Grade 8 Science Practice Test: The Periodic Table and Chemical Formulas
- The Periodic Table and Chemical Formulas
- 10 questions
- 13 minutes
Ten questions on how the periodic table is organized and how to read a chemical formula. Tip: a subscript counts atoms of the element right before it; a big number in front multiplies the whole formula.
Tap an option to mark your answer. You can change your mind, or tap the same option again to leave the question blank. The correct answers and explanations appear when you finish the test.Tap an option to answer; tap it again to leave the question blank.
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Question 1
Why do elements in the same column of the periodic table have similar properties?
Correct answer: D
Elements in a column, called a group, have the same number of electrons in their outer shell, which controls how they react. Their masses are different.
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Question 2
What are the horizontal rows of the periodic table called?
Correct answer: C
Rows are periods and columns are groups, also called families. Compounds are substances made of two or more elements, not parts of the table.
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Question 3
Carbon has an atomic number of 6. What does this tell you about every carbon atom?
Correct answer: A
The atomic number is the number of protons, and it is what makes an atom carbon. The number of neutrons can vary between carbon atoms.
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Question 4
Baking soda has the formula NaHCO3. How many atoms are in one formula unit?
Correct answer: B
Count each element: Na 1 + H 1 + C 1 + O 3 = 6 atoms. Answering 4 counts each element only once and ignores the subscript 3.
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Question 5
An element is dull, breaks easily when hammered and does not conduct electricity.
Where is it most likely found on the periodic table?
Correct answer: D
Dull, brittle, non-conducting solids are typical nonmetals, which are on the right side of the table. Metals are shiny and conduct electricity.
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Question 6
Neon, argon and helium are in group 18, the noble gases. What property do they share?
Correct answer: C
Noble gases have full outer electron shells, so they very rarely form compounds. That is why helium is safe to use in party balloons.
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Question 7
Sodium reacts strongly with water. Which element would most likely react with water in a similar way?
Correct answer: B
Potassium is in the same group as sodium (group 1, the alkali metals), so it reacts in a similar way. Chlorine and neon are in other groups.
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Question 8
How many hydrogen atoms are shown in 2H2O?
Correct answer: A
The coefficient 2 means two water molecules, and each has 2 hydrogen atoms: 2 × 2 = 4. Answering 2 forgets the coefficient.
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Question 9
Which of these substances is an element, not a compound?
Correct answer: D
O2 contains only oxygen atoms, so it is an element even though two atoms are joined. The others each contain two different elements.
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Question 10
In the equation 2H2 + O2 → 2H2O, how many oxygen atoms are on each side?
Correct answer: A
Left side: O2 has 2 oxygen atoms. Right side: 2H2O has 2 × 1 = 2. The equation is balanced, so atoms are conserved.
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