Atoms, Elements, Compounds
What is everything around us made of?
Atoms
What chemical symbol represents oxygen?
O
What is a mixture?
Two or more substances physically combined, not chemically bonded.
What are reactants?
The substances that take part in a chemical reaction.
Does a physical change form a new substance?
No
What is an element?
A pure substance made from one type of atom
In the formula CO₂, which elements are present?
Carbon and Oxygen
Is fruit salad homogeneous or heterogeneous?
Heterogenous
What are products?
The new substances formed in a chemical reaction.
Is melting chocolate a physical or chemical change?
Physical
What is a compound?
A substance made from two or more different elements
In H₂O, how many hydrogen atoms are shown?
2 Hydrogen atoms
Why is cordial mixed completely with water a homogeneous mixture?
Because the particles are evenly spread and the mixture has one appearance.
In the reaction carbon + oxygen → carbon dioxide, what is the product?
Carbon dioxide.
Name two signs that a chemical reaction may have occurred.
Examples: gas produced, colour change, temperature change, light produced, sound produced, new solid formed.
Why is Oxygen gas, ( O₂ ) still considered an element even though it is two atoms joined together?
Both atoms are the same type, meaning it is still a pure substance
What does the small number 3 mean in the formula NH₃?
There are three hydrogen atoms.
What is the difference between a solution and a suspension?
In a solution, the solute dissolves evenly and does not settle. In a suspension, particles do not dissolve and may settle over time.
In the reaction magnesium + acid → salt + hydrogen, name one reactant and one product.
Reactant: magnesium or acid. Product: salt or hydrogen.
Why is rusting iron a chemical change?
Iron reacts with oxygen to form a new substance: rust, or iron oxide.
Explain one key difference between a compound and an element referring to their particles
An element contains only one type of atom, while a compound contains two or more different types of atoms chemically bonded together.
A molecule contains 1 carbon atom and 4 hydrogen atoms. What is its chemical formula?
CH₄
Why can mixtures usually be separated using physical methods?
Because the substances are not chemically bonded together.
Explain why products in a chemical reaction are different from the reactants.
Bonds between atoms break and new bonds form, creating new substances with different properties.
Give three examples of physical changes.
Examples: melting, freezing, dissolving, cutting, crushing, boiling, evaporating.