S1.2 Nuclear Atom

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18 Terms

1
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What are subatomic particles?

  • The protons, neutrons and electrons that an atom is made up of are called subatomic particles

  • Protons have a relative mass of 1 and a relative charge of +1

  • Neutrons have a relative mass of 1 and a relative charge of 0

  • Electrons have a relative mass of weell and a relative charge of -1

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Why are they referred to as relative charge and relative mass?

Subatomic particles are so small that they cannot be measured through normal units and thus, their mass is comparative/in comparison to each other.

It is also referred to as relative charge, because it is in comparison to each other.

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Define Mass number

The mass number determines the mass of an atom and is the total number of nucleons in an atom.

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Define atomic number

the number of protons in the nucleus of an atom

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Why is a typical atom neutral?

In a typical atom, the number of protons, which are positively charged are equal to the number of electrons, which are negatively charged and so, they cancel each other out

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Define the Nuclear Notation

  • It is the way elements are presented

  • The upper number is the mass number known as A

  • The lower number is the atomic number known as Z

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What are the roles of protons, neutrons and electrons?

Protons :

  • The number of protons in an atom determines its atomic number, which in turn identifies the element.

  • Protons contribute to the overall positive charge of the nucleus.

  • In chemical reactions, the number of protons remains constant

Neutrons:

  • Neutrons are neutrally charged particles found in the nucleus of an atom.

  • Neutrons contribute to the mass of the atom without significantly affecting its chemical properties (except in nuclear reactions).

  • The number of neutrons can vary within atoms of the same element, giving rise to isotopes.

  • Neutrons help stabilize the nucleus by counteracting the repulsive forces between positively charged protons.

Electrons:

  • Electrons are negatively charged particles that orbit the nucleus of an atom in specific energy levels or shells.

  • Electrons determine the chemical behavior of an atom, as they participate in bonding with other atoms to form molecules and compounds.

  • The number and arrangement of electrons determine the atom's size, shape, and reactivity.

  • Electrons are involved in various chemical reactions

  • Electrons are also involved in phenomena such as electricity and magnetism due to their charge and motion.

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Describe the structure of an atom

  • Atoms have a a positively charged, dense nucleus

  • This is because the nucleus has protons and because most of the mass of an electron is concentrated there

  • Negative electrons occupy the space outside the nucleus, electron cloud

  • The electrostatic attraction between the positive nucleus and negatively charged electrons orbiting around it is what holds an atom together

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Define Ions

  • ions are atoms or molecules that have gained or lost one or more electrons, thus acquiring a net electrical charge.

  • When an atom gains electrons, it becomes negatively charged and is called an anion. When an atom loses electrons, it becomes positively charged and is called a cation.

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Define Isotopes

  • different atoms of the same element that contain the same number of protons and electrons but a different number of neutrons

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Define Relative Atomic Mass

  • the average mass of one atom of an element compared to one twelfth of the mass of an atom of carbon-12'

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How do you calculate relative atomic mass using abundance values?

total mass of 100 atoms = (% abundanceA x massA) + (% abundanceB x massB) 

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What is a mass spectrometer?

  • an instrument to accurately determine the relative atomic mass

  • separates atoms or molecules based on their charge

  • this can be used to identify substances

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Describe the layout of a mass spectrometer

  • There are four key stages

  • Ionisation where atoms are converted to ions

  • Acceleration where ions are accelerated

  • Deflection according to their mass and charge

  • Detection arrival at detector

→ this must happen in a vaccum so ions do not collide with air molecules which may stop them from reaching the detector

→ must be in gaseous state

<ul><li><p>There are four key stages </p></li><li><p>Ionisation where atoms are converted to ions</p></li><li><p>Acceleration where ions are accelerated</p></li><li><p>Deflection according to their mass and charge</p></li><li><p>Detection arrival at detector</p></li></ul><p>→ this must happen in a vaccum so ions do not collide with air molecules which may stop them from reaching the detector </p><p>→ must be in gaseous state </p>
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Describe Stage 1

Ionisation

  • A beam of electrons knock into electrons from atoms or molecules in the sample

  • Nearly all will lose at least one electron even the noble gasses and non-metals which typically gain electrons

  • In this case, all ions in a mass spectrometer are positive

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Describe Stage 2

Acceleration

  • The ions are accelerated so they have the same energy

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Describe Stage 3

Deflection

  • Ions deflected by a magnetic field according to the ratio of their mass to charge (m/z)

  • heavier ions are deflected less than lighter ones

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Describe Stage 4

Detection

  • Magnetic field is gradually increased which increases deflection

  • allows ions of increasing mass to enter the detector

  • when striking the detector they accept electrons, lose charge and create a current

  • current is proportional to abundance of each ions