Substances and Mixtures
A pure substance made of only one type of atom is called a _______.
Element
What state of matter has a definite shape and definite volume?
Solid
Who proposed the Law of Conservation of Mass?
Antoine Lavoisier
Who was the first to propose that matter is made of tiny indivisible particles called “atomos”?
Democritus
The number of protons in an atom is called the ________.
Atomic number
Salt water is an example of what type of mixture?
Homogeneous mixture / solution
Melting ice is what kind of change: physical or chemical?
Physical change
What does the Law of Conservation of Mass state?
Mass is neither created nor destroyed in a chemical reaction
Who discovered the electron, and with what experiment?
J.J. Thomson, cathode ray tube experiment
What is the mass number of an atom?
The total number of protons + neutrons
Sand and iron filings can be separated using which method?
Magnetism
When liquid water turns into gas, what is the process called?
Evaporation / Vaporization
The Law of Definite Proportions says what about compounds?
They always contain elements in the same fixed ratio by mass.
Rutherford’s gold foil experiment led to the discovery of what?
The nucleus / protons concentrated in a dense center
Atoms of the same element with different numbers of neutrons are called ________.
Isotopes
What’s the difference between a compound and a mixture?
A compound has atoms chemically bonded in fixed ratios, a mixture is physically combined and ratios vary
Explain why the particles in a liquid can flow past one another but those in a solid cannot.
Liquids have weaker intermolecular forces; solids have tightly packed, fixed particles
The Law of Multiple Proportions was proposed by which scientist?
John Dalton
Who discovered the neutron?
James Chadwick
Which scientists introduced the idea that electrons behave like waves?
Heisenberg & Schrödinger
Give one real-world example of a heterogeneous mixture and explain why.
Soil, oil & water—composition is not uniform.
Compare the particle energy and movement between solids, liquids, and gases.
Solids: low energy, vibrate in place; Liquids: medium energy, slide past; Gases: high energy, move freely
Give an example that illustrates the Law of Multiple Proportions.
CO and CO₂ – both made of C and O, but different mass ratios give different compounds.
Describe one way Bohr’s model of the atom improved on Rutherford’s.
Bohr showed electrons orbit in fixed energy levels rather than randomly around the nucleus.
Explain how the quantum mechanical model differs from Bohr’s orbit model.
Electrons are in probability clouds/orbitals, not fixed orbits.