Atomic Theory and Structure of the Atom Flashcards
Q: When did atomic theory first emerge?
A: Over 2,500 years ago, but strong evidence emerged in the 1800s.
Q: What are the five key points of Dalton’s atomic theory?
- Matter consists of tiny, indivisible atoms.
- Atoms are indestructible in chemical reactions (they only rearrange).
- All atoms of an element are identical in mass and properties.
- Atoms of different elements have different masses and properties.
- Atoms combine in fixed whole-number ratios to form compounds.
Q: Can elements combine in different whole-number ratios? Give an example.
A: Yes. Example:
Sulfur dioxide (SO₂)
Sulfur trioxide (SO₃)
Q: If a compound contains 1.5g of molybdenum and 1g of sulfur, what mass of molybdenum is present in a sample with 2.5g of sulfur?
Original ratio: 3:2 (Mo:S)
New sulfur mass = 2.5g
Solve for Mo: (3/2) × 2.5 = 3.75g
Q: What are the three subatomic particles?
A: Protons, neutrons, and electrons.
Q: What is the Law of Conservation of Mass?
A: Matter cannot be created or destroyed in a chemical reaction; mass in = mass out.
Q: Who proposed the Law of Conservation of Mass?
A: Antoine Lavoisier.
Q: What is the Law of Definite Proportions?
A: Elements in a compound always combine in the same fixed ratio by mass.
Q: Who proposed the Law of Definite Proportions?
A: Joseph Louis Proust.
Q: What happens if elements combine in a non-fixed ratio?
A: A different compound is formed.
Q: Where are protons found and what is their charge?
A: In the nucleus; positive charge.
Q: Where are neutrons found and what is their charge?
A: In the nucleus; neutral charge.
Q: Where are electrons found and what is their charge?
A: In the electron cloud; negative charge.
Q: What is the relative mass of electrons compared to protons?
A: About 1/1000th of a proton’s mass.
Q: What percentage of an atom’s volume is occupied by the nucleus?
A: Less than 0.1%.
Define Isotopes
Atoms of element with the same number of protons but different number of neutrons, hence different mass number
