Question

snc2p chemistry
name: ephi
topic 5: counting atoms

1. the ____ of an element represents one atom of that element.

• zn = ____ atom of zinc

1. a ____ is a number written at the lower right corner behind the symbol of an element.

• it shows how many ____ of an element exist in a molecule.
• f₂ = ____ atoms of fluorine in a molecule

1. a subscript outside a ____ multiplies all the elements inside the brackets.

ca(oh)₂ = __ calcium atom, oxygen atoms, __ hydrogen atoms
ba(po₄)₂ = __ barium atoms, phosphorus atoms, __ oxygen atoms

1. a __ is a number written in front of a chemical symbol. it indicates the number of __ of that element (used for balancing chemical equations).

• 3 co = ____ cobalt atoms

1. __ can also be written in front of a to indicate the number of __ of a compound.

3 h₂o =
____ water molecules
atom count: ____
2 caso₄=
____ molecules of calcium sulphate
atom count: ____
4 cu(no₃)₂ =
4 molecules of copper (ii) nitrate
atom count: 4 copper, 8 nitrogen, 24 oxygen

Explanation:

Step1: Recall chemical symbol concept

The chemical symbol of an element represents one atom of that element. So for "Zn", it represents 1 atom of zinc.

Step2: Recall sub - script concept

A subscript is a number written at the lower right corner behind the symbol of an element. It shows how many atoms of an element exist in a molecule. For "F₂", there are 2 atoms of fluorine in a molecule.

Step3: Analyze sub - script outside brackets

A subscript outside a bracket multiplies all the elements inside the brackets. For Ca(OH)₂, there is 1 calcium atom, 2 oxygen atoms (1×2 from OH₂), and 2 hydrogen atoms (1×2 from OH₂). For Ba(PO₄)₂, there is 1 barium atom, 2 phosphorus atoms (1×2 from PO₄₂), and 8 oxygen atoms (4×2 from PO₄₂).

Step4: Recall coefficient concept

A coefficient is a number written in front of a chemical symbol. It indicates the number of atoms of that element. For "3 Co", there are 3 cobalt atoms.

Step5: Apply coefficient to compounds

Coefficients can also be written in front of a chemical formula to indicate the number of molecules of a compound. For "3 H₂O", there are 3 water molecules, with a total of 6 hydrogen atoms (3×2) and 3 oxygen atoms (3×1), so the atom - count is 9. For "2 CaSO₄", there are 2 molecules of calcium sulphate, with 2 calcium atoms (2×1), 2 sulfur atoms (2×1) and 8 oxygen atoms (4×2), so the atom - count is 12.

Answer:

1. chemical symbol; 1
2. subscript; atoms; 2
3. bracket; 1; 2; 2; 1; 2; 8
4. coefficient; atoms; 3
5. Coefficient; chemical formula; molecules; 3; 9; 2; 12