Lecture 3: Phases, Properties, Particles, and the Periodic Table

Course

Unit 1

Chapter 1

General Chemistry

Molecular Structure and Properties

Introduction

This lecture is part of the MEEP curriculum on General Chemistry. Information about Project MEEP and other General Chemistry lectures are available below.

Project MEEP

General Chemistry

Recommended Time: 1.5 Hours

Lecture Preview

What are phases of matter and how are they different from each other?
What are physical and chemical properties and how are they different from each other?
What are the particles in an atom? How are they important?
What are some properties listed on the periodic table and how are they important?

Lecture Content (Part 1)

Phases and Classifications of Matter

This section of the lecture will introduce some terminologies. Those terminologies matter as we continue with the course, so it would be best to start memorizing the definitions.

What is matter?

Matter is defined as anything that occupies space and has mass.

Mass is a measure of the amount of matter in it.

Note that, despite some connections, mass and mole are not exactly the same. They are different types of measurements of the amount of matter. Mass focuses more on a macroscopic perspective – 1kg of water and 1kg of gold have the same mass, thus having the same weight on Earth. However, 1kg of water and 1kg of gold have different number of particles inside them. Moles are particularly useful when we are counting how many particles are “gained” or “lost” in a chemical reaction because the definition of the mole is directly tied to the number of particles. And, not surprisingly, we can convert between mass and moles (later in this lecture).

States of Matter

There are 3 common classical states of matter (a synonym but technically distinct concept for “state of matter” is “phase”).

Solid – matter that is rigid and possesses a definite shape.
Liquid – matter that flows and takes the shape of the container.
Gas – matter that flows, takes the shape of the container, and fills the volume of the container.

Macroscopic visualization of solid, liquid, and gas. Access for free at openstax.org

There is a 4th less-common classical state of matter called the “plasma” – a gaseous state of matter that contains appreciable numbers of electrically charged particles. We will not discuss this state of matter as in-depth compared to the other 3 in this course. Similarly, we will not touch on non-classical states of matter – that’s in physics territory.

There are 2 ways to change the state of a matter.

We should be very familiar with this one – temperature. Putting water into the freezer makes ice (liquid to solid), while heating chocolate in a pot melts it (solid to liquid).
Pressure can change the state of a matter as well. If there is more pressure, the more closely packed the particles will be. So, a gas can become a solid if we only increase pressure and keep the temperature constant.

We can draw a diagram detailing the state of a matter (or phases of a matter, more specifically) based on the temperature and pressure. We call the diagram the phase diagram. Below is a phase diagram of water (heavily simplified) with temperature and pressure as the variables.

Simplified phase diagram for water. Observe the states of matter under different temperatures and pressures.

Phase Transitions

We will focus on the transitions among the common classical states of matter – solid, liquid, and gas.

Solid to liquid – Melting (chocolate in a heating pan)
Liquid to Solid – Freezing (water in the freezer)
Liquid to Gas – Vaporization (water in the boiler)
Gas to Liquid – Condensation (water vapor at room temperature)
Solid to Gas – Sublimation (dry ice at room temperature)
Gas to Solid – Deposition (water vapor at very cold temperatures)

Visualization of the processes of phase transitions.

Here is an important principle when it comes to phase transitions. We will discuss it in detail when we talk about thermochemistry in the next unit, so let’s prepare ourselves first.

During melting, vaporization, and sublimation, matter absorbs heat from the surroundings.

During freezing, condensation, and deposition, matter emits heat to the surroundings.

Here are some examples.

When we’re boiling water, the water will stay at 100 degrees Celsius because the water is undergoing vaporization.
When we put dry ice (solid carbon dioxide $CO_2$ ) on the stage for effects, the dry ice undergoes sublimation, absorbs heat from the surroundings, lowers the surrounding temperature, and allows nearby water vapor to condensate, creating a steamy/foggy stage effect.
Exposing ourselves to $100^{\circ}C$ of water vapor is more dangerous than exposing yourself to $100^{\circ}C$ water because when water vapor touches our skin, it condensates first to become $100^{\circ}C$ water, releasing heat into the surroundings, thus giving us more damage.

Classifying Matter

We talked about states of matter. Let’s talk about classifying them. We divide them like this:

Pure substances – substances that have a constant composition. For example, gold will always be $Au$ , and sucrose will always consist of 42.1% carbon, 6.5% hydrogen, and 51.4% oxygen by mass. The physical properties (explained later) like melting point, color, odor, etc. will be the same for a pure substance regardless of where it is sourced from.
Mixtures – substances that can be separated by physical changes such as evaporation. For example, egg fried rice is a mixture because we can physically separate the eggs from the rice.

We can subdivide those categories even further.

Pure substances can be subdivided into elements and compounds.
- Elements cannot be broken down into simpler substances by chemical changes. For example, iron $Fe$ , silver $Ag$ , gold $Au$ , aluminum $Al$ , sulfur $S$ , oxygen $O$ , etc. are elements. On the other hand, oxygen gas $O_2$ is not an element because it can be chemically broken down into 2 oxygen atoms.
- Compounds can be broken down into elements or other compounds through chemical changes. For example, water $H_2O$ can be broken down into elements hydrogen $H$ and oxygen $O$ . Sucrose, when heated in the absence of air, breaks down into the element carbon $C$ and the compound water $H_2O$ .

A gold nugget, made up of the element gold.

A sucrose crystal, made up of the compound sucrose.

Mixtures can be subdivided into heterogeneous and homogeneous mixtures.
- Heterogeneous mixtures are mixtures that varies from point to point. For example, Italian dressing is a heterogeneous mixture because sometimes we get a spoonful of mostly vinegar while other times we get a spoonful of oil and herbs from the same bottle of dressing.
- Homogeneous mixtures, also called solutions, have uniform composition and looks visually consistent throughout. For example, salt water is a solution because if we make sure the salt is fully dissolved, it tastes uniformly salty no matter which part of the solution. We will use the term “solution” to describe homogeneous mixtures because it’s simply less effort.

Italian dressing, a heterogeneous mixture.

Maple syrup, a homogeneous mixture, a.k.a, a solution.

It can essentially be summarized in this diagram below.

A summary of the classification of matter. Homogeneous mixture is also called “solution”. Access for free at openstax.org

Physical and Chemical Properties

Now that we know what type a particular matter is, we need to describe it. The “characteristics” of a matter is called its properties. There are 2 types of properties – physical and chemical properties.

A physical property is a characteristic of a substance that can be observed or measured without changing the identity of the substance. For example, the physical properties of water include: transparent, tasteless, odorless, liquid, high surface tension, has a boiling point of $100^{\circ}C$ and a melting point of $0^{\circ}C$ , etc.
A chemical property is a characteristic of a substance that can only be observed or measured by changing the identity of the substance. For example, the chemical properties of water include: can be an acid or a base, has a pH of 7 (unit 3 content), can participate in hydrolysis reactions, etc.

Below is a diagram describing examples of physical and chemical properties.

There are a lot of physical and chemical properties, but in reality, when describing a matter, we only list down the most important, recognizable, and relevant properties of said matter. We usually won’t mention carbon dioxide’s electric conductivity at room temperature but will mention how it can help extinguish flames. We usually won’t mention how sodium metal is odorless but will mention how it has a silver glaze, malleable, and can violently react with water.

Break Time: 10 Minutes

Take a short break! This lecture is on the longer side.

In the meantime, enjoy this composition by Wilhelm Stenhammar – a post-romantic Swedish composer, conductor, and pianist. This piece is Movement IV of his Piano Concerto No. 1 in B-Flat Major.

Lecture Content (Part 2)

Particles – Atoms, Molecules, and Ions

Suppose we have a block of element gold and an infinitely precise knife. We can cut the gold in half. However, there is a point where no matter how we angle our knives, that piece of gold cannot be cut in half. That extremely small piece of gold that cannot be cut in half is called an atom.

An atom is the smallest particle of an element that has the properties of that element and can enter into a
chemical combination.

Similarly, if we have a block of compound solid water and an infinitely precise knife, we can cut that block of ice in half till we end up with an extremely small yet uncuttable piece of ice. That piece of ice is called a molecule. However, by definition, a compound can be broken down into smaller atoms or other compounds through chemical reactions. As a result, we can conclude that molecules are made up of atoms.

A molecule consists of two or more atoms joined by strong forces called chemical bonds. (We will discuss chemical bonds in detail in this unit)

For example, the 1 mole of water is made up of $6.02\times 10^{23}$ water molecules $H_2O$ . Each water molecule is made up of 2 hydrogen $H$ atoms and 1 oxygen $O$ atom through powerful chemical bonds.

The Periodic Table

Introducing the periodic table – a chemist’s best friend and our most useful tool. Essentially, the periodic table contains almost everything we need to know, whether it is explicitly stated on the table or implied.

We can group the periodic table horizontally and vertically.

Horizontally, there are 7 rows. Each row is called a “period”. For example, phosphorous is in Period 3.
Vertically, there are 18 columns. Each column is called a “group”. For example, phosphorous is in Group 15. See the diagram (left) below.
- Some groups have names:
- Group 1 is also called alkali metals.
- Group 2 is also called alkaline earth metals.
- Groups 3-12 is also called transition metals.
- Group 15 is also called pnictogens (not a common term).
- Group 16 is also called chalcogens (not a common term).
- Group 17 is also called halogens.
- Group 18 is also called noble gases.

The periodic table in groups. Access for free at openstax.org

The periodic table color-coded in terms of metals, nonmetals and metalloids. Access for free at openstax.org

We can also group the periodic table into metals, non-metals, and metalloids. See diagram (right) above.

Metalloids are elements that conduct heat and electricity moderately well, and possess some properties of metals and some properties of nonmetals. They include:
- $B, Si, Ge, As, Sb, Te, At$ (shaded purple).
Metals are shiny, malleable, good conductors of heat and electricity. They include:
- Every element to the left of the metalloids (except hydrogen, shaded yellow).
Non-metals are elements that appear dull, poor conductors of heat and electricity. They include:
- Every element to the right of the metalloids (shaded green).

A lot of information is present in the periodic table. We will go through each information one by one. Let’s start with the chemical symbol and the name for one element.

Highlighted in yellow is the parts of the periodic table we will talk about in this section – the chemical symbol and element name.

To figure out if a matter is an element or a compound, we simply need to look at the matter’s molecular formula, which, simply speaking, is a combination of symbols from the periodic table that describes what the matter is made up of.

A molecular formula is a representation of a molecule that uses chemical symbols to indicate the types of atoms followed by subscripts to show the number of atoms of each type in the molecule. For example:

1 $CaCO_3$ molecule is made up of 1 calcium $Ca$ atom, 1 carbon $C$ atom, and 3 oxygen $O$ atoms.

2.5 moles of methane gas $CH_4$ contains 2.5 moles of carbon $C$ atoms and 10 moles of hydrogen $H$ atoms.

If we see that the molecular formula contains at least 2 different chemical symbols, we know that the matter is a compound. If there is only 1 chemical symbol in the matter’s chemical formula, we know that the matter is an element. For example:

$CH_3COOH$ is a compound, and $C$ is an element.
$AlCl_3$ is a compound, and $Al$ is an element.

The Structure of Atoms

Even though atom is the smallest unit that can enter a chemical reaction, there are even smaller particles within an atom. Those subatomic particles dictate the properties of an atom. An atom consists of electrons, protons, and neutrons. Protons and neutrons together form the nucleus, while electrons move around the nucleus at specific orbitals. Here, we introduce a new unit – the atomic mass unit (amu).

1 amu is defined as exactly 1/12 of the mass of 1 C-12 atom.

$1\ amu = 1.6605\times 10^{-24}\ g$

A proton and a neutron each have approximately 1 amu of mass, while an electron has close-to-0 mass.

Protons and electrons also have charges on them. Protons have a 1+ unit charge per proton while electrons have a 1- unit charge per electron. (The convention for charges in chemistry is to write the sign to the right)

Below is a heavily simplified diagram of a $C$ atom, alongside some subatomic particle properties.

A diagram of a simplified structure of a C-12 atom – the electrons surround the nucleus, which is composed of protons and neutrons.

Name

Unit Charge

Atomic Mass (amu)

Proton

$1.00727\approx 1$

Neutron

$1.00866\approx 1$

Electron

$0.00055\approx 0$

The video below (made by Kurzgesagt) intuitively explains what an atom is.

Protons, Neutrons, and Electrons

Let’s see how changing the number of protons, neutrons, and electrons can affect the atom.

In an atom, the number of protons determines the identity of the element. In other words, the number of protons determines the atom’s chemical properties and physical properties. For example:

If an atom has 6 protons, it will always be a carbon atom, regardless of how many neutrons or electrons there are.
If an atom has 26 protons, it will always be an iron atom, regardless of how many neutrons or electrons there are.
If an atom has 35 protons, it will always be a bromine atom, regardless of how many neutrons or electrons there are.

Pure carbon – 6 protons. It is a black solid.

Iron – 26 protons. It is a shiny silver metal.

Bromine – 35 protons. It is a dark brown liquid.

In an atom, given that the number of protons is the same, the number of neutrons determines the isotope of the atom.

Isotopes are members of a family of an element that all have the same number of protons but different numbers of neutrons.

Isotopes of the same element have different atomic masses and physical properties. Sometimes, isotopes of the same element have different nuclear stability. For example:

The element hydrogen has 3 naturally occurring isotopes: protium (>99.9% occurring), deuterium (<0.1%), and tritium (trace). They all have only 1 proton, but they have different number of neutrons.
- Protium is what we usually refer to as hydrogen (and we will keep it that way unless otherwise specified). It has 1 proton and 0 neutron. It has 1 amu and does not decay.
- Deuterium, sometimes called “heavy hydrogen”, has 1 proton and 1 neutron. It has 2 amu and does not decay.
- Tritium, even heavier than deuterium, has 1 proton and 2 neutrons. It has 3 amu and decays radioactively over time.
The element carbon has 3 naturally occurring isotopes: C-12 (>98% occurring), C-13 (<2%), and C-14 (trace). They all have 6 protons, but they have different number of neutrons.
- C-12 is what we usually refer to as carbon (and we will keep it that way unless otherwise specified). It has 6 protons and 6 neutrons. It has 12 amu and does not decay.
- C-13 has 6 protons and 7 neutrons. It has 13 amu and does not decay.
- C-14 has 6 protons and 8 neutrons. It has 14 amu and decays radioactively over time.

Isotopes of hydrogen with number of protons, neutrons, and electrons shown.

In an atom, given the same number of protons, the number of electrons determine the net charge of the atom. Usually, the atom contains an equal number of protons and electrons. Since protons and electrons have opposite but equal magnitude of charge, the charges cancel out. However, if the number of electrons is different from that of protons, the atom will have a net charge. If the atom has net charge, it is called an ion.

If # of electrons $>$ # of protons, the ion has negative charge, called an anion.
If # of electrons $<$ # of protons, the ion has positive charge, called a cation.

How we calculate the amount of net charge is:

# of protons – # of electrons.

We write the charge at the upper-right side of the chemical symbol. For example:

A chlorine atom has 17 protons.
- If it has 17 electrons, it has a net charge of $0$ , thus notated as $Cl$ .
- If it has 18 electrons, it has a net charge of $1$ – ( $17-18=-1$ ), thus notated as $Cl^-$ .
An iron atom has 26 protons.
- If it has 26 electrons, it has a net charge of $0$ , thus notated as $Fe$ .
- If it has 24 electrons, it has a net charge of $2$ + ( $26-24=2$ ), thus notated as $Fe^{2+}$ .
- If it has 23 electrons, it has a net charge of $3$ + ( $26-23=3$ ), thus notated as $Fe^{3+}$ .

The Atomic Number Notation

There is a notation that describes how many protons, neutrons, and electrons are in an atom, called the atomic number notation.

The number of protons is also called the atomic number $Z$ . The number of protons + neutrons is called the (atomic) mass number $A$ . (Yes, the symbols are weird)

The atomic number is also expressed on the periodic table.

Highlighted in yellow is the atomic number, which we will discuss in this section.

The atomic number notation is written as follows:

$^{A}_{Z}X^{charge}$

where:

X denotes the element.

Z denotes the atomic number. (usually omitted because we can just refer to the periodic table)

A denotes the mass number.

charge denotes the charge of the atom.

If we want to know the number of neutrons, simply take $A-Z$ .

For example:

C-14, the radioactive isotope of carbon, can be written as $^{14}C$ .
If C-14 somehow lost an electron, we can write that as $^{14}C^{+}$ .
Atomic number notation is most used in nuclear chemistry. In other cases, such as almost this entire course, we will simply write the chemical symbol without the mass number. We simply assume the most common isotope of the element unless otherwise specified.

Other Information on the Periodic Table

Here, we will briefly go through the other properties presented on the periodic table elements. We went through the chemical symbol, the name, and the atomic number of an element. We also went through the periods and groups of the periodic table. However, there are still some information we haven’t gone through yet.

We will discuss those properties in detail in future lectures.

Average Atomic Mass and Molar Mass

The information on the upper left displays the average atomic mass of the element. This is a measurement, so it will follow sig fig rules.

Highlighted in yellow is the average atomic mass of the element. It is numerically equivalent to the molar mass of the element.

Since we know the atomic weight of protons, neutrons, and electrons, we can estimate the atomic mass of iron to be just above 56 amu (26 protons, 30 neutrons, and 26 electrons). The reason why the measured atomic mass is slightly lower is because of a concept called mass defect – a nuclear chemistry concept that we will go through in Unit 4.

Another very closely related concept to the atomic mass is the molar mass. Interestingly, the element’s atomic mass and molar mass are numerically equivalent (different units though). We will discuss this numerical equivalence and those concepts more in the next lecture.

1st Ionization Energy

The 1st ionization energy, simply defined, is the energy required to knock 1 electron out of the atom in its gaseous phase. The reason we would want this information is that it helps determine how potentially reactive an atom/molecule is. It’s not the entire picture but it is an important part of a big picture of element reactivity. If we think about it, a charged particle is most likely a more reactive particle. So, if a particle is easier to be ionized, the particle is easier to participate in a reaction.

We will discuss ionization energy in Chapter 2.

Electronegativity

Electronegativity $\chi$ measures the tendency of an atom to attract electrons toward itself. It is kind of the opposite of the 1st ionization energy. If $\chi$ has a huge value, it means the atom attracts electrons very well. Likewise, if $\chi$ has a small value, it means the atom does not attract electrons very well.

When looking at molecules, we can look at their atoms’ electronegativity differences to determine the type of chemical bonds they have. It also can help us determine how partial charges distribute. We will talk about this in Chapter 2.

Oxidation States

We will talk more oxidation and reduction reactions in Unit 2. For now, we will discuss an important concept called oxidation states. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. Different atoms have different oxidation states in different compounds. The concept of oxidation states is practically useful when it comes to balancing equations (next lecture), understanding chemical nomenclature (next discussion), and some charge predictions. However, it is important to note that the oxidation state of an atom does not represent the “real” charge on that atom, or any other actual atomic property – it’s a formalism that has practical usage.

Here are some general rules when it comes to assigning oxidation states.

Alkali metals have an oxidation state of +1.
Alkaline earth metals have an oxidation state of +2.
Fluorine always have an oxidation state of -1.
Oxygen usually has an oxidation state of -2 (except when $F$ is involved).
Hydrogen usually has an oxidation state of +1 (except when metals are involved).
Elements in its pure form (e.g., $O_2, O_3, S_8, H_2, N_2, Br_2$ ) will always have an oxidation state of 0.
The rest can mostly be derived from these rules.

Electron Configuration

Our electron orbital in our atom diagram is heavily simplified. There are actually different orbitals electrons reside in that follow specific rules. Orbits include the s-orbital, p-orbital, d-orbital, and the f-orbital. The configuration of those electrons helps us explain how chemical bonds work.

We will talk about electron configurations in Chapter 2. The electron configuration of an atom has far-reaching implications in our chemistry journey, and we will discuss those implications in organic chemistry.

Assignments

1. Preview Questions

What are phases of matter and how are they different from each other?
What are physical and chemical properties and how are they different from each other?
What are the particles in an atom? How are they important?
What are some properties listed on the periodic table and how are they important?

2. Lecture Worksheet (TBD)

The lecture worksheet is available as a pdf file below. Remember, practice makes perfect!

3. Further Reading

The periodic table: https://en.wikipedia.org/wiki/Periodic_table

Video: “Are there Undiscovered Elements Beyond The Periodic Table?” by PBS Space Time
Video: “A Boy And His Atom: The World’s Smallest Movie” by IBM

You finished the lecture! It’s a long lecture, so let’s take a break for today – it takes time for our brain to fully absorb new materials. Don’t forget to review!

Project MEEP

General Chemistry

Image Attributions and Citations

Some images (with dots as background) are original creations using canva.com

Solid, liquid, and gas particle demonstrations:
By Julio Miguel A Enriquez and Monica Muñoz – Wiki Learing Tec de Monterrey, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=64130757
By Julio Miguel A Enriquez and Monica Muñoz – Wiki Learing Tec de Monterrey, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=64130758
By Julio Miguel A Enriquez and Monica Muñoz – Wiki Learing Tec de Monterrey, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=64130770
Phase diagram: By author of the original work: Cmglee – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=34865054
Gold nugget: See page for author, Public domain, via Wikimedia Commons, https://commons.wikimedia.org/wiki/File:GoldNuggetUSGOV.jpg
Sucrose crystals: Nachovfranco, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons, https://commons.wikimedia.org/wiki/File:Sucrose_crystals.JPG

Periodic table: 2012rc, CC BY 3.0 https://creativecommons.org/licenses/by/3.0, via Wikimedia Commons, https://commons.wikimedia.org/wiki/File:Periodic_table_large.svg
Pure carbon: Texas Lane, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons, https://commons.wikimedia.org/wiki/File:Pure_Carbon.png
Iron: Alchemist-hp (talk) (www.pse-mendelejew.de) (FAL or GFDL 1.2 http://www.gnu.org/licenses/old-licenses/fdl-1.2.html), via Wikimedia Commons, https://commons.wikimedia.org/wiki/File:Iron_electrolytic_and_1cm3_cube.jpg
Bromine: Alchemist-hp (pse-mendelejew.de), CC BY-SA 3.0 DE https://creativecommons.org/licenses/by-sa/3.0/de/deed.en, via Wikimedia Commons, https://commons.wikimedia.org/wiki/File:Bromine_vial_in_acrylic_cube.jpg
Hydrogen isotopes: Dirk Hünniger; Derivative work in english – Balajijagadesh, CC BY-SA 3.0 https://creativecommons.org/licenses/by-sa/3.0, via Wikimedia Commons, https://commons.wikimedia.org/wiki/File:Hydrogen_Deuterium_Tritium_Nuclei_Schmatic-en.svg