Ch 3 Review

In Rutherford’s Gold Foil experiment, since most particles fired at metal foil pass through the foil, it may be concluded that . . .

• atoms are mostly empty space

• atoms contain no charged particles

• electrons form the nucleus

• atoms cannot be divided into smaller particles

Answer explanation

Because most went through without hitting anything.

In Rutherford’s Gold Foil experiment, since few positively-charged particles bounce back from the metal foil, it may be concluded that . . .

• atoms cannot be divided into smaller particles

• electrons make up the center of the atoms

• an atom is positively charged

• an atom contains a small, dense, positively charged nucleus

Answer explanation

Few hit so the nucleus must be tiny. Positively charged particles were repelled by the positively charged nucleus. Dense because they bounced back.

The nucleus of the atom contains nearly all the atom's mass.

• True

• False

Answer explanation

That's where all the big particles are.

The nucleus of the atom takes up nearly all the space in the atom.

• True

• False

Answer explanation

Nope. The nucleus is tiny. If it was the size of a basketball, the average electron would be 10 miles away. Tiny nucleus.

An atom is electrically neutral because . . .

• neutrons balance the protons and electrons

• nuclear forces equalize the charges

• the number of protons and electrons is equal

• the number of protons and neutrons is equal

Answer explanation

Positively charged protons = the negatively charged electrons. That balances out to be neutral.

The smallest unit of an element that is still that element is the ___.

• proton

• electron

• nucleus

• atom

Answer explanation

Anything smaller than that is no longer unique to a certain element.

What defines an atom to be an atom of gold?

• It has 79 protons

• It has 79 electrons

• It has 118 neutrons

• It has a mass number of 197

Answer explanation

Every element has a unique number of protons in the atom. Change the number of protons and you change it into a different element.

Isotopes are atoms of the same element that have different ___.

• only the number of electrons

• only the number of neutrons

• only the mass numbers

• both number of neutrons and mass numbers

Answer explanation

Different number of neutrons but that then changes the mass number as well.

The mass number of an isotope tells ___.

• number protons + electrons

• number protons + neutrons

• number neutrons + electrons

• number neutrons X 2

Answer explanation

Don't confuse that with the atomic number.

Can the mass number for an isotope be found on the periodic table?

• Yes

• No

Answer explanation

Nope. The average atomic mass is the weighted average of all the naturally occurring isotopes for an element. The mass number applies to only one isotope. In fact, two different elements can have isotopes with the same mass number.