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The English scientist, pictured on the right, introduced his atomic theory in the early 1800s - Leaving Cert Chemistry - Question 5 - 2010
Question 5
The English scientist, pictured on the right, introduced his atomic theory in the early 1800s. He stated that all matter is made up of tiny, indivisible particles ca... show full transcript
Worked Solution & Example Answer:The English scientist, pictured on the right, introduced his atomic theory in the early 1800s - Leaving Cert Chemistry - Question 5 - 2010
Step 2
Explain by reference to a named element why he was incorrect in stating that all the atoms of a particular element have the same mass.
Answer
Dalton stated that all atoms of a particular element are identical in mass. However, this is incorrect as demonstrated by isotopes. For example, carbon exists in forms such as carbon-12 and carbon-14, which have different masses because they contain different numbers of neutrons.
Step 3
Step 5
Explain how these valencies arise by reference to the noble gases.
Answer
Nitrogen requires 3 electrons to attain the electron configuration of neon, which is a noble gas. Similarly, hydrogen needs 1 electron to achieve the same electron configuration as helium, another noble gas. This is why nitrogen exhibits a valency of 3 and hydrogen a valency of 1 when forming ammonia.
Step 6
Use dot and cross diagrams to describe the bonding in the ammonia molecule.
Answer
The dot and cross diagram for ammonia (NH₃) would show nitrogen with 5 electrons in total: 3 shared with 3 hydrogen atoms and 2 remaining as non-bonding pairs. The diagram visually demonstrates the sharing of electrons between nitrogen and hydrogen, highlighting the covalent bonds formed.
Shape: The shape of the ammonia molecule is pyramidal, which arises from the arrangement of the bonding and lone pairs of electrons.
Step 7
Step 8
Use electronegativity values to predict the type of bond formed between nitrogen and hydrogen.
Answer
Nitrogen has a higher electronegativity than hydrogen, leading to a polar covalent bond between them. This occurs because the shared electrons are drawn closer to the nitrogen atom, giving it a partial negative charge while the hydrogen atom acquires a partial positive charge, indicating that the bond between them is polar.