Atoms & Sub‑atomic Particles
What is the name for the smallest particle that still retains the properties of an element?
Atom
What do we call a substance made of only one kind of atom?
Element
In which state of matter are particles most closely packed and only vibrating in place?
Solid
Define density in one sentence
Density = mass per unit volume
In a chemical reaction, the starting substances are called
Reactants
Which sub‑atomic particle has a positive charge and is found in the nucleus?
Proton
Give one example of a diatomic element found naturally as molecules of two atoms
H₂ or O₂ or N₂
Which state of matter has particles far apart, moving very fast, and with almost no forces between them?
Gas
Which will generally float on the other: oil or water? Explain using density.
Oil floats on water because oil has lower density
What are the new substances produced in a chemical reaction called?
Products
Explain why a neutral atom has no overall charge.
Because the number of protons equals the number of electrons
What is the difference between an element and a compound?
Element = one kind of atom (e.g., O₂ is oxygen element), Compound = two or more elements chemically bonded (e.g., H₂O)
Describe, in particle model terms, what happens to particles when a solid melts.
Particles gain energy, vibrate more, move apart into liquid arrangement
A metal rod is heated and its length increases. What is this process called and why does it happen at the particle level?
Expansion; particles move further apart due to increased kinetic energy
State what happens to atoms during a chemical reaction
Atoms rearrange / bonds break and form
State two differences between protons and electrons
Proton: positive, in nucleus; Electron: negative, orbitals
A compound always has its elements in a fixed ratio. Explain using water as your example.
Water = H₂O always two H atoms per one O atom
Explain why diffusion is faster in gases than in liquids using particle motion and spacing.
Because gas particles move faster and are farther apart so spread quicker
Two materials have the same mass but different volumes. Which has lower density?
Lower density if larger volume for same mass
When methane burns in oxygen to form carbon dioxide and water, mass appears conserved. Explain why the total number of atoms is the same before and after the reaction
Atoms are rearranged but not created or destroyed; total atom count unchanged (conservation of mass)
A certain neutral atom has 17 protons and 18 neutrons. What is its atomic number and why?
Atomic number = 17 because atomic number = number of protons
Describe one chemical method and one physical method that could separate a compound or mixture. State which applies to compounds and which to mixtures.
Chemical method for compounds: electrolysis or chemical decomposition
physical for mixtures: filtration, evaporation, distillation
A sealed container is heated, like in a microwave. Describe how particle speed, spacing, and pressure change.
Heating increases particle speed and spacing;
collisions with container walls increase, so pressure rises (unless container expands) and the lid pops off
Explain how gas pressure in a container changes when (a) you add more gas particles, and (b) you reduce the container volume. Use particle collisions in your answer.
(a) More particles → more collisions → pressure increases. (b) Smaller volume → more frequent collisions → pressure increases.
Describe an example from indigenous knowledge (given in the notes) that involves a chemical reaction, and name the reactants and one product.
Fermentation in brewing:
reactants (sugars) → products (alcohol and carbon dioxide)