Test: Making compounds - Year 7 MCQ

The easy way to do this is to count the capital letters in the formula. Each element has exactly ONE capital letter. In CaCO₃, the three elements are Ca, C and O

When iron reacts with sulfur, they form a binary compound called iron sulfide (FeS), indicated by the "-ide" suffix for compounds of two elements. Iron oxide (A) requires oxygen, not sulfur. "Sulfuric iron" (B) is not a valid compound name. Sulfuric acid (D) is a compound of hydrogen, sulfur, and oxygen, not formed by iron and sulfur alone.

Methane (CH4) contains one carbon atom and four hydrogen atoms, totaling five atoms, making option A correct. Option B is incorrect because methane has only two different elements (carbon and hydrogen), not five. Option C is incorrect because methane is a molecule, not an atom, and it contains two different elements. Option D is incorrect because CH4 represents one molecule, not five.

Chlorine (Cl₂) is an element, as it consists of only one type of atom and appears on the periodic table. Carbon monoxide (CO), hydrochloric acid (HCl), and propane (C₃H₈) are compounds, as they are made of two or more different elements chemically bonded.

In molecular compounds, the atoms bind to each other through covalent bonds.

Table salt (NaCl) is an ionic compound, commonly referred to as a salt, and is held together by ionic bonds. It is not a molecular compound (A), which involves covalent bonds, nor an organic compound (B), which contains carbon-hydrogen bonds, nor an acid (D), which releases H+ ions in solution.

When elements combine to form a compound, they lose their individual properties and the newly formed compound has new properties.

The equation "Hydrogen + chlorine → hydrogen chlorine" (B) is incorrect because the compound formed is hydrogen chloride (HCl), with "chloride" as the correct suffix for the compound. The other equations are correct: copper oxide (CuO), iron chloride (FeCl₂ or FeCl₃), and magnesium oxide (MgO) use proper naming conventions for binary compounds.

NaCl (table salt) is a salt, held together by ionic bonds. H₂O (A) is a molecular compound, CO₂ (B) is a molecular compound, and CH₄ (D) is a molecular compound, none of which are salts.

In NaCl, the sodium and chlorine atoms are held together by ionic bonds.