Principles of Chemistry
7 marks · EasyThis question is about atoms, molecules and the Periodic Table.
Define the term atom.
Define the term molecule.
Hydrogen and oxygen are both elements. Using their positions in the Periodic Table, state which has a higher atomic number.
Two atoms of hydrogen bond with one atom of oxygen to form water. What is the chemical formula of a water molecule?
State one way in which the arrangement of elements in the Periodic Table is related to atomic number.
Give a reason why all atoms of a particular element (for example, carbon) have the same chemical properties.
Explain why the noble gases are found in Group 0 of the Periodic Table.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) An atom is the smallest part of an element that can still be recognised as that element. · must show smallest piece of element, retains properties
(b) A molecule is two or more atoms chemically bonded together. · must show two or more atoms, chemically bonded
(c) Oxygen · must show oxygen
(d) H2O · must show H2O
(e) The elements are arranged in order of increasing atomic number. · must show atomic number increases
(f) Because they have the same number and arrangement of electrons. · must show same number of electrons
(g) Because they have full outer shells of electrons and are very unreactive. · must show full outer shell, unreactive
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correctly defines atom as smallest part of an element retaining its properties.
B1 (b) · 1 mark · Correctly defines molecule as two or more atoms chemically bonded.
B1 (c) · 1 mark · States correctly that oxygen has the higher atomic number.
B1 (d) · 1 mark · Gives H2O as the correct chemical formula for water.
B1 (e) · 1 mark · States that periodic table is arranged by increasing atomic number.
B1 (f) · 1 mark · Gives reason for chemical similarity as same (number/arrangement of) electrons.
B1 (g) · 1 mark · Explains noble gases are in Group 0 due to full outer electron shells and unreactive nature.
Worked solution
a) An atom is the smallest particle of an element that can still be identified as that element.
b) A molecule is made when two or more atoms are chemically bonded together.
c) Oxygen is to the right of hydrogen in the Periodic Table and has a higher atomic number.
d) Water is formed from two hydrogen atoms and one oxygen atom: formula is H2O.
e) Elements are arranged in the Periodic Table in increasing order of atomic number.
f) All atoms of a particular element have the same number and arrangement of electrons, giving them the same chemical properties.
g) Noble gases have full outer electron shells, making them very unreactive; this is why they are in Group 0.