Inside Atoms

Inside an Atom

Theories about the shape and structure of atoms ahve developed and changed over the last 200 years. but some ideas are well understood.

The central core of the atom is called the nucleus.

​

​An atom consists of a nucleus surrounded by one or more electrons.

The small particles inside the nucleus are called protons and neutrons. The energetic particles moving in all directions around the nucleus are electrons.

​

​An atom consists of a nucleus surrounded by one or more electrons.

Protons carry a positive electrical charge (+). Electrons carry a negative charge (-). Neutrons are considered neutral because they carry no electrical charge.

​An atom consists of a nucleus surrounded by one or more electrons.

​+

-

Protons and neutrons have approximately the same mass.
One proton is about 2,000 times as massive as one electron.

​An atom consists of a nucleus surrounded by one or more electrons.

Multiple Choice

the central core of the atom which makes up most of the atom's mass

• electron

• neutron

• nucleus

• proton

Multiple Choice

a particle inside an atom that carries a positive electrical charge

• electron

• neutron

• nucleus

• proton

Multiple Choice

a particle that rapidly moves around the outside of

the nucleus and carries a negative charge

• electron

• neutron

• nucleus

• proton

Multiple Choice

a particle inside an atom that does not carry an electrical charge

• electron

• neutron

• nucleus

• proton

As a result, the total positive charge and total negative charge balance each other, making a neutral atom. The number of neutrons in an atom may be the same as the number of protons, but not always.

In an atom, the number of protons equals the number of electrons.

Multiple Choice

In a stable atom, how are the number of protons and electrons determined?

• They are equal in number.

• Protons are twice the number of electrons.

• Electrons are twice the number of protons.

• Protons and electrons have no correlation in a stable form.

Multiple Choice

An atom of Hydrogen has 1 proton. How many electrons does it have?

• 1

• 2

• 4

• 0

Multiple Choice

An atom of Carbon has 6 electrons. How many protons does it have?

• 2

• 3

• 6

• 12

Electrons move so rapidly in the space around the nucleus that it is impossible to know exactly where any electron is at a particular time.

You can think of the space around the nucleus of an atom as a spherical cloud of negatively charged electrons. This space is extremely large compared to the space occupied by the nucleus.

Only the electrons that are the farthest from the nucleus are involved in bonding. They are called valence electrons. Atoms react with each other based on how many valence electrons each has.

The electrons in an atom aren't all the same distance away from the nucleus.

One way to show the number of valence electrons is an electron dot diagram.

Electron dot diagram

It includes the symbol for an element surrounded by dots. Each dot stands for one valence electron.

A neutral atom never has more than eight valence electrons.

When atoms form bonds, they may gain or share electrons, leading to an increase to a total number of eight. Or atoms may lose their valence electrons, ending up with no valence electrons. Chemists say that atoms that undergo these changes become more chemically stable.

​A chemical bond forms between two atoms when valence electrons move between them. Electrons may be transferred from one atom to another, or they may be shared between the atoms.

Multiple Choice

What kind of diagram, seen here, is typically used to represent the valence electrons of an atom in chemistry?

• Lewis structure diagram

• Bohr diagram

• Electron dot diagram

• Venn diagram

Multiple Choice

In an electron dot diagram, what do the dots typically represent?

• Atomic nucleus

• Inner shell electrons

• Valence electrons

• Protons and neutrons

Multiple Choice

Which element shown is the most chemically stable?

• Li

• C

• F

• Ne

Multiple Choice

A neutral atom of sodium has 11 protons. Use this information to determine the total

number of electrons that are in a sodium atom.

• 5

• 11

• 12

• 22

Multiple Choice

Which subatomic particles make up most of the mass of an atom?

• Electrons and positrons

• Protons and electrons

• Protons and neutrons

• Neutrons and electrons