Physics - ATOMIC STRUCTURE (P4)

Atoms & Isotopes -

What are the three subatomic particles in an atom + their charges?

Proton (+1), neutron (0), electron (-1)

Atoms & Isotopes -

What is the mass of each subatomic particle?

Proton: 1, Neutron: 1, Electron: ~0 (very small)

Atoms & Isotopes -

Define atomic number + mass number.

Atomic number = number of protons

Mass number = protons + neutrons

Atoms & Isotopes -

What is an isotope?

Atoms of the same element w/ the same number of protons but a different number of neutrons.

History of the Atoms -

What did John Dalton suggest about atoms?

That atoms are indivisible spheres.

History of the Atoms -

What was Thomson’s model of the atom called?

The plum pudding model.

History of the Atoms -

What did Rutherford’s alpha scattering experiment show?

That atoms have a small, dense, positively charged nuclues.

History of the Atoms -

What was Bohr’s contribution to the atomic model?

Electrons orbit the nucelus at specific distances (energy levels).

History of the Atoms -

What did James Chadwick discover?

The neutron.

Radioactivity -

What is radioactive decay?

A random process in which unstable atomic nuceli release radiation to become more stable.

Radioactivity -

What are the three types of ionising radiation?

Alpha (α), Beta (β), Gamma (γ)

Radioactivity -

Describe the properties of alpha radiation.

Low penetration (stopped by paper), strongly ionising, consists of 2 protons + 2 neutrons.

Radioactivity -

Describe the properties of beta radiation.

Medium penetration (stopped by aluminium), moderately ionising, consists of a high-speed electron.

Radioactivity -

Describe the properties of gamma radiation.

Highly penetrating (stopped by thick lead), weakly ionising, electromagnetic wave.

Radioactivity -

What is background radiation?

The low level of radiation present all around us from natural + artificial sources.

Nuclear Equations -

What happens in alpha decay?

The nucleus loses 2 protons + 2 neutrons (mass number decreases by 4, atomic number by 2).

Nuclear Equations -

What happens in beta decay?

A neutron turns into a proton + an electron; the electron is emitted (atomic number increases by 1).

Nuclear Equations -

What happens in gamma emission?

No change in mass / atomic number; gamma radiation is emitted from the nucleus.

Nuclear Equations -

Complete this nuclear equation

Uranium -238 undegoes alpha decay the alpha particle is a helium nucleus with the mass number 4 and atomic number 2.

Mass number of Uranium (-238) - mass number of alpha particle = mass number of unknown product

238 - 4 = 234

Atomic number of Uranium (-238) - atomic number of alpha particle = atomic number of unknown product

92 - 2 = 90

Element w/ atomic number 90 is Thorium (Th), so the unkown product is Th (with mass number 234 and atomic number 90).

The balanced nuclear equation - 238/92 U → 234/90 Th + 4/2 a

Half-Life -

What is half-life?

The time it takes for half the radioactive nuceli in a sample to decay.