Atomic Theory

Question 1

Guiding Questions

Answer 1

What are the parts that make up an atom?
What is atomic theory?
What evidence supports the modern model of the atom?

Question 2

Atom

Answer 2

A particle of matter that uniquely defines a chemical element

Question 3

Electron

Answer 3

A stable subatomic particle with a charge of negative electricity, found in all atoms and acting as the primary carrier of electricity in solids

Question 4

Nucleus

Answer 4

The central and most important part of an object, movement, or group, forming the basis for its activity and growth

Question 5

Proton

Answer 5

A stable subatomic particle occurring in all atomic nuclei, with a positive electric charge equal in magnitude to that of an electron, but of opposite sign

Question 6

Neutron

Answer 6

A subatomic particle of about the same mass as a proton but without an electric charge, present in all atomic nuclei except those of ordinary hydrogen

Question 7

Atomic Number

Answer 7

The number of protons in the nucleus of an atom, which determines the chemical properties of an element and its place in the periodic table

Question 8

Isotope

Answer 8

Each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties; in particular, a radioactive form of an element

Question 9

Mass Number

Answer 9

The total number of protons and neutrons in a nucleus

Question 10

Nanowhiskers

Answer 10

tiny threads of carbon or silver that measure about 10 nanometers (1nm = 0.000000001m)

Question 11

What do nanowhiskers have to do with atoms?

Answer 11

Both atoms and nanowhiskers are so small it’s hard to imagine, yet nanowhiskers are still 10x bigger than atoms

Question 12

Scientists have always tried to find the smallest bits of matter that exist

Answer 12

Now they know that even atoms themselves are constructed from smaller particles

Question 13

What is an atom?

Answer 13

An atom is the smallest particle that still can be considered an element

Question 14

Why are atoms so difficult to study?

Answer 14

Because they’re so tiny

Question 15

When did atomic theory start to grow

Answer 15

Atomic Theory began to grow in the 1600s as more scientists began to experiment with atoms

Question 16

Who was John Dalton?

Answer 16

John Dalton, an English chemist, created his own theory which became very popular

Question 17

Dalton’s Atomic Theory

Answer 17

1. All elements consist of atoms that cannot be divided.
2. All atoms of the same element are exactly alike and have the same mass. Atoms of
   different elements are different and have different masses.
3. An atom of one element cannot be changed into an atom of a different element by a
   chemical reaction.
4. Compounds are formed when atoms of more than one element combine in a specific
   ratio.

Question 18

Why might a theory change over time?

Answer 18

New evidence and perspective emerges

Question 19

What major change was made to Dalton’s theory?

Answer 19

Part two of Dalton’s theory had to be modified after mass spectrometry experiments demonstrated that atoms of the same element can have different masses because the number of neutrons can vary for different isotopes of the same element

Question 20

Thomson’s atomic model

Answer 20

Discovered that atoms contain negatively charged particles (electrons). Also reasoned atoms must contain some sort of positive charge (protons).

Question 21

Rutherford’s atomic model

Answer 21

Using his model, concluded that the atom is mostly empty space but has a dense, positive charge at its center.

Question 22

Bohr’s atomic model

Answer 22

Suggested that electrons move only in specific orbits around an atom’s nucleus
(like a solar system).

Question 23

Cloud’s atomic model

Answer 23

Came about in the 1920s and proved Bohr’s theory wrong. Instead electrons
move rapidly within a cloud-like region around the nucleus.

Question 24

How do later atomic theories differ from Dalton’s atomic theory?

Answer 24

Dalton says atoms of different elements differ in size and mass, whereas the modern theory says they differ in average mass

Question 25

In 1932, which English scientist proved that neutrons exist in the nucleus of an atom.

Answer 25

James Chadwick

Question 26

Neutrons, protons, and electrons are known as what?

Answer 26

Subatomic particles

Question 27

A subatomic particle is…

Answer 27

Any particle smaller than an atom.

Question 28

Most of an atom is made up of space in which the electrons move…

Answer 28

This space is huge compared to the space in which the nucleus occupies

Question 29

Protons

Answer 29

+1

Question 30

Electrons

Answer 30

-1

Question 31

Neutrons

Answer 31

0

Question 32

If there’s more protons

Answer 32

The atom is positive

Question 33

If there’s more electrons

Answer 33

The atom is negative

Question 34

If there’s equal parts protons and electrons

Answer 34

The atom is neutral

Question 35

When it comes to the masses of particles…

Answer 35

Protons and neutrons are about equal

Question 36

Electrons

Answer 36

Are much smaller

Question 37

It takes about 1,840 electrons to equal

Answer 37

The mass of one proton or neutron

Question 38

Scientists normally measure atoms using

Answer 38

Atomic mass units

Question 39

What can atoms tell us about elements?

Answer 39

The number of protons in the nucleus of an atom is the atomic number of that atom’s element

Question 40

The definition of an element is based

Answer 40

On its atomic number

Question 41

Every oxygen atom has 8 protons, so…

Answer 41

The atomic number of oxygen is 8

Question 42

Atoms with the same number of protons and different number of neutrons are called

Answer 42

Isotopes

Question 43

An isotope is identified by its mass number

Answer 43

Which is the sum of the protons and neutrons in the atom

Question 44

The most common isotope of oxygen has a mass number of

Answer 44

16

Question 45

Why do you think the mass number only includes the numbers of protons and neutrons?

Answer 45

The mass of the electrons is too small to affect the overall mass