7 min read•Last Updated on June 18, 2024
Dalia Savy
Jeremy Kiggundu
Dalia Savy
Jeremy Kiggundu
We're back to atoms! Remember how small they are? ⚛️
Recall that an atom is made up of three subatomic particles:
Subatomic Particle | Location | Mass (amu) | Charge | Extra Information |
Protons | Nucleus | ~1 | +1 | Represented by the atomic number of an element and makes up part of the mass number. |
Neutrons | Nucleus | ~1 | 0 | Makes up part of the mass number of an element. |
Electrons | Orbitals | ~0 | -1 | Represented by the atomic number of an element of zero charge. |
One of the principles that chemists use to understand atoms is Dalton’s Atomic Theory, which has four parts.
Now that we know the structure of an atom, we’ll need to be able to calculate the force, or attraction, between two atoms. This is where Coulomb's Law comes in:
The formula above is made up of the following variables:
You don't have to memorize this formula, but you should understand that the strength of the forces depends on two factors:
We're back to electrons! We know that each element has a certain number of electrons, but how do we represent them? In this section, we also learn about how to properly write out the electron configuration of an element.
Let's begin with the basic Bohr Model. Neils Bohr predicted that electrons orbit the nucleus in a circular orbit just like how the planets in our solar system orbit the Sun. ☀️🪐
However, unlike the planets in our solar system, Bohr's orbits exist only at specific, fixed distances from the nucleus. This causes the energy of each orbit to be fixed, quantized, or stationary.
Let's look at the Bohr model of sodium, which has 11 electrons.
The atomic number of sodium is 11, which indicates that there are both 11 protons and electrons. This is why there are 11 electrons represented in the above diagram.
Bohr understood that electrons in an atom are arranged in a set of electron shells, or energy levels, around the nucleus. Each energy level corresponds to a specific energy state of the electron, which is again, fixed.
He also made the connection that the closer an electron is to the nucleus, the less energy the electron has. Therefore, the valence electrons, or the outermost electrons, have the most energy. Valence electrons are found on the valence shell of an atom, or the outermost energy level.
Taking a look at the above diagram, you can see that there is only one valence electron in the valence shell.
Electron configuration refers to the arrangement of electrons in an atom or molecule. The idea behind electron configuration is quite similar to drawing out the shells in the Bohr model, in that each shell only holds a certain number of electrons.
Not only are the electrons in different energy levels, or shells, but they are also located in different subshells. The four different subshells are s, p, d, and f. The maximum number of electrons in each subshell, respectively, are 2, 6, 10, and 14.
Outer electrons are called valence electrons, while inner electrons are called core electrons.
Here is a breakdown of the different subshells on the periodic table:
This will be super helpful when we begin writing the electron configurations from scratch, but first, there are some rules to cover for writing them.
Let's begin with an easy example: boron (element 5).
If you compare boron's spot on the periodic table to the labeled one above, you would see that Boron is in the "2p" spot. You must memorize the labeled periodic table in order to write out the electron configuration of atoms.
To start, you should put your finger on the element you are trying to find (boron). Then, start at Hydrogen (1s) and read the periodic table as if you are reading a book. Therefore, you would go to helium, and then down to lithium all the way to boron.
To know the electron configuration, note all of the subshells that you passed on your way to boron, which in this case, would be 1s, 2s, and 2p.
Now, how many elements did you pass in each block?
1s: H, He = 2
2s: Li, Be = 2
2p: B = 1
These numbers represent electrons and are noted as superscripts in the electron configuration. Putting it all together, Boron's electron configuration is:
To understand this conceptually, the superscripts are an electron. Boron's atomic number of 5 indicates that it has 5 electrons, and all the superscripts added up are equal to 5. The electron configuration is telling us that 2 electrons occupy the 1s orbital, 2 electrons occupy the 2s orbital, and one electron occupies the 2p orbital.
The noble gas shortcut becomes especially helpful if you are asked to write the configuration of an element really far into the periodic table, such as element 86. Let's start practicing using the noble gas shortcut with boron.
To do this, you would go to the noble gas before Boron and then start reading the periodic table from there instead of from Hydrogen. Since Helium is the noble gas before Boron, the electron configuration would read:
You could use either method to write electron configurations, just make sure you put brackets around the noble gas if you choose the shortcut.
You may also see electron configurations represented like this, in orbital diagrams:
Each arrow here represents a singular electron. The Aufbau Principle is easily seen here since the electrons are filling up orbitals in the order of increasing energies (1s ➡️ 2s ➡️ 2p).
Pauli's Exclusion Principle is represented here as well by the arrows facing opposite directions. No two electrons can face the same way, or in reality, spin the same way in a single subshell.
Hund's Rule isn't actually represented here since there is only one electron in the 2p orbital, but here is a good visual:
The left is correct since the electrons are filling unoccupied orbitals before pairing up with one another. Remember that this occurs so that the electron fills the lowest energy orbital first! Everything in chemistry strives for the lowest energy possible.
Here is Fe on the periodic table:
Fe actually includes the d block in its electron configuration, and it is listed after the 4s orbital. Here it is:
Just make sure to include the d block! You got this, just keep practicing. It is very unlikely that you will be asked to write the electron configuration of an atom in the f block.
If you wanted to use the Nobel gas shortcut for iron, you would have to use argon in brackets!
Given the following electron configuration of As, how many valence electrons does one atom of As have?
First, you always want to look at the outermost shell, which in this case, is n=4. Remember, only the electrons in the s and p orbital are valence electrons! Therefore, you just add up the electrons in the 4s orbital and the 4p orbital, giving you a total of 5 valence electrons.
Atomic Theory is a scientific theory proposing that matter is composed of small indivisible particles called atoms.
Term 1 of 24
Atomic Theory is a scientific theory proposing that matter is composed of small indivisible particles called atoms.
Term 1 of 24
Atomic Theory is a scientific theory proposing that matter is composed of small indivisible particles called atoms.
Term 1 of 24
Subatomic particles are particles smaller than an atom. They include protons, neutrons, and electrons which make up atoms.
Quarks: Fundamental particles that combine to form protons and neutrons.
Leptons: A group of subatomic particles that includes electrons.
Bosons: Particles responsible for all physical forces except gravity.
Protons are positively charged subatomic particles found within atomic nuclei.
Neutrons: Neutral subatomic particles found within atomic nuclei alongside protons.
Atomic Number: The number of protons in an atomic nucleus which determines its chemical properties and place in the periodic table.
Ion: An atom or molecule with a net electric charge due to loss or gain of one or more electrons.
Neutrons are subatomic particles found in the nucleus of an atom. They have no electric charge and a mass slightly larger than that of a proton.
Proton: A positively charged particle located within the atomic nucleus.
Atomic Mass Unit (AMU): A unit of mass used to express atomic and molecular weights, roughly equivalent to the mass of one nucleon (either a proton or neutron).
Strong Nuclear Force: The force that acts between protons and neutrons in an atomic nucleus, overcoming electromagnetic repulsion and holding them together.
Electrons are subatomic particles with a negative electric charge. They orbit around the nucleus of an atom in specific energy levels or shells.
Orbitals: Regions around the nucleus where electrons are most likely to be found.
Valence Electrons: The electrons present in the outermost shell of an atom that participate in chemical reactions.
Ionization Energy: The amount of energy required to remove an electron from its orbital.
Orbitals are regions around the nucleus of an atom where electrons are most likely to be found. They come in different shapes and energy levels.
Sublevels: These are divisions within principal energy levels that contain one or more orbitals. Like different sections within a dog park.
Quantum Numbers: These numbers describe properties of atomic orbitals and their electron occupants; they're like ID tags for dogs at each park.
Pauli Exclusion Principle: A principle stating that no two electrons can occupy the same quantum state simultaneously; it's like saying no two dogs can have the same ID tag.
Atomic Theory is a scientific theory proposing that matter is composed of small indivisible particles called atoms.
Element: A substance consisting entirely from one type of atom.
Compound: A substance formed when two or more chemical elements are chemically bonded together.
Chemical Bond: The attraction between atoms that allows the formation of chemical substances that contain two or more atoms.
Coulomb's Law describes the force between two charged objects. It states that this force is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.
Electric Charge: This is a fundamental property of matter that can be either positive or negative, with like charges repelling and opposite charges attracting each other.
Inverse Square Law: This law states that a specified physical quantity or intensity is inversely proportional to the square of the distance from the source of that physical quantity.
Force Field: A region around a charged particle within which a force would be exerted on other charged particles or objects.
Electric Force is an interaction between two charged objects. Depending on whether these objects carry similar or different types of charge, this force can result in attraction (opposite charges) or repulsion (like charges).
Electrostatics: The study of electric charges at rest and their electric fields and potentials.
Coulomb’s Constant: A proportionality constant used in equations relating electric forces between particles and their distances apart.
Field Lines: Imaginary lines representing the direction and strength of an electric field.
Coulomb's Constant, denoted by k, is a proportionality constant that appears in Coulomb's Law. It helps to calculate the electric force between two charged objects.
Permittivity of Free Space: A measure of a material’s ability to transmit (or 'permit') an electric field.
Electric Field: The region around a charged particle within which other charges experience a force.
Electrostatic Force: The attractive or repulsive interaction between any two charged objects.
Electron configuration is the arrangement of electrons in an atom, molecule, or other physical structure.
Aufbau Principle: This principle states that electrons fill up the lowest energy levels first before moving on to higher ones. It's like filling up the front rows at a concert before letting people into the back rows.
Pauli Exclusion Principle: This principle says that no two electrons can have identical quantum states. Imagine it as each person having their own unique seat at the wedding; no two people can sit in exactly the same spot!
Hund's Rule: Hund's rule states that every orbital in a subshell is singly occupied with one electron before any one orbital is doubly occupied. It’s like ensuring each room in a house has one occupant before anyone gets a roommate!
Proposed by Niels Bohr, this model describes an atom as having a central nucleus surrounded by electrons in specific energy levels or orbits.
Quantum Mechanical Model: A model that uses complex shapes of orbitals (regions around the nucleus where an electron is likely to be found), volumes of space in which there are likely to be electrons.
Energy Levels: The specific energies an electron in an atom can have.
Orbitals: Regions within an atom where electrons are most likely to be found.
Neils Bohr was a Danish physicist who made foundational contributions to understanding atomic structure and quantum theory. He proposed the Bohr model of the atom, where electrons move in fixed orbits around the nucleus.
Quantum Mechanics: The branch of physics dealing with the behavior of particles on a very small scale, such as atoms and subatomic particles. It's like the rules that govern how our city operates.
Atomic Structure: The arrangement of protons, neutrons, and electrons within an atom. This is like the layout or blueprint of our city.
Electron Configuration: The distribution of electrons in an atom or molecule's electron shells. It's like deciding which buildings go on which streets in our city.
Energy levels are the fixed amounts of energy that a system (like an atom or molecule) can have. In an atom, they're the specific distances from the nucleus where electrons may reside.
Ground State: The lowest energy state of an atom or other particle. It's like being on the first floor of our skyscraper.
Excited State: A state in which an atom has more energy than it does at its ground state. This is like taking the elevator up to a higher floor in our skyscraper.
Quantum Leap: When an electron moves from one energy level to another, often releasing or absorbing energy. It's like jumping between floors in our skyscraper without using stairs or elevators.
Valence electrons are the outermost electrons in an atom that participate in chemical reactions.
Electron Shell: This is like a layer of an onion, where each shell can hold a certain number of electrons. The outermost shell is where you'll find the valence electrons.
Covalent Bond: This is when two atoms share their valence electrons, kind of like how best friends might share their favorite toys.
Ionization Energy: This is the energy required to remove a valence electron from an atom. It's like how much effort it would take for someone to pry your favorite toy out of your hands!
Subshells are a division of electron shells separated by different quantum numbers. They are designated as s, p, d, and f.
Shell: This is the energy level of an atom where electrons reside. It's like the "room" in our mansion analogy.
Quantum Numbers: These are values that describe the characteristics of electrons such as their energy level (shell), shape (subshell), orientation in space, and spin direction.
Orbital: This is a region within an atom where there's a high probability to find an electron. It's like specific spots within our subshell "areas".
Core electrons are the inner, non-reactive electrons found within an atom.
Atomic Number: This represents the total number of protons in an atom's nucleus. It's similar to your ID number; it identifies who you are (or what element an atom is).
Noble Gases: These elements have full electron shells and don't usually react with other elements because they're content just as they are - kind of like someone who prefers staying home instead of going out partying!
Shielding Effect: This describes how core electrons shield or protect the positive charge from the nucleus from reaching the outer (valence) shell. Imagine them as bodyguards protecting a celebrity (the nucleus) from fans (the valance shell).
The Aufbau Principle states that electrons occupy the lowest energy levels first before moving on to higher energy levels.
Ground State: This refers to the lowest energy state of an atom or other particle. In our concert analogy, it would be those front row seats!
Excited State: This is when an electron absorbs enough energy to move from its normal state into a higher-energy orbital - kind of like getting bumped up from regular seating at a concert into VIP!
Electron Configuration: This describes how electrons are distributed among atomic orbitals - think about it as who sits where during our concert.
The Pauli Exclusion Principle states that no two electrons in an atom can have the same four quantum numbers, meaning each electron in an atom has a unique state.
Spin Quantum Number: This is one of the four quantum numbers. It describes the spin direction (up or down) of an electron - kind of like whether our student prefers to sit upright or slouch!
Hund's Rule: This rule states that every orbital in a subshell is singly occupied before any orbital is doubly occupied. It's like ensuring every desk in a classroom has one student before any desk gets two students.
Quantum Mechanical Model: This model describes the behavior of electrons in atoms. It's like the school handbook that outlines how students should behave and where they should be at certain times.
Orbital diagrams are pictorial descriptions of the electrons in an atom and their placement within energy levels.
Quantum Numbers: Set of four numbers used to describe an electron's energy state in an atom.
Pauli Exclusion Principle: The principle that states no two electrons in an atom can have identical quantum mechanical states.
Aufbau Principle: The rule that electrons occupy the orbitals of lowest energy first.
Hund's Rule states that electrons will occupy empty orbitals in the same sublevel before they pair up in the same orbital.
Electron Configuration: The distribution of electrons of an atom or molecule (or other physical structure) in atomic or molecular orbitals.
Orbital: A region around the nucleus of an atom where there is a high probability of finding an electron.
Sublevel: An energy level defined by quantum theory. In chemistry, sublevels refer to energies associated with electrons.
The Noble Gas Shortcut is a method used to simplify writing out electron configurations for elements by using the previous noble gas configuration as a starting point.
Noble Gases: Elements in group 18 on the periodic table. They are colorless, odorless, tasteless, nonflammable gases at room temperature.
Periodic Table: A tabular arrangement of chemical elements, organized based on their atomic number, electron configuration and recurring properties.
Electron Configuration Notation: A notation that shows exactly which orbitals contain how many electrons.