The Nuclear Atom

Question 1

The nucleus of an atom contains:

Accepted Answer

protons and neutrons — The nucleus is made of protons and neutrons; electrons orbit outside it.

Question 2

The particle with no electric charge is the:

Accepted Answer

neutron — A neutron is neutral; a proton is +1 and an electron is &minus;1.

Question 3

An atom has 6 protons and 8 neutrons. Its nucleon number is:

Accepted Answer

14 — Nucleon number = protons + neutrons = 6 + 8 = 14.

Question 4

The proton number of an atom:

Accepted Answer

defines which element it is — The proton (atomic) number identifies the element.

Question 5

Isotopes of an element have the same number of:

Accepted Answer

protons but different neutrons — Isotopes share the proton number but differ in neutron number.

Question 6

How many neutrons are in an atom of 146C?

Accepted Answer

8 — Neutrons = nucleon number &minus; proton number = 14 &minus; 6 = 8.

Question 7

Rutherford's alpha-scattering experiment showed that an atom:

Accepted Answer

is mostly empty space with a small dense nucleus — Most alpha particles passed straight through, showing the atom is mostly empty with a tiny nucleus.

Question 8

Compared with a proton, the mass of an electron is:

Accepted Answer

negligible (about 1/1840) — An electron has roughly 1/1840 of a proton's mass, so it is treated as negligible.

Question 9

In a neutral atom, the number of electrons equals the number of:

Accepted Answer

protons — A neutral atom has equal numbers of protons and electrons, so the charges cancel.

Question 10

Almost all of the mass of an atom is found in the:

Accepted Answer

nucleus — Protons and neutrons in the nucleus account for nearly all the atom's mass.

Particle	Charge	Relative mass
Proton	+1	1
Neutron	0	1
Electron	−1	about 1/1840 (negligible)

Particles and charges

Isotopes and notation