Exam Science

Question 1

Q1: What’s the difference between a pure substance and a mixture?

Answer 1

A: A pure substance has only one type of particle (e.g., water, gold); a mixture contains two or more substances (e.g., saltwater).

Question 2

Q2: What’s the difference between an atom and a molecule?

Answer 2

A: An atom is a single particle of an element; a molecule is two or more atoms bonded together.

Question 3

Q3: Define physical and chemical properties with examples.

Answer 3

A: Physical: observed without changing the substance (e.g., melting point); Chemical: how a substance reacts

Question 4

Q4: What is the formula for density and how do you calculate it?

Answer 4

A: Density = mass ÷ volume (D = m/V).

Question 5

Q5: Give examples of physical and chemical changes.

Answer 5

A: Physical: melting ice, cutting paper; Chemical: rusting, burning wood.

Question 6

A: Physical: melting ice, cutting paper; Chemical: rusting, burning wood.

Answer 6

A: Hydrogen = “pop” sound, Oxygen = relights splint, CO₂ = turns limewater cloudy.

Question 7

Q7: How is the periodic table organized?

Answer 7

A: By increasing atomic number; columns = groups, rows = periods.

Question 8

Q8: Name four chemical families and a property of each.

Answer 8

A: Alkali metals (very reactive), Alkaline earth (less reactive), Halogens (form salts), Noble gases (non-reactive).

Question 9

Q9: What’s the difference between a metal, nonmetal, and metalloid?

Answer 9

A: Metals conduct electricity and are shiny; nonmetals are dull and insulators; metalloids have properties of both.

Question 10

Q10: What particles make up an atom and where are they found?

Answer 10

A: Protons (+) and neutrons (0) in the nucleus; electrons (–) orbit around.

Question 11

Q11: How do you draw a Bohr-Rutherford diagram?

Answer 11

A: Show protons and neutrons in the nucleus; electrons in energy levels around the nucleus (up to 20 elements).

Question 12

Q12: What is the octet rule?

Answer 12

A: Atoms want 8 electrons in their outer shell to be stable.

Question 13

Q13: What’s the difference between ionic and covalent compounds?

Answer 13

A: Ionic = transfer of electrons (metal + nonmetal); Covalent = sharing electrons (nonmetal + nonmetal).

Question 14

Q14: What is an ion?

Answer 14

A: An atom that has gained or lost electrons to become charged.

Question 15

Q15: How do you count atoms in a compound like Ca(OH)₂?

Answer 15

A: 1 calcium, 2 oxygen, 2 hydrogen (5 total atoms).