GCSE Chemistry - Electron Arrangement #8

Summary

This educational video explores electron arrangement in atoms, highlighting the importance of a full outer shell for stability. It demonstrates the electron configuration of sodium and explains how atoms like it tend to react to achieve stability. The video also covers noble gases, which are stable due to full outer shells, and provides examples of how to determine electron structures for elements like argon and calcium. It concludes with the case of fluorine, which gains an electron to become a fluoride ion, emphasizing the concept of ions and their charges.

Takeaways

• 🔬 Atoms strive for a stable electron configuration, typically seeking a full outer shell.
• 🚀 Sodium, with an atomic number of 11, has an electron arrangement that leaves its outer shell with only one electron, making it unstable.
• 📚 The first electron shell holds up to two electrons, while the second and third can hold up to eight each.
• 🌐 Electrons are added to shells in a specific order, starting with single electrons in corners before filling in pairs.
• 💡 Noble gases, like neon, have full outer shells and are chemically stable due to this configuration.
• 📖 For exam preparation, knowing the electron arrangement of the first 20 elements in the periodic table is crucial.
• 🌀 Argon, with an atomic number of 18, has a full outer shell with its electron configuration written as 2, 8, 8.
• 📝 Electron configurations can be represented numerically, showing the count of electrons in each shell.
• ⚡ Calcium, with 20 electrons, has an unstable outer shell with only two electrons out of eight possible, leading to a +2 charge as a calcium ion.
• 🔋 Ions are represented with square brackets and the overall charge indicated in the top right corner.
• 🌿 Fluorine, needing one more electron for a full outer shell, gains an electron to become a fluoride ion with a -1 charge.

Q & A

Why do atoms need a full outer shell of electrons to be stable?

Atoms need a full outer shell of electrons to be stable because a complete outer shell means they have reached a stable electron configuration, typically resembling the noble gases, which are chemically inert due to their full valence electron shells.

What is the atomic number of sodium, and how does this relate to its electron configuration?

The atomic number of sodium is 11, which means it has 11 protons and also 11 electrons. These electrons are arranged in shells around the nucleus, with the first shell holding 2 electrons and the second shell holding up to 8, leaving the third shell with 1 electron, making the outer shell incomplete.

How does the electron arrangement in an atom influence its chemical reactivity?

The electron arrangement, specifically the completeness of the outer shell, influences an atom's chemical reactivity. Atoms with incomplete outer shells tend to react with other atoms to gain, lose, or share electrons to achieve a stable electron configuration.

What is the maximum number of electrons that the first and second shells can hold?

The first shell can hold a maximum of 2 electrons, while the second shell can hold up to 8 electrons.

Why are noble gases chemically inert?

Noble gases are chemically inert because they have completely full outer electron shells, which means they are already in a stable state and do not need to gain or lose electrons to achieve stability.

How many electrons does an argon atom have, and what is its electron arrangement?

An argon atom has 18 electrons due to its atomic number. Its electron arrangement is 2 electrons in the first shell, 8 in the second, and 8 in the third shell, which can be represented as 2, 8, 8.

What is the electron arrangement for calcium, and why is it not stable?

Calcium has an atomic number of 20, so it has 20 electrons arranged as 2 in the first shell, 8 in the second, 8 in the third, and 2 in the fourth shell. It is not stable because its outermost shell does not have a full complement of 8 electrons.

What happens when a calcium atom loses its two outermost electrons?

When a calcium atom loses its two outermost electrons, it forms a calcium ion with a 2+ positive charge. The outermost shell then becomes the third shell, which is now full, making the ion stable.

What is the atomic number of fluorine, and what is its electron arrangement?

Fluorine has an atomic number of 9, indicating it has 9 electrons. Its electron arrangement is 2 electrons in the first shell and 7 in the second shell, represented as 2, 7.

Why does a fluorine atom need to gain an electron to be stable?

A fluorine atom needs to gain an electron to be stable because it has 7 electrons in its second shell, which is one electron short of the stable configuration of 8 electrons in the outer shell.

What is the resulting charge of a fluorine atom after it gains an electron?

After gaining an electron, a fluorine atom becomes a fluoride ion with an overall charge of -1.

Outlines

00:00

🔬 Electron Arrangement and Atomic Stability

This paragraph delves into the electron configuration in atoms, emphasizing the importance of a full outer electron shell for atomic stability. It uses the example of a fluorine atom to illustrate the concept of incomplete outer shells and the subsequent need for atoms to react with others to achieve stability. The paragraph introduces the electron arrangement of sodium, explaining its atomic number and the shell structure, including the specific electron placement within each shell. It highlights the instability of sodium due to its incomplete outer shell and contrasts this with noble gases, which have full outer shells and are chemically inert. The video script also covers how to determine the electron structure of argon and calcium, explaining the process of drawing electron shells and the significance of a full outer shell for stability, leading to the formation of ions when atoms lose or gain electrons to achieve this state.

05:01

🚀 Understanding Ions and Electron Configurations

The second paragraph continues the discussion on atomic stability by focusing on ions, specifically using calcium and fluorine as examples. It explains how calcium, with 20 electrons, forms a calcium ion by losing two electrons to achieve a stable electron configuration, resulting in a positively charged ion. The paragraph details the notation for ions, including the use of square brackets and the indication of the overall charge. It also contrasts this with fluorine, which gains an electron to complete its outer shell, becoming a negatively charged fluoride ion. The summary concludes with the electron configurations for both calcium and fluorine in their ionic forms, highlighting the changes in electron count and charge that result from the atoms' pursuit of a stable electron configuration.

Keywords

💡Electron arrangement

Electron arrangement refers to the distribution of electrons in an atom's electron shells. This concept is central to the video's theme as it explains how atoms strive for stability by having a full outer shell. For example, the script discusses the electron arrangement of sodium, which has 11 electrons distributed across three shells, indicating its instability due to the incomplete outer shell.

💡Atomic number

The atomic number is the number of protons in an atom's nucleus, which is also equal to the number of electrons in a neutral atom. It is fundamental to understanding electron arrangements, as demonstrated in the video when determining the electron configuration of sodium with an atomic number of 11.

💡Electron shell

An electron shell is a region around the nucleus where electrons are located. The video script explains that electrons are arranged in shells, with the first shell holding up to two electrons and the second and third shells holding up to eight each, which is crucial for understanding atomic stability.

💡Stability

In the context of the video, stability refers to an atom having a full outer electron shell, which is typically eight electrons for most elements. The script uses the example of sodium, which has only one electron in its outer shell, to illustrate the concept of instability and the atom's tendency to react to achieve a stable configuration.

💡Noble gases

Noble gases, found in Group 0 of the periodic table, are highlighted in the video as exceptions to the rule of seeking stability. They have full outer electron shells, such as neon, and are chemically inert because they do not need to gain or lose electrons to achieve stability.

💡Electron configuration

Electron configuration is the description of the distribution of an atom's electrons among its electron shells. The video script provides examples of how to determine the electron configuration for elements like argon and calcium, which is essential for understanding their chemical properties and reactivity.

💡Ion

An ion is an atom or molecule that has an unequal number of protons and electrons, resulting in a net electrical charge. The video explains how atoms like calcium can become ions by losing electrons to achieve a stable electron configuration, as seen in the formation of a calcium ion with a 2+ charge.

💡Charge

The charge of an ion is the result of the imbalance between the number of protons and electrons. The video script discusses how atoms like calcium can have a positive charge after losing electrons, and fluorine can have a negative charge after gaining an electron, leading to the formation of ions.

💡Periodic table

The periodic table is a tabular arrangement of the chemical elements, ordered by their atomic number, electron configuration, and recurring chemical properties. The video script uses the periodic table to identify elements like argon and their atomic numbers, which is essential for determining their electron configurations.

💡Chemical reaction

A chemical reaction involves the rearrangement of electrons and the formation or breaking of chemical bonds between atoms. The video script implies that atoms with incomplete outer shells, such as sodium and fluorine, will undergo chemical reactions to achieve stability by gaining or losing electrons.

💡Electron capacity

Electron capacity refers to the maximum number of electrons a shell can hold. The video script explains that the first shell can hold up to two electrons, while the second and third shells can hold up to eight, which is a key factor in determining an atom's stability and reactivity.

Highlights

Video explores electron arrangement in atoms and its importance for atomic stability.

Atoms with incomplete outer shells, like fluorine, tend to react to achieve stability.

Sodium's electron arrangement is demonstrated with its atomic number of 11.

Electron shells fill in a specific order, starting with the lowest energy level closest to the nucleus.

The first electron shell can hold a maximum of two electrons.

The second shell can hold up to eight electrons, following a specific arrangement pattern.

Sodium's outer shell has only one electron, indicating instability and the need to react.

Atoms generally want to form molecules or compounds to achieve a full outer shell.

Noble gases, like neon, have full outer shells and are chemically stable due to this.

Argon's electron structure is explained with its atomic number of 18.

Electron arrangements can be represented numerically, as shown with argon's 2,8,8 structure.

Calcium, with an atomic number of 20, has an unstable electron arrangement.

Calcium atoms can become stable by losing two electrons, forming a calcium ion.

Ions are represented with square brackets and the overall charge indicated.

Fluorine, with an atomic number of 9, needs to gain an electron to achieve a full outer shell.

Fluorine forms a fluoride ion with a charge of minus one when it gains an electron.

The video concludes with a teaser for the next topic: balancing chemical equations.

Transcripts

in today's video we're going to take a

look at the arrangement of electrons in

atoms

and see how most atoms like the fluorine

that we've shown here have an incomplete

outer shell of electrons

this is a really key point in chemistry

because in order for atoms to be stable

they need to have a full outer shell

and if they don't then they'll have to

react with another atom they gain or

lose the electrons that they need

let's start by drawing the electron

arrangement of sodium

the fact that it has an atomic number of

11 tells us that there's 11 protons

but also that it has 11 electrons

these electrons are going to be arranged

in shells around the nucleus

which we draw as rings like this

and the first one to fill is the one

closest to the nucleus

as this one will have the lowest energy

level

this first shell can only hold two

electrons

the second shell though can hold up to

eight

and the order in which you add them can

sometimes be important

the best way to do it is to put a single

electron in the top

right bottom and left positions

before you go around again to put a

second electron in each position

this might seem a bit weird or

unnecessary but really you're just

adding them in clockwise until you've

either filled the shell or run out of

electrons

as we still have one electron left we

put it in the third shell

and just like the second shell the third

one can hold a maximum of eight

electrons

in order for atoms to be stable their

outermost shell meaning the one furthest

from the nucleus needs to be completely

full

you can see here that our sodium atom

only has one electron in its outer shell

rather than eight

so we would say that it's unstable

and all we mean by that is that it wants

to react with another atom so that it

can have a full outer shell

now most single atoms are like the

sodium that we just saw

if they weren't bonded to anything then

they would have incomplete outer shells

and so to fix this most atoms want to

react to form molecules or compounds

however there are some exceptions to

this

the noble gases in group zero of the

periodic table

all have completely full outer shells

as we can see with neon

and because of this they don't want to

lose or gain any electrons

and so they don't really react with

anything

when it comes to exams you could be

asked to work out the electron

arrangement of any of the first 20

elements in the periodic table

for example they could ask

what is the electron structure of argon

for this we first need to find argon on

the periodic table

and we can see that argon has an atomic

number of 18.

so we must also have 18 electrons

then after drawing a quick nucleus we

can start to draw the shells and

electrons

the first shell will have two electrons

the second shell will have eight and the

third shell will also have eight

because two plus eight plus eight gives

us eighteen

we can also show this electron structure

with numbers though rather than drawing

out all of these shells

and to do that we would just do two

comma eight comma eight

to show there's two electrons in the

first shell

eight in the second and eight in the

third

another thing to point out is that when

you come to draw these diagrams for

yourself you have to draw the electrons

either as crosses like this

or as dots like this one

what if we were asked to do the same for

calcium

well calcium has an atomic number of 20

so it must have 20 electrons

which means working out from our nucleus

we have two in the first shell

eight in the second

eight in the third

and two in the fourth

and if we were to write this structure

it would just be two

eight eight two

as we can see from this diagram calcium

atoms aren't stable

because they don't have a full outer

shell

they only have two out of eight possible

electrons in their fourth shell

what would help is if these two outer

electrons were somehow removed

this would mean that the outermost shell

which is now the third shell

would be full and so the calcium is

stable

however even though our calcium atom

still has 20 positive protons

it now has only 18 negative electrons

because remember it just lost two of

them

so overall it's gonna have a two plus

positive charge

and so we call it a calcium ion rather

than a calcium atom

with ions we always draw big square

brackets around them

and write the overall charge in the top

right corner

because our calcium atom lost two

electrons drew right to the electron

structure it would now just be two eight

eight

as a last example let's look at fluorine

its atomic number is nine so there are

nine protons and nine electrons

meaning we'd have two electrons in the

first shell and seven in the second

which we'd write as two comma seven

so here we'd have the opposite problem

to what we had with calcium

in order to be stable and have a full

outer shell fluorine needs to gain one

more electron

which you would have to get from another

atom

giving it an overall charge of minus one

and making it a one minus fluoride ion

and we could write this electron

structure as 2 8.

anyway that's it for this video if you

enjoyed it then please do give us a like

and we'll see you next time when we take

a look at how to balance chemical

equations