5. (a) Define (i) atomic number, (ii) mass number - Leaving Cert Chemistry - Question 5 - 2011
Question 5
5. (a) Define (i) atomic number, (ii) mass number.
(b) Name the English scientist, pictured on the right, who identified electrons as negatively charged subatomic p... show full transcript
Worked Solution & Example Answer:5. (a) Define (i) atomic number, (ii) mass number - Leaving Cert Chemistry - Question 5 - 2011
Step 1
Define (i) atomic number
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Answer
The atomic number is defined as the number of protons in the nucleus of an atom of an element. It determines the identity of the element.
Step 2
Define (ii) mass number
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Answer
The mass number is defined as the total number of protons and neutrons in the nucleus of an atom. It represents the mass of the atom in atomic mass units (amu).
Step 3
Name the English scientist, pictured on the right, who identified electrons as negatively charged subatomic particles in the 1890s.
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Answer
The scientist is J.J. Thomson.
Step 4
What is the maximum number of electrons that can occupy the second shell (main energy level)?
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Answer
The maximum number of electrons that can occupy the second shell is 8. This follows the formula: 2n2, where n is the shell number.
Step 5
Draw a diagram showing the arrangement of electrons in an oxygen atom. Use dots (•) or crosses (x) to represent the electrons.
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Answer
The electron arrangement for an oxygen atom (8 electrons) can be represented as follows:
• •
• • • •
This shows 2 electrons in the first shell and 6 in the second.
Step 6
Define electronegativity
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Electronegativity is a measure of the relative attraction an atom has for a shared pair of electrons in a covalent bond.
Step 7
Use electronegativity values to predict the type of bonding that occurs in a water molecule.
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Answer
The water molecule (H2O) has polar covalent bonds due to the difference in electronegativity between hydrogen and oxygen.
Step 8
Draw a dot and cross diagram to show the bonding in a water molecule.
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Answer
The bonding in the water molecule can be illustrated as:
• •
H—O—H
x x
Here, '•' represents the electrons from the oxygen atom and 'x' represents the electrons from the hydrogen atoms.
Step 9
State the shape of a water molecule.
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Answer
The shape of a water molecule is angular or v-shaped due to the two lone pairs of electrons on the oxygen atom.
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