Atoms, Molecules, Compounds & Counting
What is the smallest unit of an element? and give an example!
(atom)
Which bond forms between a nonmetal and a nonmetal?
covalent bond
In a chemical equation, what are the starting substances called?
(reactants)
A beaker with no lid is what type of system?
open system
What type of reaction is A + B → AB ?
(synthesis)
How many total atoms are in H₂O?
(3 atoms)
Which bond forms between a metal and a nonmetal?
ionic bond
In a chemical equation, what are the substances made called?
(products)
A sealed container where gas cannot escape is what type of system?
closed system
What type of reaction is AB → A + B ?
(decomposition)
How many hydrogen atoms are in 2CH₄?
8 hydrogens
Describe what happens to electrons in a covalent bond.
Electrons are shared between atoms.
Why must chemical equations be balanced?
Because of the Law of Conservation of Mass — atoms are not created or destroyed.
A piece of steel wool is burned in an open container on a scale. The final mass is higher than the starting mass. Explain why and include the type of system.
Oxygen from the air combined with the iron during the reaction, so mass was added to the open system.
What type of reaction is A + BC → AC + B ?
(single replacement)
How many total atoms are in Ca(OH)₂?
5 atoms
Describe what happens to electrons in an ionic bond.
Electrons are transferred from one atom to another.
Is this equation balanced or unbalanced?
CH₄ + 2O₂ → CO₂ + 2H₂O
(Balanced)
Two students react vinegar and baking soda. Student 1 leaves the container open. Student 2 seals it with a balloon. Whose container will show a greater decrease in mass on the scale and why?
Student 1 — gas escapes in the open system, removing mass from the container.
What type of reaction is AB + CD → AD + CB ?
(double replacement)
What is the difference between a molecule and a compound?
A molecule is atoms bonded together; a compound is a molecule made of two or more different elements
Which is more likely to be ionic: NaCl or CO₂? Explain why.
NaCl — metal + nonmetal vs. two nonmetals in CO₂.
Is this equation balanced or unbalanced?
Al + O₂ → Al₂O₂
(Unbalanced)
Which system — open or closed — best shows the Law of Conservation of Mass, and explain how the other system can appear to gain or lose mass while the Law of Conservation of Mass is still true?
The closed system best shows the Law of Conservation of Mass because all matter (including any gases) is contained, so total mass stays the same.
In an open system, mass can appear to increase (if gas from the air enters/reacts) or decrease (if gas escapes), but the Law of Conservation of Mass is still true because matter is not destroyed — it just moves into or out of the system.
Name two things that could increase the rate of a chemical reaction.
(Higher temperature, higher concentration, more surface area, or a catalyst.)