Elements & Compounds
What is the smallest unit of an element?
Atom
Name one physical property of matter.
Examples – color, shape, mass, volume, density, texture, boiling point.
Is ice melting a physical or chemical change?
(Answer: Physical change)
What does “dissolve” mean?
(Answer: When a substance breaks into small particles and spreads evenly in a liquid.)
Is tearing paper a physical or chemical change?
(Answer: Physical change)
Is water (H₂O) an element or a compound? Explain why
A compound, because it has hydrogen and oxygen chemically combined.
Why is weight considered a physical property?
(Answer: Because it can be measured without changing the substance.)
Burning wood is what type of change? Why?
(Answer: Chemical change – a new substance forms, like ash and smoke.)
What is a “precipitate”?
(Answer: A solid that forms when two liquids are mixed and a chemical reaction occurs.)
Is baking a cake a physical or chemical change?
(Answer: Chemical change – new substances are formed.
Which is a compound?
a) O₂
b) NaCl
c) Fe
NaCl – made of sodium and chlorine combined
Which of these is a physical property?
a) Ability to rust
b) Color
c) Flammability
Color
Which of the following is a chemical change?
a) Breaking glass
b) Salt dissolving in water
c) Rust forming on iron
(Answer: Rust forming on iron)
What is the difference between an element and a compound?
(Answer: An element is made of one kind of atom; a compound is made of two or more different atoms chemically combined.)
You mix vinegar and baking soda, and bubbles form. What kind of change is this, and what evidence supports it?
(Answer: Chemical change – evidence is gas production/bubbles.)
Question: Explain why hydrogen and oxygen are considered elements, but water is considered a compound. Then, describe whether forming water from hydrogen and oxygen is a physical change or a chemical change, and justify your answer.
Hydrogen and oxygen are elements because each is made of only one type of atom.
Water (H₂O) is a compound because it contains two different elements chemically bonded together.
Forming water is a chemical change because the reaction produces a new substance with properties different from hydrogen and oxygen.
Whats the definition of a physical property?
A physical property is something you can observe or measure about a substance without changing what it is.
Is Gas release considered a physical change?
No. Its a Chemical change
What is a atomic number?
What does the atomic number of an element tell us?
The atomic number of oxygen is 8. How many protons does oxygen have?
Answer: 8 protons