Atomic concepts
 

1.Compared to the charge and mass of a proton, an electron has:
the same charge and a smaller mass
the same charge and the same mass
an opposite charge and a smaller mass
an opposite charge and the same mass
Correct Answer Number: 3

Explanation: Protons are positively charged and have a mass of 1.00720 amu; electrons are negatively charged and have a mass of 0.00055 amu.

2. When alpha particles are used to bombard gold foil, most of the alpha particles pass through undeflected. This result indicates that most of the volume of a gold atom consists of ____.:
deuterons
neutrons
protons
unoccupied space
Correct Answer Number: 4

Explanation: Because most of the particles do not hit anything (pass right through), one can infer the atom is mostly empty space.

3.A proton has approximately the same mass as:
a neutron
an alpha particle
a beta particle
an electron
Correct Answer Number: 1

Explanation: A proton has the same mass as a neutron. An electron has the same mass as a beta particle. An alpha particle has a mass of 4: two protons plus two neutrons

4.When electrons in an atom in an excited state fall to lower energy levels, energy is:
absorbed, only
released, only
neither released nor absorbed
both released and absorbed
Correct Answer Number: 2

5.Which symbols represent atoms that are isotopes?
C-14 and N-14
O-16 and O-18
I-131 and I-131
Rn-222 and Ra-222
Correct Answer Number: 2

Explanation: Isotopes are atoms of the same element (same atomic number) but with a different number of neutrons (different atomic mass). Only choice 2 is correct. Choice 1: C and N are not the same elements. Choice 3: both are the same element but there is no difference in mass. Therefore, they are not isotopes. Choice 4: not the same elements.

6.Which element's ionic radius is smaller than its atomic radius?
neon
nitrogen
sodium
sulfur
Correct Answer Number: 3

Explanation: Elements that lose electrons form positive ions that are smaller than atoms of the same element. Therefore the ionic radius of these ions is smaller than its atomic radius. Only choice 3, sodium, is a metal that will lose electrons. Neon is stable and will neither lose nor gain electrons. N and S will tend to gain electrons, each having a larger ionic radius than atomic radius.

7.Which atom contains exactly 15 protons?
P-32
S-32
O-15
N-15
Correct Answer Number: 1

Explanation: An atom with 15 protons also has an atomic number of 15.