terms of relative charge and relative mass
• (b) describe the distribution of mass and charge
  within an atom
• (c) describe the contribution of protons and
  neutrons to the nucleus of an atom, in terms of
  atomic (proton) number and mass (nucleon) number
  
• (d) deduce the numbers of protons, neutrons and
  electrons in
• (i) an atom given its atomic and mass number,
• (ii) an ion given its atomic number, mass number
  and ionic charge
• (e) explain the term isotopes as atoms of an
  element with different numbers of neutrons and
  different masses

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Remember this is a model. It is the nuclear
model of an atom.
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Draw a labelled diagram for the structure of the
atom. This can be any atom or just a generic
diagram.
Structure of the atom
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Essential information
Sub-atomic particle Mass Charge Location



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Subatomic particle Relative mass Relative charge
Proton 1 1
Neutron 1 0
electron, e- 1/2000 -1
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• Some GCSE revision questions
• The number of protons that an element has
  determines what atoms it contains. For example,
  all carbon atoms have six protons. In any atom,
  which particle is present in the same number as
  the number of protons?  
• Using the properties of the subatomic particles
  explain why is there no overall charge on an
  atom? 
• Using the properties of the subatomic particles
  justify where most of the mass of an atom is
  found. 
• Using the structure of an atom determine where
  most of the matter (material) in an atom is
  distributed. 
• Why is the overall charge of the nucleus
  positive?

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Most of the atom is empty space!
If you imagine an atom being the size of Wembley
stadium, the nucleus would be about the size of a
football on the centre spot. The electrons would
be two peas flying around the whole stadium. The
rest of it emptiness.
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What is the structure of an atom?
Protons, neutrons and electrons are not evenly
distributed in an atom.
The protons and neutrons exist in a dense core at
the centre of the atom. This is called the
nucleus.
The electrons are spread out around the edge of
the atom. They orbit the nucleus in layers called
shells.
In an atom the number of positive protons is the
same as the number of negative electrons.
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Nucleus contains protons and neutrons, overall
charge is positive. Most of an atoms mass is
found here. Most of the atom is empty
space. Electrons give the atom its overall size
and shape.
An atom has no overall charge because the number
of positive protons is the same as the number of
negative electrons.
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Distribution of mass in an atom

• The nucleus of an atom takes up almost no space
• It is tiny but it makes up most of the mass of
  the atom
• This is because it contains protons and neutrons
  which both have a mass of 1, the electrons orbit
  the nucleus and have negligible mass
• It contains positive protons and neutral neutrons
  so it overall it is positive

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Distribution of matter in atoms

• The rest of the atom is mostly empty space
• There are negative electrons going around the
  nucleus really fast. They give the atom its
  overall size

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• The mass of an electron is negligible compared to
  a proton or neutron, this means you can usually
  ignore it.

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Isotopes

• The number of protons is what determines which
  element it is.
• 8 protons oxygen
• 2 protons helium
• But the number of neutrons can vary.
• If the neutrons vary then what else will vary?
• If neutrons vary then so does the atoms.
• .mass!

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Isotopes

• Definition
• Isotopes are atoms of the same element with
  different numbers of neutrons.
• Isotopes of an element will have
• different masses
• the same number of protons and electrons
• different numbers of neutrons
• Isotopes of an element react in exactly the same
  way because reactions involve electrons, neutrons
  have no effect on chemical reactions.

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Mass number (nucleon number) total number of
protons and neutrons in the nucleus
Element symbol
X
A
Z
Symbol for an isotope

• Atomic (proton) number
• Number of protons in the nucleus defines the
  element
• All atoms of the same element have the same
  number of protons

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Chlorine -35 and -37 are examples of isotopes
Different mass numbers mean different numbers of
neutrons
Cl
Cl
37
35
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18 neutrons 20 neutrons (35 17) (37
17)
The atomic numbers are the same. Both isotopes
have 17 electrons and 17 protons Remember Number
of neutrons mass number atomic number
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• It is the number and arrangement of electrons
  that decides the chemical properties of an
  element. Isotopes have the same configuration of
  electrons, so they have the same chemical
  properties.
• Isotopes of an element do have slightly different
  physical properties such as density and rates of
  diffusion, which is dependant on the mass of
  particles.

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Isotopes of Carbon

• Carbon is a mixture of three isotopes, for each
  of them complete the table

Isotope 12 6 13 6 14 6
Mass number
Atomic Number
No. of neutrons
C
C
C
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Isotope questions (actual exam ones)

• Hydrogen, deuterium and tritium are all isotopes
  of each other.
• Identify one similarity and one difference
  between these isotopes.
• Deuterium can be written as 2H. Determine the
  number of protons, neutrons and electrons in a
  neutral deuterium atom.
• Write a nuclear symbol for tritium, given that it
  has 2 neutrons.
• 2. A certain atom X has one less proton and two
  more neutrons than K. What are its atomic number
  and mass number?
• Explain in terms of sub atom particles, why C-12
  and C-14 are isotopes

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Ions

• What is an ion?
• It is an atom that is charged.
• How does this happen?
• Either by gaining or losing one or more
  electrons.
• DefinitionAn ion is a positively or negatively
  charged atom or (covalently bonded) group of
  atoms (a molecular ion)

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Ions

• Ions have different numbers of protons and
  electrons
• Negative ions have more electrons than protons
• e.g. Br- the negative charge means that theres
  one more electron than there are protons. Br has
  35 protons, so it must have 36 electrons. The
  overall charge is 35 36 -1

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• Positive ions have fewer electrons than protons
• e.g. Mg 2 charge means that theres 2 fewer
  electrons than there are protons. Mg has 12
  protons, so Mg 2 must have 10 electrons. The
  overall charge
• 12 10 2

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Ions

• Complete the table

Ion 23 11 35 17
Mass number, A
Atomic Number, Z
No. of protons
No. of neutrons
No. of electrons
Overall charge
Cl-
Na
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Ions questions

• a) How many protons, neutrons and electrons are
  in the following atoms and ions?
• b) Which are atoms and ions? How do you know?
• 173Li 2) 2411Na 3) 199F 4) 5526Fe
• 5) 3919 K 6) 199 F- 7) 3920 Ca 2 8) 178 O 2-