Distinguish between mass number and relative atomic mass of an element - Leaving Cert Chemistry - Question 5 - 2013
Question 5
Distinguish between mass number and relative atomic mass of an element.
You will notice, from the values given on page 79 of the formulae and tables booklet, that t... show full transcript
Worked Solution & Example Answer:Distinguish between mass number and relative atomic mass of an element - Leaving Cert Chemistry - Question 5 - 2013
Step 1
Distinguish between mass number and relative atomic mass of an element.
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Answer
Mass number is defined as the total number of protons and neutrons in an atom's nucleus. It represents the sum of the nucleons.
Relative atomic mass, on the other hand, is the weighted average mass of the atoms of an element, based on the abundance of its isotopes. It is commonly not a whole number because it reflects a mixture of isotopes, averaged according to their natural occurrence.
Step 2
Give the reason for this:
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Answer
The relative atomic mass is rarely a whole number because elements exist as mixtures of isotopes, each with a different mass. The average reflects the proportions of these isotopes.
Step 3
Who was the Russian scientist?
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The Russian scientist was Dmitri Mendeleev.
Step 4
What is the order used in arranging the elements in the modern periodic table?
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The elements in the modern periodic table are arranged in order of increasing atomic number (Z), which corresponds to the number of protons in the nucleus.
Step 5
Explain the underlined term.
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A beta-particle is a high-speed electron (e⁻) emitted during radioactive decay, specifically in the process of beta decay. It represents the decay of a neutron into a proton, emitting an electron and an antineutrino.
Step 6
What is a beta-particle?
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A beta-particle is a type of radiation that consists of high-speed electrons or positrons, and is emitted during the beta decay of certain radioisotopes.
Step 7
Explain what is meant by the half-life of a radioactive isotope.
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The half-life of a radioactive isotope is the time required for half of the radioactive nuclei in a sample to decay. It indicates the stability of the isotope and the rate of decay.
Step 8
Give one use of carbon-14.
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Carbon-14 is commonly used in radiocarbon dating, which is a method for determining the age of ancient organic materials by measuring their carbon-14 content.
Step 9
Draw a diagram showing the arrangement of electrons in an atom of carbon-14.
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A diagram of the arrangement of electrons in a carbon-14 atom would show a nucleus with 6 protons and 8 neutrons, surrounded by 6 electrons arranged in two energy levels: 2 in the first shell and 4 in the second shell. The first shell can be filled with 2 electrons (•), and the second with 4 electrons (• • • •).
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