4.3 Electron Configurations

Summary

This educational video script explains electron configurations in atoms, emphasizing the preference for the lowest energy state. It outlines the Aufbau principle, which directs electron placement starting from 1s to higher energy levels. The Pauli exclusion principle is highlighted, stating no two electrons can share all four quantum numbers identically, affecting their spin states. Hund's rule is also discussed, advocating for single electron occupancy in equal energy orbitals before pairing. The script further illustrates how to represent electron configurations using orbital notation, electron configuration notation, and noble gas notation, simplifying the depiction of atoms' electron structures.

Takeaways

• 🔬 Atoms and electrons prefer to be in the lowest energy state possible, with electrons tending to occupy lower energy orbitals first.
• 📚 The Aufbau principle dictates that electrons fill the lowest energy orbitals first, following a specific order: 1s, 2s, 2p, 3s, 3p, and so on.
• 🔄 The energy levels don't simply increase sequentially; for example, the 4s sublevel has lower energy than the 3d sublevel.
• 👥 The Pauli exclusion principle states that no two electrons in the same atom can have the same set of four quantum numbers, leading to opposite spins in the same orbital.
• 🧲 Hund's rule asserts that equal energy orbitals must each be occupied by one electron before any can be doubly occupied, minimizing electron repulsion and lowering energy.
• 📊 Orbital notation is a way to represent electron configurations by drawing lines for orbitals and arrows for electrons, indicating their spin states.
• 📝 Electron configuration notation simplifies the representation by using the orbital name with a superscript to show the number of electrons, e.g., 1s² for helium.
• 🌐 The highest energy level with electrons is known as the highest occupied energy level, and its electrons are the valence electrons, which are reactive in chemical reactions.
• 💠 Inner shell electrons are those in lower energy levels and are generally unreactive, being 'hidden' by the outer energy levels.
• 🏺 Noble gas notation is a shorthand for electron configurations, using the configuration of the preceding noble gas and adding the outermost electrons, making it easier to write configurations for elements beyond the first few periods.

Q & A

What is the primary preference of electrons in atoms?

Electrons in atoms prefer to be in the lowest energy state possible, which means they tend to occupy the ground state and fill lower energy orbitals first.

What is the Aufbau principle and how does it relate to electron configuration?

The Aufbau principle states that electrons fill the lowest energy orbitals first, following a specific order: 1s, 2s, 2p, 3s, 3p, and so on, as indicated by increasing energy levels.

Why do electrons fill the 4s orbital before the 3d orbital even though 3d is higher in the periodic table?

According to the Aufbau principle, the 4s orbital is lower in energy than the 3d orbital, so electrons fill the 4s orbital before the 3d orbital, despite the order in the periodic table.

What does the Pauli exclusion principle state about electrons in an atom?

The Pauli exclusion principle states that no two electrons in the same atom can have the same set of four quantum numbers, which means that electrons in the same orbital must have opposite spins.

What is Hund's rule and how does it affect the filling of orbitals?

Hund's rule states that equal energy orbitals must each be occupied by one electron with the same spin before any orbital is doubly occupied, which minimizes electron repulsion and lowers the overall energy of the atom.

How is orbital notation used to represent electron configurations?

Orbital notation represents electron configurations by drawing lines for orbitals and arrows for electrons, with the arrows indicating the spin state of each electron and the name of the orbital below it.

What is electron configuration notation and how is it different from orbital notation?

Electron configuration notation is a simpler way to represent electron configurations by writing the name of the orbital with a superscript to indicate the number of electrons in that orbital, as opposed to drawing out each electron and orbital.

What are valence electrons and why are they important in chemistry?

Valence electrons are the electrons in the highest energy level of an atom, which are involved in chemical reactions. They are important because they determine the reactivity of an element.

What is the significance of the term 'octet' in the context of electron configurations?

The term 'octet' refers to a complete outer energy level with eight electrons, which is a stable configuration that makes elements unreactive, like those found in the noble gases group of the periodic table.

How does noble gas notation simplify writing electron configurations for elements?

Noble gas notation simplifies electron configurations by using the electron configuration of the preceding noble gas in brackets, followed by the additional electrons that are unique to the element, thus avoiding the need to write out the entire configuration.

Why are the 1s electrons in an atom considered inner shell electrons?

The 1s electrons are considered inner shell electrons because they are in a lower energy level and are less involved in chemical reactions, being 'hidden' behind the higher energy levels where valence electrons are located.

Outlines

00:00

🔬 Electron Configurations and Energy States

This paragraph introduces the concept of electron configurations, emphasizing that electrons, like the rest of the universe, prefer to be in the lowest energy state possible. It explains that electrons fill orbitals in a specific order, starting with the lowest energy orbitals (1s, 2s, 2p, etc.) and following the Aufbau principle, which dictates that electrons occupy the lowest energy orbitals first. The paragraph also discusses the energy levels of suborbitals, noting that the 3d suborbital is higher in energy than the 4s suborbital. It introduces the Pauli Exclusion Principle, stating that no two electrons in the same atom can have the same set of four quantum numbers, leading to electrons in the same orbital having opposite spins. Lastly, it mentions Hund's Rule, which states that electrons will occupy equal-energy orbitals singly before pairing up to minimize repulsion and maintain lower energy states.

05:01

📚 Representing Electron Configurations

The second paragraph delves into the different ways to represent electron configurations. It starts with orbital notation, which involves drawing lines for orbitals and arrows for electrons, indicating their spin states. The paragraph then moves on to electron configuration notation, a simpler method that uses the orbital name with a superscript to show the number of electrons it contains. Examples are given for hydrogen, helium, and lithium, illustrating how the notation reflects the electron filling process. The concept of valence and inner shell electrons is introduced, with valence electrons being in the outermost energy level and thus more reactive. The paragraph also explains the highest occupied energy level and how it relates to chemical reactivity. A visual representation using color-coded energy levels and suborbitals is briefly mentioned, providing a simplified model for understanding electron configurations.

10:03

✍️ Noble Gas Notation for Electron Configurations

The final paragraph discusses the use of noble gas notation as a shorthand for writing electron configurations, particularly useful for elements beyond helium. It explains that the electron configuration of a noble gas can be used as a base, with additional electrons noted separately. This method simplifies the process of writing electron configurations, as it eliminates the need to write out the full configuration of inner shell electrons. The paragraph uses sodium as an example, showing how its electron configuration can be abbreviated using neon's configuration followed by the additional 3s1 electron. This notation is especially helpful for elements with more complex electron configurations, making it easier to represent and understand their electronic structures.

Keywords

💡Electron Configurations

Electron configurations refer to the distribution of electrons in an atom's orbitals. The video script emphasizes that electrons prefer to occupy the lowest energy states possible, which is the basis for understanding how electrons are arranged in atoms. This concept is central to the video's theme as it sets the stage for discussing the rules governing electron distribution.

💡Ground State

The ground state is the lowest energy state of an atom or molecule. In the script, it is mentioned that electrons tend to be in the ground state, which is as close to the nucleus as possible. This is a fundamental concept in the video as it explains why electrons fill orbitals in a specific order, starting with the lowest energy levels like 1s, then 2s, 2p, and so on.

💡Aufbau Principle

The Aufbau principle is a rule that describes the order in which electrons fill atomic orbitals. As explained in the script, electrons fill the lowest energy orbitals first, following the order of increasing energy levels. This principle is crucial for understanding the electron configurations of elements and is illustrated in the video through the step-by-step filling of orbitals.

💡Pauli Exclusion Principle

The Pauli Exclusion Principle states that no two electrons in an atom can have the same set of four quantum numbers. This principle is highlighted in the script to explain why electrons in the same orbital must have opposite spins. It is essential for understanding the arrangement of electrons within orbitals and the formation of electron pairs.

💡Hund's Rule

Hund's Rule asserts that equal energy orbitals must each be occupied by one electron before they can be filled by two electrons with the same spin. The script uses this rule to explain why electrons fill orbitals in a way that minimizes electron repulsion and results in lower energy states. This rule is particularly relevant when discussing the filling of p orbitals, which have three suborbitals.

💡Orbital Notation

Orbital notation is a method of representing electron configurations by drawing lines for orbitals and arrows for electrons, indicating their spin states. The script introduces this notation as a way to visualize electron configurations, with examples provided for hydrogen, helium, and lithium. This notation helps in understanding the distribution of electrons across different energy levels and suborbitals.

💡Electron Configuration Notation

Electron configuration notation is a shorthand way of writing the electron configuration of an atom, using the names of orbitals and superscripts to denote the number of electrons. The script demonstrates this notation with examples for hydrogen, helium, and lithium, showing how it simplifies the representation of electron distributions. This notation is key to understanding the electron configurations of elements in the periodic table.

💡Valence Electrons

Valence electrons are the electrons in the outermost energy level of an atom, which are involved in chemical reactions. The script explains that these electrons are in the highest occupied energy level and are crucial for chemical bonding. The concept is integral to the video's theme as it connects electron configurations to chemical reactivity and the properties of elements.

💡Inner Shell Electrons

Inner shell electrons are those that are not in the outermost energy level and are generally less involved in chemical reactions. The script contrasts these with valence electrons, indicating that inner shell electrons are 'hidden' behind the outer shell and are more unreactive. This distinction is important for understanding the chemical inertness of noble gases and the stability of full outer shells.

💡Noble Gas Notation

Noble gas notation is a shorthand method for writing electron configurations by using the configuration of the noble gas that precedes the element in the periodic table, followed by the additional electrons. The script introduces this notation as a time-saving technique, especially for elements with many electrons. This notation is demonstrated for sodium, showing how it simplifies the representation of electron configurations while still capturing the essential information.

💡Octet Rule

The octet rule states that atoms tend to form compounds so that they have eight electrons in their valence shell, which is a stable configuration. The script mentions this rule in the context of neon, which has a full outer energy level with eight electrons, making it unreactive and a noble gas. The octet rule is a fundamental concept in chemistry for predicting the valency and reactivity of elements.

Highlights

Atoms and electrons prefer to be in the lowest energy state possible.

Electrons occupy lower energy levels first, such as 1s before 2s, 2p, etc.

The Aufbau principle dictates that electrons fill the lowest energy orbitals first.

Electron configuration follows a pattern: 1s, 2s, 2p, 3s, 3p, with exceptions for higher energy levels.

The Pauli exclusion principle states no two electrons in an atom can have the same set of four quantum numbers.

Electrons in the same orbital must have opposite spins due to the Pauli exclusion principle.

Hund's rule states that equal energy orbitals must each be occupied by one electron before any can be doubly occupied.

Electron configurations can be represented in orbital notation with arrows indicating spin.

Electron configuration notation simplifies representation by using superscripts to indicate electron count.

The highest occupied energy level contains valence electrons, which are involved in chemical reactions.

Inner shell electrons are unreactive and are 'hidden' by the outer energy level's electrons.

The octet rule states that a complete outer energy level with eight electrons results in an unreactive atom.

Noble gases have full outer energy levels, making them unreactive and placing them on the far right of the periodic table.

Noble gas notation is a shorthand for electron configuration, using the noble gas's configuration plus additional electrons.

Electrons fill orbitals following the Aufbau principle, starting with the lowest energy and moving upwards.

The electron configuration for neon, a noble gas, is 1s2 2s2 2p6, representing a full outer shell.

For elements following neon in the periodic table, noble gas notation is used for electron configuration.

Transcripts

so today we're gonna be covering chapter

4 section 3 which is electron

configurations and the first thing you

need to know is that atoms and electrons

like most the rest of the universe like

to be in the lowest energy state

possible now what does that mean it

means that for electrons they like to be

in the ground state as close as possible

so as you can see this arrow indicates

increasing energy going down this way so

electrons tend to be in the lower

elements at least they occupy 1s first

than 2s 2p etc following these arrows

which indicate higher and higher energy

so there are some rules that govern how

electrons are configured in atoms and

the first is something called the Alpha

principle and what the Aufbau principle

basically says is that electrons will

first occupy the lowest energy possible

so they follow this rule right here and

you can see that again on the diagram

where they start here at the low energy

and then gradually increase following

these red arrows another thing you'll

notice is it tends to follow and a

pattern regards the number of the

orbital so it starts with 1 s and then

2s 2p 3s 3p etc but once you get up

above 1 & 2 it follows a strange thing

where the D or suborbital is actually

higher energy than the S sub orbital of

the next energy level so what ends up

happening is that electrons will fill up

for example the 4s orbital before they

fill up the e3d the next rule is

something called the Pauli exclusion

principle which is something you find in

both chemistry and physics and what the

poly exclusion principle says is that no

two electrons in the same atom can

have the same four quantum numbers and

basically what that means is that two

electrons that are in the same orbital

for example this one s orbital have to

have opposite spins because their other

three quantum numbers are the same so

let's say one has a spin of 1/2 that

means the other electron in that orbital

has to have a spin of negative 1/2 and

the last rule which we're covering today

which is hund's rule says that equal

energy orbitals must each be occupied by

one electron before they can be filled

by two and what this does is that minify

minimizes electron repulsion and ensures

that they have a lower energy because

there's not as much repulsion and so

basically what this means is if we

represent the spin numbers of negative

1/2 and 1/2 for electrons with arrows if

you're filling up an orbital let's say

this is a p orbital so that has three

subl rules of each let's say it's the 2p

over here it means that you have to fill

up each sub orbital with one electron so

if you were to go keep going you could

fill these three if you were to add

another electron you'd have to fill

these three before you could go back in

and then fill in this one with two

electrons and opposite spin States

because having these two electrons in

the same sub orbital while it is allowed

it's required that you do this state

first which has a lower energy because

these electrons will tend to repel each

other so how do we simplify this system

and represent these electron

configurations in like a better manner

well there's a few ways the first is

called orbital notation which is

probably the simplest way because it

involves drawing out every single

electron and in this case orbitals are

represented by lines like this and

electrons are represented simply by

arrows indicating their spin state

with the name of the orbital below it so

let's say this is the 1s orbital and if

we just put one electron in there that

would be hydrogen and then if you put a

second one in there

notice how I'm flipping the arrow around

to obey the Pauli exclusion principle

then this would become helium and then

we would do is go on to the next orbital

in the width in which case the next

lowest energy orbital is 2s and you'd

throw another electron in there and then

it would become lithium the second way

is something known as a simply electron

configuration notation and this is a lot

simpler because it just involves writing

and is more representative and basically

what you do is you use the name of the

orbital but with a superscript to

indicate the number of electrons in that

orbital let me demonstrate

so for example for hydrogen you would

write the orbital 1s 1 or 1 s rather and

then indicate the number of electrons in

this case just one helium you would do

I'm sorry 1 s and then 2 electrons and

for lithium the third element you would

fill up that orbital 1s 2 to obey the

outfile principle and then you would

move on to the next lowest orbital 2s

and then the number of electrons is just

1 again and just for some quick

terminology this 2s which is the highest

energy level in lithium which has an

electron in it is called the highest

occupied energy level and what that

means for the other electrons this is

also the electrons that are in this

energy level the two are also known as

valence electrons because they are the

ones that end up reacting during

chemical reactions and what that means

is these

1s2 electrons become what are known as

inner shell electrons which basically

means their unreactive they're sort of

hidden behind the energy level the shell

of the second orbital alright so here we

have what is somewhat close to a Bohr

model of the atom it's not quite

accurate but each orbital is represented

or sorry each energy level is

represented by color associations so or

energy level one is blue and energy

level two is red and then the sub

orbitals are represented by rings again

this is inaccurate the P orbitals are

actually sort of dumbbell shaped things

oriented around the new creel nucleus

differently but what this gives us is a

chance to see how you fill the orbitals

or at least the notation corresponding

to adding electrons so let's say you had

an atom of hydrogen so you just had one

electron here you just add the arrow

there or helium you'd again follow this

to obey the Pauli exclusion principle

and then if you moved on up to lithium

yet you're out of room in this lower

lowest energy level of 1s so you have to

move on up to obey the Aufbau principle

and then again you fill it up here and

again flipping the arrows to make sure

the spin states are opposite so that the

electrons can coexist and then here's

where it gets trickier if you want to

move on to boron let's say which is 1s2

2s2 2p1 you had the electron and then

let's skip a few let's go there's carbon

there's nitrogen there's oxygen alright

so then you had the arrow here here and

then you can come back and start filling

in like this

and you can continue with fluorine and

neon by filling in the rest of the

arrows and these all here in the second

energy level are valence electrons

because these are in the reactive outer

shell whereas these 1s1 are what are

called inner shell electrons and if you

wanted to write this all in electron

configuration notation you would put the

1s with two electrons 2's two electrons

and 2p with six electrons and that

corresponds to neon on the periodic

table now because neon has this full

outer shell or frontal outer energy

level rather it's the same thing with

different terminology of eight electrons

it follows something as which is called

the octet which basically means that

once it's filled completely this outer

energy level with eight electrons

it is now unreactive which is why it's

in a group called the noble gases which

you can see on the far right of your

periodic table and while this seems like

a lot of writing every time luckily

there is a shorthand known as noble gas

notation so for example if you wanted to

write the electron configuration

notation for sodium which has an

electron out here as well as the 1s2 2s2

2p6 you'd have to write out 1s2 2s2 2p6

3s1 and that would take forever if you

were to write it out for every element

so what you'll notice is that this part

is the exact same as neon so what you

can do is take the noble gas element

that precedes any element in the

periodic table obviously you can't do

this for hydrogen because it doesn't

have a noble gas that precedes it only

helium is the first one and that comes

after hydrogen but what you can do is

for every other element you can put that

in brackets as a substitute for all this

writing over here and then just add on

the additional part so the noble gas

notation for

sodium would be neon in parentheses with

the 3s1 on the end