Structure of the Atom and Isotopes

Atomic Structure

What are the three main subatomic particles?

Protons, neutrons and electrons.

Where are protons found in an atom?

In the nucleus.

Where are neutrons found in an atom?

In the nucleus.

Where are electrons found in an atom?

In energy levels, or quantum shells, surrounding the nucleus.

What is the relative mass of a proton?

1.

What is the relative mass of a neutron?

1.

What is the relative mass of an electron?

1/1840.

What is the relative charge of a proton?

+1.

What is the relative charge of a neutron?

0.

What is the relative charge of an electron?

−1.

Which subatomic particles account for most of the mass of an atom?

Protons and neutrons.

Why should you not say that an electron has zero mass?

An electron has a very small relative mass of about 1/1840, not zero.

What is the nucleus?

The small central region of an atom containing protons and neutrons.

Where is most of the mass of an atom concentrated?

In the nucleus.

What are quantum shells?

Well-defined energy levels surrounding the nucleus in which electrons are found.

Who discovered the electron?

J. J. Thomson in 1897.

Who discovered the proton?

Ernest Rutherford.

Who discovered the neutron?

James Chadwick in 1932.

What is atomic number?

The number of protons in the nucleus of an atom.

What symbol is used for atomic number?

Z.

How can you determine the number of protons from the atomic number?

Number of protons = atomic number.

Do all atoms of the same element have the same atomic number?

Yes, because they have the same number of protons.

What is mass number?

The total number of protons and neutrons in the nucleus of an atom.

How do you calculate mass number?

Mass number = number of protons + number of neutrons.

How do you calculate the number of neutrons?

Number of neutrons = mass number − atomic number.

In isotope notation, where is the mass number written?

At the top left of the element symbol.

In isotope notation, where is the atomic number written?

At the bottom left of the element symbol.

What is the relationship between protons and electrons in a neutral atom?

The number of electrons equals the number of protons.

Why is an atom electrically neutral?

It contains equal numbers of positively charged protons and negatively charged electrons.

How is a positive ion formed?

When an atom loses one or more electrons.

How is a negative ion formed?

When an atom gains one or more electrons.

How can you identify a positive ion from its numbers of protons and electrons?

It has more protons than electrons.

How can you identify a negative ion from its numbers of protons and electrons?

It has more electrons than protons.

How do you calculate the charge of an ion?

Charge = number of protons − number of electrons.

What is an isotope?

An atom of the same element with the same atomic number but a different mass number.

What do isotopes of the same element have in common?

The same number of protons.

What is different between isotopes of the same element?

They have different numbers of neutrons and therefore different mass numbers.

Why do isotopes have different masses?

They contain different numbers of neutrons.

Why do isotopes of the same element have the same chemical properties?

They have identical electronic configurations.

What are two common isotopes of carbon?

Carbon-12 and carbon-13.

How many protons does carbon-12 have?

6.

How many neutrons does carbon-12 have?

12 − 6 = 6.

How many electrons does a neutral carbon-12 atom have?

6.

How many protons does carbon-13 have?

6.

How many neutrons does carbon-13 have?

13 − 6 = 7.

Why is carbon-13 heavier than carbon-12?

Carbon-13 contains one more neutron.

What are two isotopes of chlorine?

Chlorine-35 and chlorine-37.

How many protons are in chlorine-35?

17.

How many neutrons are in chlorine-35?

35 − 17 = 18.

How many electrons are in a neutral chlorine-35 atom?

17.

How many protons are in chlorine-37?

17.

How many neutrons are in chlorine-37?

37 − 17 = 20.

How many electrons are in a neutral chlorine-37 atom?

17.

Why are chlorine-35 and chlorine-37 isotopes?

They both have 17 protons but have different numbers of neutrons.

What determines which element an atom is?

Its number of protons, or atomic number.

Can two different elements have the same atomic number?

No.

Can isotopes have the same mass number?

Not if they are isotopes of the same element; isotopes have different mass numbers.

Does changing the number of neutrons change the element?

No, it produces a different isotope of the same element.

Does changing the number of protons change the element?

Yes.

An atom has 12 protons and 13 neutrons. What is its mass number?

25.

An atom has mass number 24 and atomic number 12. How many neutrons does it contain?

12.

An atom has 17 protons and 18 electrons. What is its charge?

−1.

An atom has 11 protons and 10 electrons. What is its charge?

+1.

An atom has 35 protons and 36 electrons. What is its charge?

−1.

An atom has 19 protons and 18 electrons. What is its charge?

+1.

What three pieces of information can atomic number and mass number help you determine?

The numbers of protons, neutrons and electrons in an atom or ion.