Atomic models & the periodic table

Question 1

What is an atom?

Answer 1

An atom is the smallest unit of ordinary matter that forms a chemical element.

Question 2

What is an element?

Answer 2

An element is a pure substance (only one type) that cannot be broken down into simpler/smaller units using chemical reactions.

Question 3

Element vs atom example

Answer 3

For example, water (H2O) is composed of 2 hydrogen atoms and one oxygen atom.
An element is a collection of atoms of the same type

Question 4

Dalton (DESCRIBE)

Answer 4

Solid sphere model, 1803

Question 5

Thomson (DESCRIBE)

Answer 5

Plum pudding model, 1897

Question 6

Rutherford (DESCRIBE)

Answer 6

Nuclear model, 1911

Question 7

Planetary model (DESCRIBE)

Answer 7

Bohr 1913

Question 8

Simplified atomic model (DESCRIBE)

Answer 8

Chadwick, 1932

Question 9

Solid sphere model

Answer 9

John Dalton described atoms as tiny particles that could not be divided.
Dalton had no idea of the size of atoms or how they were constructed. His model was called the Solid Sphere Model.

Question 10

From who did Dalton take his idea?

Answer 10

He took this basic idea from Democritus, who used the word “atomos” to describe the smallest possible piece of matter.

Question 11

Describe J.J Thomson’s experiment

Answer 11

Thomson experimented with cathode ray tubes, cutting edge technology of his time.
Strong potential differences (voltage) between two metal plates cause electrons to be ejected from the cathode plate.Thomson was able to deflect the electrons using electric fields.

Question 12

What did J.J. Thomson conclude from his experiment?

Answer 12

Thomson was able to deflect the electrons using electric fields, demonstrating that the particles had negative charge.

Question 13

How did Thomson modify Dalton’s model?

Answer 13

Thomson modified Dalton’s model to better explain his findings.
Atoms must contain smaller negative particles, electrons.
Electrons can be removed from atoms.

Question 14

What was the problem with Thomson’s model?

Answer 14

His problem was that he could not find the positive charge in the atom that would balance the charge of the negative electrons.

Question 15

Describe the developments in technology that were rapid in 1908 (Ernest Rutherford).

Answer 15

Following cathode rays, scientists quickly discovered how to produce and use many kinds of radiation: x-rays, rays made of alpha, beta, gamma particles.
Scientists experimented with alpha particles, which are much bigger than electrons and have a positive charge.

Question 16

Describe the gold foil experiment

Answer 16

Rutherford expected most of the alpha particles to pass through the gold foil. It was only 160 atoms thin (0.00004 cm)!
(average human hair = 0.007 cm)
This was mostly true, but every now and then an alpha particle would bounce back, like it hit something much bigger with a strong positive charge.
(remember: like charges repel, similarly to magnetic repulsion)

Question 17

What is Rutherford’s theory?

Answer 17

Rutherford’s theory is that the nucleus is very dense, and has a positive charge. The electrons revolve around of the nucleus.

His theory was that the atom looked like the solar system with the sun in the middle and the planets revolving around it. His model is called the Planetary Model.

Question 18

What was the problem with Rutherford’s model?

Answer 18

But many scientists had trouble understanding how the electrons could remain circling around the nucleus.
Since positive and negative charges attract, shouldn’t the electrons eventually crash into the nucleus?
The Collapse of the Atom!

Question 19

By 1913, scientists knew that …

Answer 19

light was related to the movement of electrons.
They were able to make light by exciting electrons in gas molecules with electric potential (voltage).
Using a prism, light of different wavelength (color) is refracted and viewed separately.

Question 20

What was Bohr able to understand?

Answer 20

Bohr was able to understand why only certain frequencies of light were being emitted.
Remember, light is emitted from a moving electron.
Since only very specific types (energies) of light were being emitted, the electrons had to be moving in very specific ways too.

Question 21

What is wrong with Bohr’s model?

Answer 21

Bohr’s is still incomplete. Remember how charges react: unlike charges attract (+ / -); like charges repel (+/+) (-/-).

Question 22

What did James Chadwick discover?

Answer 22

Building on the work of colleagues across the world, Chadwick discovered the neutron in 1932.
Scientists had discovered a new type of radiation particle that was very energetic, like alpha particles, but it did not carry a charge.

Question 23

What did the neutron explain?

Answer 23

The neutron eventually helped us understand why the nucleus doesn’t repel itself apart.
Neutrons allow the Strong Nuclear Force to hold the protons in the nucleus together.

Question 24

Quickly describe Chadwick’s experiment

Answer 24

Performing this experiment on paraffin and gases, Chadwick was able to determine that the new radiation was a neutral (no charge) particle about the same mass as a proton.

Question 25

Describe Neil’s Bohr experiment

Question 26

Cr

Answer 26

Chromium

Question 27

Fe

Answer 27

Iron

Question 28

Ni

Answer 28

Nickel

Question 29

Cu

Answer 29

Copper

Question 30

Zn

Answer 30

Zinc

Question 31

Br

Answer 31

Bromine

Question 32

I

Answer 32

Iodine

Question 33

Ag

Answer 33

Silver

Question 34

Hg

Answer 34

Mercury

Question 35

Pb

Answer 35

Lead

Question 36

Valence electron

Answer 36

Valence means the outermost layer/shell of an atom.
Valence electrons are the electrons in the outermost layer/shell of an atom.

Question 37

Columns (Different groups)

Answer 37

There are 2 types of groups on the periodic table: A and B
Each element of the same group in section A has the same number of valence electrons
The elements in section B are transition metals. These elements can have different numbers of valence electrons.

Question 38

Families (how many + similiarities)

Answer 38

Like human members of a family, atoms of the same family have similar appearance and behaviour.
The reason for this is because atoms of the same group (column) have the same number of Valence Electrons (group A only).
Valence electrons are largely responsible for how an atom behaves and reacts. (remember the clothing analogy)
There are 4 special groups in the periodic table that make up these families.

Question 39

Group 1A

Answer 39

: Alkali Metals

Question 40

Group 2A

Answer 40

Alkaline Earth Metals

Question 41

Group 7A:

Answer 41

Halogens (gases)

Question 42

Group 8A:

Answer 42

Noble Gases

Question 43

Alkali metals characteristics

Answer 43

Soft
HIGHLY reactive - for this reason they are not found in their pure state naturally.
In their pure state, they must be stored in oil

Question 44

Alkaline Earth Metals properties

Answer 44

Highly malleable (can be bent into shapes)
Very reactive - but will not react on contact with the air (like the alkali metals)
They can be found in their pure state in nature

Question 45

Transition metals characteristics

Answer 45

Harder metals - all solid at room temperature EXCEPT Hg (mercury)

Question 46

Halogens characteristics

Answer 46

Very reactive with metals to form salts
Powerful disinfectants (think of chlorine in pools)

Question 47

Noble gases characteristics

Answer 47

Very stable - non reactive
They are found in their pure state in nature

Question 48

Periods: rows

Answer 48

Each element of the same period will have the same number of electron shells

Question 49

Octect rule

Answer 49

Since we are only investigating the structure of the first 20 atoms, we simplify by using the octet rule.
Octet Rule:
The first electron shell (1st row) may contain a maximum of 2 electrons
The second, third and fourth shells (2nd, 3rd and 4th rows) may contain a maximum of 8 electrons.

Question 50

Metals

Answer 50

Metals are located to the left of the staircase.
good conductors of electricity and heat, they are ductile, malleable and often shiny, they are usually solid at room temperature and react with acid.
Metals tend to give away its valence electrons in presence of nonmetals

Question 51

Non-metals:

Answer 51

Non-metals are located to the right of the staircase
Poor conductors of electricity and heat, many are gases at room temperature. when solid, they can easily be reduced to powder.
Nonmetals tend to accept valence electrons in presence of metals to reach a full octet.

Question 52

Metalloids:

Answer 52

Located on the staircase
The properties of these elements vary depending on conditions

Question 53

Atomic number

Answer 53

The whole number found next to each element symbol. These numbers are in order: 1 is Hydrogen (top left) and increase from left to right.
This number represents the number or protons in the nucleus of that element.

Question 54

Chemical Symbol

Answer 54

Symbol used to represent each element. The first letter will always be a capital letter. If there is a second letter (i.e. Mg) it will be lowercase.

Question 55

(Relative) Atomic mass:

Answer 55

the mass of an atom (determined by comparing it to carbon). We will revisit this in our chemistry unit!

Question 56

Mass number

Answer 56

Round the relative atomic mass to a whole number. Indicates the sum of protons and neutrons in an atom.

Question 57

How to calculate the number of neutrons

Answer 57

The atomic number (6) tells us the # of protons in the nucleus.
The mass number (atomic mass(12.01), rounded (12)) tells us the total # of particles in the nucleus (protons + neutrons).
In order to know the # of neutrons:
subtract the atomic number from the mass number.

neutrons = (Mass Number) - (Atomic Number)

Question 58

A Z E Notation

Answer 58

An effective way to keep track of mass, protons (and neutrons).
The upper number (A) is the mass number of the atom (always larger)
The lower number (Z) is the atomic number of the atom (always smaller)
A = Z + N, N = A - Z

Question 59

Rutherford-Bohr Atomic Model
characteristics

Answer 59

Nucleus in the center (composed of protons)
A neutral atom will have the same number of protons as electrons.
Electrons travel around the nucleus on specific paths. These paths are called energy levels
Not every path can hold the same amount of electrons.
For now the rule is:
1st shell: 2 electron,
2nd shell: 8 electrons,
3rd shell: 8 electrons

Question 60

Simplified Atomic Model
characteristics

Answer 60

This new model adds information about the nucleus.

Like the Rutherford-Bohr model, we state the number of positive protons in the nucleus.

We also state the number of neutral neutrons in the nucleus.

Electron shell orbits are represented by semi-circles, and the number of electrons in the shell written below.

Question 61

Valence Electrons/Valence Shell

Answer 61

When understanding atoms and the electrons of an atom, we often need to think of Valence.
Valence means the outermost layer/shell of an atom.
Valence electrons are the electrons in the outermost layer/shell of an atom.

Question 62

Why are valence electrons important?

Answer 62

When one atom encounters another atom, they may interact.
The interaction usually involved Valence Electrons, because they are the outermost electrons.
The inner electrons are essentially “hidden” by the valence shell.

Question 63

Lewis notation

Answer 63

Lewis notation is a simple representation of an element’s outer electron shell (valence shell).
Key components:
The element’s symbol (i.e. lithium → Li, fluorine → F)
Dots representing the number of valence electrons
Always fill single dots on each side before doubling

Question 64

Isotopes

Answer 64

Isotope: atoms of the same element with different numbers of neutrons.
Because they contain different numbers of neutrons, isotopes have different atomic masses.

Question 65

How is the average atomic mass calculated

Answer 65

The average atomic mass of an element is calculated by taking the weighted average masses of the element’s naturally occurring isotopes.