Question

1. copy the table below in your exercise book. use the table to classify the following as atom, element, molecule and compound. one has been done for you.

a) oxygen
b) water
c) carbon (iv) oxide
d) table salt (sodium chloride)
e) argon
f) carbon
g) copper (ii) oxide
h) aluminium

atom element compound molecule
carbon carbon

1. a) write the symbols of the following elements.

i) calcium iii) carbon
ii) copper

Explanation:

1. Atom/Element/Molecule/Compound Classification:

• An atom is the smallest unit of an element. An element is a pure substance made of only one type of atom. A molecule is a group of two or more atoms held together by chemical bonds. A compound is a substance made up of two or more different - types of elements chemically combined.
• Oxygen ($O$) can exist as an atom. As an element, it is oxygen. Oxygen gas is a molecule ($O_2$) and not a compound as it is made of only one type of element.
• Water ($H_2O$) is a compound and a molecule as it is made of hydrogen and oxygen atoms chemically bonded.
• Carbon(IV) oxide ($CO_2$) is a compound and a molecule.
• Table - salt (sodium chloride, $NaCl$) is a compound.
• Argon ($Ar$) is an element and exists as single - atoms (a noble gas), so it is also an atom.
• Carbon ($C$) is an element and can be considered an atom in some contexts.
• Copper(II) oxide ($CuO$) is a compound.
• Aluminium ($Al$) is an element and can be considered an atom in some contexts.

1. Element Symbols:

• The symbol for calcium is $Ca$.
• The symbol for copper is $Cu$.
• The symbol for carbon is $C$.

Answer:

1.

Atom	Element	Compound	Molecule
		Water ($H_2O$)	Water ($H_2O$)
		Carbon(IV) oxide ($CO_2$)	Carbon(IV) oxide ($CO_2$)
		Table salt ($NaCl$)
Argon (Ar)	Argon
Carbon (C)	Carbon
		Copper(II) oxide ($CuO$)
Aluminium (Al)	Aluminium

2.

• i) $Ca$
• ii) $Cu$
• iii) $C$