Periodic table & atom structure review (STAAR)

The atomic # of krypton is 26. If the mass number of a krypton atoms is 84, which table shows the number of subatomic particles inside and outside the nucleus of the krypton atom?

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Answer explanation

Where is everything located?

The nucleus is in the middle (yellow circle). The nucleus contains neutrons and protons. Outside the nucleus, we have the green electrons buzzing around.

To get how many of each there are,

Remember:

Atomic # (info in periodic table) = protons = electrons. They are all the same number! (in this case 36)

Neutrons = mass - atomic #.

So, let's put it all together:

Krypton's atomic # = 36.

Protons= 36 (same as atomic #)

Neutrons= 84 (mass) - 36 (atomic #) = 48

Electrons=36 (same as atomic #)

So how many inside and outside?

INSIDE: # of particles inside the nucleus (protons + neutrons) = 36 (protons) + 48 (neutrons) = 84

OUTSIDE= # of particles outside the nucleus (electrons only) = 36

Which statement accurately describes the atoms of a specific element?

• F

• G

• H

• J

Answer explanation

Remember:

Protons = atomic #

Electrons = atomic #

Neutrons = mass # - atomic #

Zinc, atomic # = 30 according to the periodic table.

Because of this, Zinc will have 30 protons inside the nucleus, and 30 electrons outside the nucleus.

Simple!

Which statement correctly describes the location and charge of the electrons in an atom?

• F

• G

• H

• J

Answer explanation

Electrons (-) are negative

Protons (+) are positive

Neutrons ( ) are neutral/no charge

As seen in the picture, protons and neutrons are inside the nucleus. Only electrons are orbiting on the outside.

Which statement correctly describes the location and charge of the electrons in an atom?

• F

• G

• H

• J

Answer explanation

Electrons (-) are negative

Protons (+) are positive

Neutrons ( ) are neutral/no charge

As seen in the picture, protons and neutrons are inside the nucleus. Only electrons are orbiting on the outside.

What is the total # of protons, neutrons, and electrons in a cadmium, Cd, atom that has a mass # of 112?

Answer explanation

In the periodic table, Cadmium's atomic # = 48.

So,

Protons = atomic # = 48

Electrons = atomic # = 48

Neutrons = mass # (112) - atomic # (48) = 64

What is the difference between the number of electrons in an atom of selenium, Se, and the number of electrons in an atom of aluminum, Al?

Answer explanation

In the periodic table, selenium's atomic # = 34.

aluminum's atomic # = 13

Remember:

Electrons = atomic #

Calculate the difference:

selenium (34) - aluminum (13) = 21

Read the question in the image.

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• B

• C

• D

Answer explanation

Hafnium, Hf has an atomic # = 72

Protons = atomic # = 72

neutrons = mass (178) - atomic # (72) = 106

electrons = atomic # = 72

An atom of a certain element has 36 protons, 36 electron, and a mass number of 84. At room temperature this element is a very stable gas. How many neutrons are in this atom?

Answer explanation

Neutrons = mass # - atomic #

Neutrons = mass (84) - atomic #(what is this number?)

Well, the question gives us:

Protons/electrons = atomic # = 36

So,

Neutrons = mass (84) - atomic # (36) = 48

Read the question in the image.

• A

• B

• C

• D

Answer explanation

Read the question in the image.

• A

• B

• C

• D

Answer explanation

Potassium (atomic # = 19)

The mass number given = 39