Atomic Theory and Atomic Structure (Video Notes)

A set of practice flashcards covering Dalton's atomic theory, isotopes, fundamental laws, atomic models (Plum Pudding, Bohr, Rutherford), and calculations involving atomic number, mass number, and neutrons.

Who formulated the atomic theory that matter is composed of minute particles?

John Dalton.

How many postulates are in Dalton's atomic theory?

Four postulates.

What is the 1st postulate of Dalton's atomic theory?

Matter is composed of small, indivisible particles called atoms.

What is the 2nd postulate of Dalton's atomic theory?

Each element has unique atoms; atoms of the same element are identical.

What is the 3rd postulate of Dalton's atomic theory?

Compounds are formed when atoms of different elements combine in whole-number ratios.

What is the 4th postulate of Dalton's atomic theory?

In a chemical reaction, atoms are rearranged but not changed.

What are isotopes?

Forms of an element with different numbers of neutrons; same atomic number (Z) and protons; different atomic masses.

What does the Law of Mass Conservation state?

In a chemical reaction, the total mass of the reactants equals the total mass of the products.

Name two other fundamental laws related to compounds.

Law of definite proportions and Law of multiple proportions.

What does the Law of Definite Proportions state?

A pure substance is composed of the same elements in the same proportions by mass, regardless of the source.

What does the Law of Multiple Proportions state?

When two elements form more than one compound, the mass of one element that combines with a fixed mass of the other is always in a whole-number ratio.

What is the Plum Pudding model and who proposed it?

A positively charged blob with negatively charged electrons spread through it; proposed by J.J. Thomson.

What was the aim of the Plum Pudding model?

To explain how electrons could exist within an atom without giving the atom an overall charge.

What did Rutherford's Gold Foil experiment demonstrate?

Atoms are mostly empty and contain a tiny, dense, positively charged nucleus; some alpha particles were deflected at large angles.

Who proposed Bohr's model?

Niels Bohr.

What is Bohr's model based on?

Electrons occupy fixed orbits with quantized energies; energy increases with distance from the nucleus.

Which subatomic particle is positively charged and what determines its number?

Protons; their number is the atomic number Z.

Which subatomic particle is negatively charged and what determines its number?

Electrons; in neutral atoms, their number equals the atomic number Z.

What is the neutron's charge and its role?

Neutral; contributes to mass; involved in determining the mass number A.

What does the Bohr model’s appearance resemble?

A solar-system-like arrangement with electrons in fixed orbits around the nucleus.

What determines the identity of an element?

The number of protons (atomic number Z).

What is meant by a neutral atom?

An atom with equal numbers of protons and electrons (p+ = e−).

What is Atomic Number (Z)?

Number of protons (and, in a neutral atom, electrons).

What is Mass Number (A)?

Total number of protons and neutrons.

How do you calculate the number of neutrons (n) if you know A and Z?

n = A − Z (since Z equals the number of protons and, in a neutral atom, electrons).

For gold (Au) with A = 197 and Z = 79, how many neutrons are present?

n = 197 − 79 = 118.

For cobalt (Co) with Z = 27 and A = 59, how many neutrons are present?

n = 59 − 27 = 32.