Unit 2_ The Atom Test Study Guide

Who proposed that matter is made of indivisible particles called 'atomos'?

Democritus

What are the main points of John Dalton's atomic theory?

1. All matter is made of atoms. 2. Atoms of the same element are identical. 3. Atoms cannot be created, divided, or destroyed. 4. Atoms combine in whole-number ratios to form compounds. 5. Chemical reactions rearrange atoms but do not change them into other atoms.

What discovery is J.J. Thomson known for?

Discovering the electron using the cathode ray tube experiment.

What did Ernest Rutherford conclude from the gold foil experiment?

Atoms have a small, dense, positively charged nucleus surrounded by empty space.

What model did Niels Bohr propose about electrons?

Electrons orbit the nucleus in fixed energy levels.

What does the quantum mechanical model developed by Erwin Schrödinger describe?

Electron behavior in probabilistic orbitals instead of fixed paths.

What is an ion?

An atom that has lost or gained electrons.

What is the difference between cations and anions?

Cations are positively charged ions that lose electrons, while anions are negatively charged ions that gain electrons.

Define isotopes.

Atoms of the same element with different numbers of neutrons, changing their atomic mass but not their chemical properties.

What is atomic mass?

Mass of a single atom, calculated as the sum of protons and neutrons.

What is average atomic mass?

Weighted average of all an element’s isotopes.

What are orbitals?

Regions of space where electrons are most likely found.

What are the types of orbitals and their electron capacity?

s-orbital: holds 2 electrons, p-orbital: holds 6 electrons, d-orbital: holds 10 electrons, f-orbital: holds 14 electrons.

What does Hund’s Rule state?

Electrons fill orbitals singly before pairing up.

What happens to electrons during atomic emission?

When electrons absorb energy, they jump to higher energy levels and release energy as light when they fall back down.

What does the hydrogen emission spectrum produce?

Distinct lines of color when excited electrons return to lower energy levels.

How does an electron transition from n=1 to n=2 affect its energy?

An electron absorbing energy jumps from n=1 to n=2, entering an excited state.

What occurs when an electron transitions from n=2 to n=1?

When an electron transitions from n=2 to n=1, it releases energy and emits a photon of specific color.

Year of Democritus

400 BCE

Year of John Dalton

1803

Year of J.J. Thompson

1897

Year of Ernest Rutherford

1911

Year of Bohr

1913

Year of Schrödinger

1926