Elements & compounds worksheet - Free Printable
Educational worksheet: Elements & compounds worksheet. Download and print for classroom or home learning activities.
JPG:LARGE
1450×2014
194.8 KB
Free · Personal Use
Quality Assured by Worksheets Library Team
Reviewed for educational accuracy and age-appropriateness
ID: #1250120
⭐
Show Answer Key & Explanations
Step-by-step solution for: Elements & compounds worksheet
▼
Show Answer Key & Explanations
Step-by-step solution for: Elements & compounds worksheet
Let’s go through each part of the worksheet step by step.
---
1a. Approximately how many elements have been discovered?
We know from science that there are 118 confirmed elements on the periodic table (as of now). So, “approximately 100” is the closest correct answer.
✔ Circle: 100
---
1b. Which of the following is true about the atoms in an element?
An element is made up of only one type of atom. That means all atoms in a pure element are the same — they have the same number of protons.
So the correct choice is:
✔ All of the atoms in an element are the same
---
1c. The diagrams below show the atoms in three different substances. Which could show an element and which could not?
Remember: An element has only one kind of atom. A compound has two or more kinds of atoms bonded together. A mixture has different substances mixed but not chemically bonded.
Let’s look at each diagram:
🔹 Top diagram: All circles are identical and packed together.
→ This shows only one type of atom → ✔ Could be an element
Explanation: All atoms are the same, so it fits the definition of an element.
🔹 Middle diagram: Each group has one big circle and two small circles attached.
→ These are molecules made of different atoms → ✘ Could NOT be an element
Explanation: Each unit has more than one type of atom, so it’s a compound, not an element.
🔹 Bottom diagram: All groups are pairs of identical small circles.
→ Each molecule has two of the same atom → ✔ Could be an element
Explanation: Even though they’re in pairs (like O₂ or H₂), they’re still only one type of atom — so it can be an element.
---
1d. Methane is a compound with the formula CH₄. Explain why we cannot find methane on the periodic table.
The periodic table lists elements, not compounds. Methane is made of carbon and hydrogen atoms bonded together — that makes it a compound. Compounds don’t appear on the periodic table; only individual elements do.
✔ Answer: Because methane is a compound made of two different elements (carbon and hydrogen), and the periodic table only shows elements, not compounds.
---
1e. A student wrote the symbol for cobalt as CO. Explain why this is incorrect and what this actually shows.
Cobalt’s correct symbol is Co (capital C, lowercase o). If you write “CO”, that means something else: Carbon (C) and Oxygen (O) — which is carbon monoxide, a compound.
✔ Answer: It’s incorrect because cobalt’s symbol is Co, not CO. CO stands for carbon monoxide, which is a compound made of carbon and oxygen.
---
Final Answer:
1a. 100
1b. All of the atoms in an element are the same
1c. Top: Could be an element — all atoms are the same. Middle: Could not be an element — atoms are different types bonded together. Bottom: Could be an element — all atoms are the same, even if paired.
1d. Methane is a compound, and the periodic table only lists elements.
1e. Cobalt’s symbol is Co, not CO. CO means carbon monoxide, a compound of carbon and oxygen.
---
1a. Approximately how many elements have been discovered?
We know from science that there are 118 confirmed elements on the periodic table (as of now). So, “approximately 100” is the closest correct answer.
✔ Circle: 100
---
1b. Which of the following is true about the atoms in an element?
An element is made up of only one type of atom. That means all atoms in a pure element are the same — they have the same number of protons.
So the correct choice is:
✔ All of the atoms in an element are the same
---
1c. The diagrams below show the atoms in three different substances. Which could show an element and which could not?
Remember: An element has only one kind of atom. A compound has two or more kinds of atoms bonded together. A mixture has different substances mixed but not chemically bonded.
Let’s look at each diagram:
🔹 Top diagram: All circles are identical and packed together.
→ This shows only one type of atom → ✔ Could be an element
Explanation: All atoms are the same, so it fits the definition of an element.
🔹 Middle diagram: Each group has one big circle and two small circles attached.
→ These are molecules made of different atoms → ✘ Could NOT be an element
Explanation: Each unit has more than one type of atom, so it’s a compound, not an element.
🔹 Bottom diagram: All groups are pairs of identical small circles.
→ Each molecule has two of the same atom → ✔ Could be an element
Explanation: Even though they’re in pairs (like O₂ or H₂), they’re still only one type of atom — so it can be an element.
---
1d. Methane is a compound with the formula CH₄. Explain why we cannot find methane on the periodic table.
The periodic table lists elements, not compounds. Methane is made of carbon and hydrogen atoms bonded together — that makes it a compound. Compounds don’t appear on the periodic table; only individual elements do.
✔ Answer: Because methane is a compound made of two different elements (carbon and hydrogen), and the periodic table only shows elements, not compounds.
---
1e. A student wrote the symbol for cobalt as CO. Explain why this is incorrect and what this actually shows.
Cobalt’s correct symbol is Co (capital C, lowercase o). If you write “CO”, that means something else: Carbon (C) and Oxygen (O) — which is carbon monoxide, a compound.
✔ Answer: It’s incorrect because cobalt’s symbol is Co, not CO. CO stands for carbon monoxide, which is a compound made of carbon and oxygen.
---
Final Answer:
1a. 100
1b. All of the atoms in an element are the same
1c. Top: Could be an element — all atoms are the same. Middle: Could not be an element — atoms are different types bonded together. Bottom: Could be an element — all atoms are the same, even if paired.
1d. Methane is a compound, and the periodic table only lists elements.
1e. Cobalt’s symbol is Co, not CO. CO means carbon monoxide, a compound of carbon and oxygen.
Parent Tip: Review the logic above to help your child master the concept of elements and compounds worksheet.
