Chemistry Multiple-Choice Practice

Who is the scientist that created the Bohr model?

Niels Bohr

Details on Protons

Positive charge, ~1 amu, in nucleus, atomic number = protons.

Details on Neutrons

Neutral charge, ~1 amu, in nucleus, number varies (isotopes).

Details on Electrons

Negative charge, no mass, orbitals around nucleus.

What are valence electrons?

Number of electrons in outermost shell.

What is the 11th Electron Shell’s Capacity (using 2n² rule)?

242 electrons.

How do Ions form?

Ion = gain/lose electrons; cation = loses, anion = gains.

When do atoms have more protons than electrons?

In cations.

What causes radioactivity in atoms?

When an unstable nucleus emits radiation to stabilize.

What is half-life?

Time for half of radioactive atoms to decay.

What makes a stable nucleus?

Stability depends on balance of protons & neutrons.

How are isotopes different from normal atoms?

Different amount of protons.

What is relative abundance?

The percent of each isotope in nature.

What happens in beta decay?

A neutron converts into a proton and an electron (beta particle). The electron is emitted, the atomic number increases by 1, and the mass number stays the same.

What happens in alpha decay?

The nucleus emits two protons and two neutrons (an alpha particle, a.k.a. helium nucleus). The atomic number decreases by 2 and the mass number decreases by 4.

Why and how do atoms become ions.

Atoms become ions when they gain or lose electrons, to achieve a more stable electron configuration.

What is the atomic number?

The number of protons in the nucleus of an atom.

Whats the difference between mass number and average atomic mass?

Mass number is the total number of protons and neutrons in a single atom, while average atomic mass is the weighted average of all naturally occurring isotopes of that element.